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Count Tokens

post /v1/messages/count_tokens

Count the number of tokens in a Message.

The Token Count API can be used to count the number of tokens in a Message, including tools, images, and documents, without creating it.

Learn more about token counting in our user guide

Body Parameters

  • messages: array of MessageParam

    Input messages.

    Our models are trained to operate on alternating user and assistant conversational turns. When creating a new Message, you specify the prior conversational turns with the messages parameter, and the model then generates the next Message in the conversation. Consecutive user or assistant turns in your request will be combined into a single turn.

    Each input message must be an object with a role and content. You can specify a single user-role message, or you can include multiple user and assistant messages.

    If the final message uses the assistant role, the response content will continue immediately from the content in that message. This can be used to constrain part of the model's response.

    Example with a single user message:

    [{"role": "user", "content": "Hello, Claude"}]

    Example with multiple conversational turns:

    [
  {"role": "user", "content": "Hello there."},
  {"role": "assistant", "content": "Hi, I'm Claude. How can I help you?"},
  {"role": "user", "content": "Can you explain LLMs in plain English?"},
]

    Example with a partially-filled response from Claude:

    [
  {"role": "user", "content": "What's the Greek name for Sun? (A) Sol (B) Helios (C) Sun"},
  {"role": "assistant", "content": "The best answer is ("},
]

    Each input message content may be either a single string or an array of content blocks, where each block has a specific type. Using a string for content is shorthand for an array of one content block of type "text". The following input messages are equivalent:

    {"role": "user", "content": "Hello, Claude"}

    {"role": "user", "content": [{"type": "text", "text": "Hello, Claude"}]}

    See input examples.

    Note that if you want to include a system prompt, you can use the top-level system parameter — there is no "system" role for input messages in the Messages API.

    There is a limit of 100,000 messages in a single request.

    • content: string or array of ContentBlockParam

      • UnionMember0 = string

      • UnionMember1 = array of ContentBlockParam

        • TextBlockParam = object { text, type, cache_control, citations }

          • text: string

          • type: "text"

            • "text"

          • cache_control: optional CacheControlEphemeral

            Create a cache control breakpoint at this content block.

            • type: "ephemeral"

              • "ephemeral"

            • ttl: optional "5m" or "1h"

              The time-to-live for the cache control breakpoint.

              This may be one the following values:

              • 5m: 5 minutes
              • 1h: 1 hour

              Defaults to 5m.

              • "5m"

              • "1h"

          • citations: optional array of TextCitationParam

            • CitationCharLocationParam = object { cited_text, document_index, document_title, 3 more }

              • cited_text: string

              • document_index: number

              • document_title: string

              • end_char_index: number

              • start_char_index: number

              • type: "char_location"

                • "char_location"

            • CitationPageLocationParam = object { cited_text, document_index, document_title, 3 more }

              • cited_text: string

              • document_index: number

              • document_title: string

              • end_page_number: number

              • start_page_number: number

              • type: "page_location"

                • "page_location"

            • CitationContentBlockLocationParam = object { cited_text, document_index, document_title, 3 more }

              • cited_text: string

              • document_index: number

              • document_title: string

              • end_block_index: number

              • start_block_index: number

              • type: "content_block_location"

                • "content_block_location"

            • CitationWebSearchResultLocationParam = object { cited_text, encrypted_index, title, 2 more }

              • cited_text: string

              • encrypted_index: string

              • title: string

              • type: "web_search_result_location"

                • "web_search_result_location"

              • url: string

            • CitationSearchResultLocationParam = object { cited_text, end_block_index, search_result_index, 4 more }

              • cited_text: string

              • end_block_index: number

              • search_result_index: number

              • source: string

              • start_block_index: number

              • title: string

              • type: "search_result_location"

                • "search_result_location"

        • ImageBlockParam = object { source, type, cache_control }

          • source: Base64ImageSource or URLImageSource

            • Base64ImageSource = object { data, media_type, type }

              • data: string

              • media_type: "image/jpeg" or "image/png" or "image/gif" or "image/webp"

                • "image/jpeg"

                • "image/png"

                • "image/gif"

                • "image/webp"

              • type: "base64"

                • "base64"

            • URLImageSource = object { type, url }

              • type: "url"

                • "url"

              • url: string

          • type: "image"

            • "image"

          • cache_control: optional CacheControlEphemeral

            Create a cache control breakpoint at this content block.

            • type: "ephemeral"

              • "ephemeral"

            • ttl: optional "5m" or "1h"

              The time-to-live for the cache control breakpoint.

              This may be one the following values:

              • 5m: 5 minutes
              • 1h: 1 hour

              Defaults to 5m.

              • "5m"

              • "1h"

        • DocumentBlockParam = object { source, type, cache_control, 3 more }

          • source: Base64PDFSource or PlainTextSource or ContentBlockSource or URLPDFSource

            • Base64PDFSource = object { data, media_type, type }

              • data: string

              • media_type: "application/pdf"

                • "application/pdf"

              • type: "base64"

                • "base64"

            • PlainTextSource = object { data, media_type, type }

              • data: string

              • media_type: "text/plain"

                • "text/plain"

              • type: "text"

                • "text"

            • ContentBlockSource = object { content, type }

              • content: string or array of ContentBlockSourceContent

                • UnionMember0 = string

                • ContentBlockSourceContent = array of ContentBlockSourceContent

                  • TextBlockParam = object { text, type, cache_control, citations }

                    • text: string

                    • type: "text"

                      • "text"

                    • cache_control: optional CacheControlEphemeral

                      Create a cache control breakpoint at this content block.

                      • type: "ephemeral"

                        • "ephemeral"

                      • ttl: optional "5m" or "1h"

                        The time-to-live for the cache control breakpoint.

                        This may be one the following values:

                        • 5m: 5 minutes
                        • 1h: 1 hour

                        Defaults to 5m.

                        • "5m"

                        • "1h"

                    • citations: optional array of TextCitationParam

                      • CitationCharLocationParam = object { cited_text, document_index, document_title, 3 more }

                        • cited_text: string

                        • document_index: number

                        • document_title: string

                        • end_char_index: number

                        • start_char_index: number

                        • type: "char_location"

                          • "char_location"

                      • CitationPageLocationParam = object { cited_text, document_index, document_title, 3 more }

                        • cited_text: string

                        • document_index: number

                        • document_title: string

                        • end_page_number: number

                        • start_page_number: number

                        • type: "page_location"

                          • "page_location"

                      • CitationContentBlockLocationParam = object { cited_text, document_index, document_title, 3 more }

                        • cited_text: string

                        • document_index: number

                        • document_title: string

                        • end_block_index: number

                        • start_block_index: number

                        • type: "content_block_location"

                          • "content_block_location"

                      • CitationWebSearchResultLocationParam = object { cited_text, encrypted_index, title, 2 more }

                        • cited_text: string

                        • encrypted_index: string

                        • title: string

                        • type: "web_search_result_location"

                          • "web_search_result_location"

                        • url: string

                      • CitationSearchResultLocationParam = object { cited_text, end_block_index, search_result_index, 4 more }

                        • cited_text: string

                        • end_block_index: number

                        • search_result_index: number

                        • source: string

                        • start_block_index: number

                        • title: string

                        • type: "search_result_location"

                          • "search_result_location"

                  • ImageBlockParam = object { source, type, cache_control }

                    • source: Base64ImageSource or URLImageSource

                      • Base64ImageSource = object { data, media_type, type }

                        • data: string

                        • media_type: "image/jpeg" or "image/png" or "image/gif" or "image/webp"

                          • "image/jpeg"

                          • "image/png"

                          • "image/gif"

                          • "image/webp"

                        • type: "base64"

                          • "base64"

                      • URLImageSource = object { type, url }

                        • type: "url"

                          • "url"

                        • url: string

                    • type: "image"

                      • "image"

                    • cache_control: optional CacheControlEphemeral

                      Create a cache control breakpoint at this content block.

                      • type: "ephemeral"

                        • "ephemeral"

                      • ttl: optional "5m" or "1h"

                        The time-to-live for the cache control breakpoint.

                        This may be one the following values:

                        • 5m: 5 minutes
                        • 1h: 1 hour

                        Defaults to 5m.

                        • "5m"

                        • "1h"

              • type: "content"

                • "content"

            • URLPDFSource = object { type, url }

              • type: "url"

                • "url"

              • url: string

          • type: "document"

            • "document"

          • cache_control: optional CacheControlEphemeral

            Create a cache control breakpoint at this content block.

            • type: "ephemeral"

              • "ephemeral"

            • ttl: optional "5m" or "1h"

              The time-to-live for the cache control breakpoint.

              This may be one the following values:

              • 5m: 5 minutes
              • 1h: 1 hour

              Defaults to 5m.

              • "5m"

              • "1h"

          • citations: optional CitationsConfigParam

            • enabled: optional boolean

          • context: optional string

          • title: optional string

        • SearchResultBlockParam = object { content, source, title, 3 more }

          • content: array of TextBlockParam

            • text: string

            • type: "text"

              • "text"

            • cache_control: optional CacheControlEphemeral

              Create a cache control breakpoint at this content block.

              • type: "ephemeral"

                • "ephemeral"

              • ttl: optional "5m" or "1h"

                The time-to-live for the cache control breakpoint.

                This may be one the following values:

                • 5m: 5 minutes
                • 1h: 1 hour

                Defaults to 5m.

                • "5m"

                • "1h"

            • citations: optional array of TextCitationParam

              • CitationCharLocationParam = object { cited_text, document_index, document_title, 3 more }

                • cited_text: string

                • document_index: number

                • document_title: string

                • end_char_index: number

                • start_char_index: number

                • type: "char_location"

                  • "char_location"

              • CitationPageLocationParam = object { cited_text, document_index, document_title, 3 more }

                • cited_text: string

                • document_index: number

                • document_title: string

                • end_page_number: number

                • start_page_number: number

                • type: "page_location"

                  • "page_location"

              • CitationContentBlockLocationParam = object { cited_text, document_index, document_title, 3 more }

                • cited_text: string

                • document_index: number

                • document_title: string

                • end_block_index: number

                • start_block_index: number

                • type: "content_block_location"

                  • "content_block_location"

              • CitationWebSearchResultLocationParam = object { cited_text, encrypted_index, title, 2 more }

                • cited_text: string

                • encrypted_index: string

                • title: string

                • type: "web_search_result_location"

                  • "web_search_result_location"

                • url: string

              • CitationSearchResultLocationParam = object { cited_text, end_block_index, search_result_index, 4 more }

                • cited_text: string

                • end_block_index: number

                • search_result_index: number

                • source: string

                • start_block_index: number

                • title: string

                • type: "search_result_location"

                  • "search_result_location"

          • source: string

          • title: string

          • type: "search_result"

            • "search_result"

          • cache_control: optional CacheControlEphemeral

            Create a cache control breakpoint at this content block.

            • type: "ephemeral"

              • "ephemeral"

            • ttl: optional "5m" or "1h"

              The time-to-live for the cache control breakpoint.

              This may be one the following values:

              • 5m: 5 minutes
              • 1h: 1 hour

              Defaults to 5m.

              • "5m"

              • "1h"

          • citations: optional CitationsConfigParam

            • enabled: optional boolean

        • ThinkingBlockParam = object { signature, thinking, type }

          • signature: string

          • thinking: string

          • type: "thinking"

            • "thinking"

        • RedactedThinkingBlockParam = object { data, type }

          • data: string

          • type: "redacted_thinking"

            • "redacted_thinking"

        • ToolUseBlockParam = object { id, input, name, 3 more }

          • id: string

          • input: map[unknown]

          • name: string

          • type: "tool_use"

            • "tool_use"

          • cache_control: optional CacheControlEphemeral

            Create a cache control breakpoint at this content block.

            • type: "ephemeral"

              • "ephemeral"

            • ttl: optional "5m" or "1h"

              The time-to-live for the cache control breakpoint.

              This may be one the following values:

              • 5m: 5 minutes
              • 1h: 1 hour

              Defaults to 5m.

              • "5m"

              • "1h"

          • caller: optional DirectCaller or ServerToolCaller or ServerToolCaller20260120

            Tool invocation directly from the model.

            • DirectCaller = object { type }

              Tool invocation directly from the model.

              • type: "direct"

                • "direct"

            • ServerToolCaller = object { tool_id, type }

              Tool invocation generated by a server-side tool.

              • tool_id: string

              • type: "code_execution_20250825"

                • "code_execution_20250825"

            • ServerToolCaller20260120 = object { tool_id, type }

              • tool_id: string

              • type: "code_execution_20260120"

                • "code_execution_20260120"

        • ToolResultBlockParam = object { tool_use_id, type, cache_control, 2 more }

          • tool_use_id: string

          • type: "tool_result"

            • "tool_result"

          • cache_control: optional CacheControlEphemeral

            Create a cache control breakpoint at this content block.

            • type: "ephemeral"

              • "ephemeral"

            • ttl: optional "5m" or "1h"

              The time-to-live for the cache control breakpoint.

              This may be one the following values:

              • 5m: 5 minutes
              • 1h: 1 hour

              Defaults to 5m.

              • "5m"

              • "1h"

          • content: optional string or array of TextBlockParam or ImageBlockParam or SearchResultBlockParam or 2 more

            • UnionMember0 = string

            • UnionMember1 = array of TextBlockParam or ImageBlockParam or SearchResultBlockParam or 2 more

              • TextBlockParam = object { text, type, cache_control, citations }

                • text: string

                • type: "text"

                  • "text"

                • cache_control: optional CacheControlEphemeral

                  Create a cache control breakpoint at this content block.

                  • type: "ephemeral"

                    • "ephemeral"

                  • ttl: optional "5m" or "1h"

                    The time-to-live for the cache control breakpoint.

                    This may be one the following values:

                    • 5m: 5 minutes
                    • 1h: 1 hour

                    Defaults to 5m.

                    • "5m"

                    • "1h"

                • citations: optional array of TextCitationParam

                  • CitationCharLocationParam = object { cited_text, document_index, document_title, 3 more }

                    • cited_text: string

                    • document_index: number

                    • document_title: string

                    • end_char_index: number

                    • start_char_index: number

                    • type: "char_location"

                      • "char_location"

                  • CitationPageLocationParam = object { cited_text, document_index, document_title, 3 more }

                    • cited_text: string

                    • document_index: number

                    • document_title: string

                    • end_page_number: number

                    • start_page_number: number

                    • type: "page_location"

                      • "page_location"

                  • CitationContentBlockLocationParam = object { cited_text, document_index, document_title, 3 more }

                    • cited_text: string

                    • document_index: number

                    • document_title: string

                    • end_block_index: number

                    • start_block_index: number

                    • type: "content_block_location"

                      • "content_block_location"

                  • CitationWebSearchResultLocationParam = object { cited_text, encrypted_index, title, 2 more }

                    • cited_text: string

                    • encrypted_index: string

                    • title: string

                    • type: "web_search_result_location"

                      • "web_search_result_location"

                    • url: string

                  • CitationSearchResultLocationParam = object { cited_text, end_block_index, search_result_index, 4 more }

                    • cited_text: string

                    • end_block_index: number

                    • search_result_index: number

                    • source: string

                    • start_block_index: number

                    • title: string

                    • type: "search_result_location"

                      • "search_result_location"

              • ImageBlockParam = object { source, type, cache_control }

                • source: Base64ImageSource or URLImageSource

                  • Base64ImageSource = object { data, media_type, type }

                    • data: string

                    • media_type: "image/jpeg" or "image/png" or "image/gif" or "image/webp"

                      • "image/jpeg"

                      • "image/png"

                      • "image/gif"

                      • "image/webp"

                    • type: "base64"

                      • "base64"

                  • URLImageSource = object { type, url }

                    • type: "url"

                      • "url"

                    • url: string

                • type: "image"

                  • "image"

                • cache_control: optional CacheControlEphemeral

                  Create a cache control breakpoint at this content block.

                  • type: "ephemeral"

                    • "ephemeral"

                  • ttl: optional "5m" or "1h"

                    The time-to-live for the cache control breakpoint.

                    This may be one the following values:

                    • 5m: 5 minutes
                    • 1h: 1 hour

                    Defaults to 5m.

                    • "5m"

                    • "1h"

              • SearchResultBlockParam = object { content, source, title, 3 more }

                • content: array of TextBlockParam

                  • text: string

                  • type: "text"

                    • "text"

                  • cache_control: optional CacheControlEphemeral

                    Create a cache control breakpoint at this content block.

                    • type: "ephemeral"

                      • "ephemeral"

                    • ttl: optional "5m" or "1h"

                      The time-to-live for the cache control breakpoint.

                      This may be one the following values:

                      • 5m: 5 minutes
                      • 1h: 1 hour

                      Defaults to 5m.

                      • "5m"

                      • "1h"

                  • citations: optional array of TextCitationParam

                    • CitationCharLocationParam = object { cited_text, document_index, document_title, 3 more }

                      • cited_text: string

                      • document_index: number

                      • document_title: string

                      • end_char_index: number

                      • start_char_index: number

                      • type: "char_location"

                        • "char_location"

                    • CitationPageLocationParam = object { cited_text, document_index, document_title, 3 more }

                      • cited_text: string

                      • document_index: number

                      • document_title: string

                      • end_page_number: number

                      • start_page_number: number

                      • type: "page_location"

                        • "page_location"

                    • CitationContentBlockLocationParam = object { cited_text, document_index, document_title, 3 more }

                      • cited_text: string

                      • document_index: number

                      • document_title: string

                      • end_block_index: number

                      • start_block_index: number

                      • type: "content_block_location"

                        • "content_block_location"

                    • CitationWebSearchResultLocationParam = object { cited_text, encrypted_index, title, 2 more }

                      • cited_text: string

                      • encrypted_index: string

                      • title: string

                      • type: "web_search_result_location"

                        • "web_search_result_location"

                      • url: string

                    • CitationSearchResultLocationParam = object { cited_text, end_block_index, search_result_index, 4 more }

                      • cited_text: string

                      • end_block_index: number

                      • search_result_index: number

                      • source: string

                      • start_block_index: number

                      • title: string

                      • type: "search_result_location"

                        • "search_result_location"

                • source: string

                • title: string

                • type: "search_result"

                  • "search_result"

                • cache_control: optional CacheControlEphemeral

                  Create a cache control breakpoint at this content block.

                  • type: "ephemeral"

                    • "ephemeral"

                  • ttl: optional "5m" or "1h"

                    The time-to-live for the cache control breakpoint.

                    This may be one the following values:

                    • 5m: 5 minutes
                    • 1h: 1 hour

                    Defaults to 5m.

                    • "5m"

                    • "1h"

                • citations: optional CitationsConfigParam

                  • enabled: optional boolean

              • DocumentBlockParam = object { source, type, cache_control, 3 more }

                • source: Base64PDFSource or PlainTextSource or ContentBlockSource or URLPDFSource

                  • Base64PDFSource = object { data, media_type, type }

                    • data: string

                    • media_type: "application/pdf"

                      • "application/pdf"

                    • type: "base64"

                      • "base64"

                  • PlainTextSource = object { data, media_type, type }

                    • data: string

                    • media_type: "text/plain"

                      • "text/plain"

                    • type: "text"

                      • "text"

                  • ContentBlockSource = object { content, type }

                    • content: string or array of ContentBlockSourceContent

                      • UnionMember0 = string

                      • ContentBlockSourceContent = array of ContentBlockSourceContent

                        • TextBlockParam = object { text, type, cache_control, citations }

                          • text: string

                          • type: "text"

                            • "text"

                          • cache_control: optional CacheControlEphemeral

                            Create a cache control breakpoint at this content block.

                            • type: "ephemeral"

                              • "ephemeral"

                            • ttl: optional "5m" or "1h"

                              The time-to-live for the cache control breakpoint.

                              This may be one the following values:

                              • 5m: 5 minutes
                              • 1h: 1 hour

                              Defaults to 5m.

                              • "5m"

                              • "1h"

                          • citations: optional array of TextCitationParam

                            • CitationCharLocationParam = object { cited_text, document_index, document_title, 3 more }

                              • cited_text: string

                              • document_index: number

                              • document_title: string

                              • end_char_index: number

                              • start_char_index: number

                              • type: "char_location"

                                • "char_location"

                            • CitationPageLocationParam = object { cited_text, document_index, document_title, 3 more }

                              • cited_text: string

                              • document_index: number

                              • document_title: string

                              • end_page_number: number

                              • start_page_number: number

                              • type: "page_location"

                                • "page_location"

                            • CitationContentBlockLocationParam = object { cited_text, document_index, document_title, 3 more }

                              • cited_text: string

                              • document_index: number

                              • document_title: string

                              • end_block_index: number

                              • start_block_index: number

                              • type: "content_block_location"

                                • "content_block_location"

                            • CitationWebSearchResultLocationParam = object { cited_text, encrypted_index, title, 2 more }

                              • cited_text: string

                              • encrypted_index: string

                              • title: string

                              • type: "web_search_result_location"

                                • "web_search_result_location"

                              • url: string

                            • CitationSearchResultLocationParam = object { cited_text, end_block_index, search_result_index, 4 more }

                              • cited_text: string

                              • end_block_index: number

                              • search_result_index: number

                              • source: string

                              • start_block_index: number

                              • title: string

                              • type: "search_result_location"

                                • "search_result_location"

                        • ImageBlockParam = object { source, type, cache_control }

                          • source: Base64ImageSource or URLImageSource

                            • Base64ImageSource = object { data, media_type, type }

                              • data: string

                              • media_type: "image/jpeg" or "image/png" or "image/gif" or "image/webp"

                                • "image/jpeg"

                                • "image/png"

                                • "image/gif"

                                • "image/webp"

                              • type: "base64"

                                • "base64"

                            • URLImageSource = object { type, url }

                              • type: "url"

                                • "url"

                              • url: string

                          • type: "image"

                            • "image"

                          • cache_control: optional CacheControlEphemeral

                            Create a cache control breakpoint at this content block.

                            • type: "ephemeral"

                              • "ephemeral"

                            • ttl: optional "5m" or "1h"

                              The time-to-live for the cache control breakpoint.

                              This may be one the following values:

                              • 5m: 5 minutes
                              • 1h: 1 hour

                              Defaults to 5m.

                              • "5m"

                              • "1h"

                    • type: "content"

                      • "content"

                  • URLPDFSource = object { type, url }

                    • type: "url"

                      • "url"

                    • url: string

                • type: "document"

                  • "document"

                • cache_control: optional CacheControlEphemeral

                  Create a cache control breakpoint at this content block.

                  • type: "ephemeral"

                    • "ephemeral"

                  • ttl: optional "5m" or "1h"

                    The time-to-live for the cache control breakpoint.

                    This may be one the following values:

                    • 5m: 5 minutes
                    • 1h: 1 hour

                    Defaults to 5m.

                    • "5m"

                    • "1h"

                • citations: optional CitationsConfigParam

                  • enabled: optional boolean

                • context: optional string

                • title: optional string

              • ToolReferenceBlockParam = object { tool_name, type, cache_control }

                Tool reference block that can be included in tool_result content.

                • tool_name: string

                • type: "tool_reference"

                  • "tool_reference"

                • cache_control: optional CacheControlEphemeral

                  Create a cache control breakpoint at this content block.

                  • type: "ephemeral"

                    • "ephemeral"

                  • ttl: optional "5m" or "1h"

                    The time-to-live for the cache control breakpoint.

                    This may be one the following values:

                    • 5m: 5 minutes
                    • 1h: 1 hour

                    Defaults to 5m.

                    • "5m"

                    • "1h"

          • is_error: optional boolean

        • ServerToolUseBlockParam = object { id, input, name, 3 more }

          • id: string

          • input: map[unknown]

          • name: "web_search" or "web_fetch" or "code_execution" or 4 more

            • "web_search"

            • "web_fetch"

            • "code_execution"

            • "bash_code_execution"

            • "text_editor_code_execution"

            • "tool_search_tool_regex"

            • "tool_search_tool_bm25"

          • type: "server_tool_use"

            • "server_tool_use"

          • cache_control: optional CacheControlEphemeral

            Create a cache control breakpoint at this content block.

            • type: "ephemeral"

              • "ephemeral"

            • ttl: optional "5m" or "1h"

              The time-to-live for the cache control breakpoint.

              This may be one the following values:

              • 5m: 5 minutes
              • 1h: 1 hour

              Defaults to 5m.

              • "5m"

              • "1h"

          • caller: optional DirectCaller or ServerToolCaller or ServerToolCaller20260120

            Tool invocation directly from the model.

            • DirectCaller = object { type }

              Tool invocation directly from the model.

              • type: "direct"

                • "direct"

            • ServerToolCaller = object { tool_id, type }

              Tool invocation generated by a server-side tool.

              • tool_id: string

              • type: "code_execution_20250825"

                • "code_execution_20250825"

            • ServerToolCaller20260120 = object { tool_id, type }

              • tool_id: string

              • type: "code_execution_20260120"

                • "code_execution_20260120"

        • WebSearchToolResultBlockParam = object { content, tool_use_id, type, 2 more }

          • content: WebSearchToolResultBlockParamContent

            • WebSearchToolResultBlockItem = array of WebSearchResultBlockParam

              • encrypted_content: string

              • title: string

              • type: "web_search_result"

                • "web_search_result"

              • url: string

              • page_age: optional string

            • WebSearchToolRequestError = object { error_code, type }

              • error_code: WebSearchToolResultErrorCode

                • "invalid_tool_input"

                • "unavailable"

                • "max_uses_exceeded"

                • "too_many_requests"

                • "query_too_long"

                • "request_too_large"

              • type: "web_search_tool_result_error"

                • "web_search_tool_result_error"

          • tool_use_id: string

          • type: "web_search_tool_result"

            • "web_search_tool_result"

          • cache_control: optional CacheControlEphemeral

            Create a cache control breakpoint at this content block.

            • type: "ephemeral"

              • "ephemeral"

            • ttl: optional "5m" or "1h"

              The time-to-live for the cache control breakpoint.

              This may be one the following values:

              • 5m: 5 minutes
              • 1h: 1 hour

              Defaults to 5m.

              • "5m"

              • "1h"

          • caller: optional DirectCaller or ServerToolCaller or ServerToolCaller20260120

            Tool invocation directly from the model.

            • DirectCaller = object { type }

              Tool invocation directly from the model.

              • type: "direct"

                • "direct"

            • ServerToolCaller = object { tool_id, type }

              Tool invocation generated by a server-side tool.

              • tool_id: string

              • type: "code_execution_20250825"

                • "code_execution_20250825"

            • ServerToolCaller20260120 = object { tool_id, type }

              • tool_id: string

              • type: "code_execution_20260120"

                • "code_execution_20260120"

        • WebFetchToolResultBlockParam = object { content, tool_use_id, type, 2 more }

          • content: WebFetchToolResultErrorBlockParam or WebFetchBlockParam

            • WebFetchToolResultErrorBlockParam = object { error_code, type }

              • error_code: WebFetchToolResultErrorCode

                • "invalid_tool_input"

                • "url_too_long"

                • "url_not_allowed"

                • "url_not_accessible"

                • "unsupported_content_type"

                • "too_many_requests"

                • "max_uses_exceeded"

                • "unavailable"

              • type: "web_fetch_tool_result_error"

                • "web_fetch_tool_result_error"

            • WebFetchBlockParam = object { content, type, url, retrieved_at }

              • content: DocumentBlockParam

                • source: Base64PDFSource or PlainTextSource or ContentBlockSource or URLPDFSource

                  • Base64PDFSource = object { data, media_type, type }

                    • data: string

                    • media_type: "application/pdf"

                      • "application/pdf"

                    • type: "base64"

                      • "base64"

                  • PlainTextSource = object { data, media_type, type }

                    • data: string

                    • media_type: "text/plain"

                      • "text/plain"

                    • type: "text"

                      • "text"

                  • ContentBlockSource = object { content, type }

                    • content: string or array of ContentBlockSourceContent

                      • UnionMember0 = string

                      • ContentBlockSourceContent = array of ContentBlockSourceContent

                        • TextBlockParam = object { text, type, cache_control, citations }

                          • text: string

                          • type: "text"

                            • "text"

                          • cache_control: optional CacheControlEphemeral

                            Create a cache control breakpoint at this content block.

                            • type: "ephemeral"

                              • "ephemeral"

                            • ttl: optional "5m" or "1h"

                              The time-to-live for the cache control breakpoint.

                              This may be one the following values:

                              • 5m: 5 minutes
                              • 1h: 1 hour

                              Defaults to 5m.

                              • "5m"

                              • "1h"

                          • citations: optional array of TextCitationParam

                            • CitationCharLocationParam = object { cited_text, document_index, document_title, 3 more }

                              • cited_text: string

                              • document_index: number

                              • document_title: string

                              • end_char_index: number

                              • start_char_index: number

                              • type: "char_location"

                                • "char_location"

                            • CitationPageLocationParam = object { cited_text, document_index, document_title, 3 more }

                              • cited_text: string

                              • document_index: number

                              • document_title: string

                              • end_page_number: number

                              • start_page_number: number

                              • type: "page_location"

                                • "page_location"

                            • CitationContentBlockLocationParam = object { cited_text, document_index, document_title, 3 more }

                              • cited_text: string

                              • document_index: number

                              • document_title: string

                              • end_block_index: number

                              • start_block_index: number

                              • type: "content_block_location"

                                • "content_block_location"

                            • CitationWebSearchResultLocationParam = object { cited_text, encrypted_index, title, 2 more }

                              • cited_text: string

                              • encrypted_index: string

                              • title: string

                              • type: "web_search_result_location"

                                • "web_search_result_location"

                              • url: string

                            • CitationSearchResultLocationParam = object { cited_text, end_block_index, search_result_index, 4 more }

                              • cited_text: string

                              • end_block_index: number

                              • search_result_index: number

                              • source: string

                              • start_block_index: number

                              • title: string

                              • type: "search_result_location"

                                • "search_result_location"

                        • ImageBlockParam = object { source, type, cache_control }

                          • source: Base64ImageSource or URLImageSource

                            • Base64ImageSource = object { data, media_type, type }

                              • data: string

                              • media_type: "image/jpeg" or "image/png" or "image/gif" or "image/webp"

                                • "image/jpeg"

                                • "image/png"

                                • "image/gif"

                                • "image/webp"

                              • type: "base64"

                                • "base64"

                            • URLImageSource = object { type, url }

                              • type: "url"

                                • "url"

                              • url: string

                          • type: "image"

                            • "image"

                          • cache_control: optional CacheControlEphemeral

                            Create a cache control breakpoint at this content block.

                            • type: "ephemeral"

                              • "ephemeral"

                            • ttl: optional "5m" or "1h"

                              The time-to-live for the cache control breakpoint.

                              This may be one the following values:

                              • 5m: 5 minutes
                              • 1h: 1 hour

                              Defaults to 5m.

                              • "5m"

                              • "1h"

                    • type: "content"

                      • "content"

                  • URLPDFSource = object { type, url }

                    • type: "url"

                      • "url"

                    • url: string

                • type: "document"

                  • "document"

                • cache_control: optional CacheControlEphemeral

                  Create a cache control breakpoint at this content block.

                  • type: "ephemeral"

                    • "ephemeral"

                  • ttl: optional "5m" or "1h"

                    The time-to-live for the cache control breakpoint.

                    This may be one the following values:

                    • 5m: 5 minutes
                    • 1h: 1 hour

                    Defaults to 5m.

                    • "5m"

                    • "1h"

                • citations: optional CitationsConfigParam

                  • enabled: optional boolean

                • context: optional string

                • title: optional string

              • type: "web_fetch_result"

                • "web_fetch_result"

              • url: string

                Fetched content URL

              • retrieved_at: optional string

                ISO 8601 timestamp when the content was retrieved

          • tool_use_id: string

          • type: "web_fetch_tool_result"

            • "web_fetch_tool_result"

          • cache_control: optional CacheControlEphemeral

            Create a cache control breakpoint at this content block.

            • type: "ephemeral"

              • "ephemeral"

            • ttl: optional "5m" or "1h"

              The time-to-live for the cache control breakpoint.

              This may be one the following values:

              • 5m: 5 minutes
              • 1h: 1 hour

              Defaults to 5m.

              • "5m"

              • "1h"

          • caller: optional DirectCaller or ServerToolCaller or ServerToolCaller20260120

            Tool invocation directly from the model.

            • DirectCaller = object { type }

              Tool invocation directly from the model.

              • type: "direct"

                • "direct"

            • ServerToolCaller = object { tool_id, type }

              Tool invocation generated by a server-side tool.

              • tool_id: string

              • type: "code_execution_20250825"

                • "code_execution_20250825"

            • ServerToolCaller20260120 = object { tool_id, type }

              • tool_id: string

              • type: "code_execution_20260120"

                • "code_execution_20260120"

        • CodeExecutionToolResultBlockParam = object { content, tool_use_id, type, cache_control }

          • content: CodeExecutionToolResultBlockParamContent

            Code execution result with encrypted stdout for PFC + web_search results.

            • CodeExecutionToolResultErrorParam = object { error_code, type }

              • error_code: CodeExecutionToolResultErrorCode

                • "invalid_tool_input"

                • "unavailable"

                • "too_many_requests"

                • "execution_time_exceeded"

              • type: "code_execution_tool_result_error"

                • "code_execution_tool_result_error"

            • CodeExecutionResultBlockParam = object { content, return_code, stderr, 2 more }

              • content: array of CodeExecutionOutputBlockParam

                • file_id: string

                • type: "code_execution_output"

                  • "code_execution_output"

              • return_code: number

              • stderr: string

              • stdout: string

              • type: "code_execution_result"

                • "code_execution_result"

            • EncryptedCodeExecutionResultBlockParam = object { content, encrypted_stdout, return_code, 2 more }

              Code execution result with encrypted stdout for PFC + web_search results.

              • content: array of CodeExecutionOutputBlockParam

                • file_id: string

                • type: "code_execution_output"

                  • "code_execution_output"

              • encrypted_stdout: string

              • return_code: number

              • stderr: string

              • type: "encrypted_code_execution_result"

                • "encrypted_code_execution_result"

          • tool_use_id: string

          • type: "code_execution_tool_result"

            • "code_execution_tool_result"

          • cache_control: optional CacheControlEphemeral

            Create a cache control breakpoint at this content block.

            • type: "ephemeral"

              • "ephemeral"

            • ttl: optional "5m" or "1h"

              The time-to-live for the cache control breakpoint.

              This may be one the following values:

              • 5m: 5 minutes
              • 1h: 1 hour

              Defaults to 5m.

              • "5m"

              • "1h"

        • BashCodeExecutionToolResultBlockParam = object { content, tool_use_id, type, cache_control }

          • content: BashCodeExecutionToolResultErrorParam or BashCodeExecutionResultBlockParam

            • BashCodeExecutionToolResultErrorParam = object { error_code, type }

              • error_code: BashCodeExecutionToolResultErrorCode

                • "invalid_tool_input"

                • "unavailable"

                • "too_many_requests"

                • "execution_time_exceeded"

                • "output_file_too_large"

              • type: "bash_code_execution_tool_result_error"

                • "bash_code_execution_tool_result_error"

            • BashCodeExecutionResultBlockParam = object { content, return_code, stderr, 2 more }

              • content: array of BashCodeExecutionOutputBlockParam

                • file_id: string

                • type: "bash_code_execution_output"

                  • "bash_code_execution_output"

              • return_code: number

              • stderr: string

              • stdout: string

              • type: "bash_code_execution_result"

                • "bash_code_execution_result"

          • tool_use_id: string

          • type: "bash_code_execution_tool_result"

            • "bash_code_execution_tool_result"

          • cache_control: optional CacheControlEphemeral

            Create a cache control breakpoint at this content block.

            • type: "ephemeral"

              • "ephemeral"

            • ttl: optional "5m" or "1h"

              The time-to-live for the cache control breakpoint.

              This may be one the following values:

              • 5m: 5 minutes
              • 1h: 1 hour

              Defaults to 5m.

              • "5m"

              • "1h"

        • TextEditorCodeExecutionToolResultBlockParam = object { content, tool_use_id, type, cache_control }

          • content: TextEditorCodeExecutionToolResultErrorParam or TextEditorCodeExecutionViewResultBlockParam or TextEditorCodeExecutionCreateResultBlockParam or TextEditorCodeExecutionStrReplaceResultBlockParam

            • TextEditorCodeExecutionToolResultErrorParam = object { error_code, type, error_message }

              • error_code: TextEditorCodeExecutionToolResultErrorCode

                • "invalid_tool_input"

                • "unavailable"

                • "too_many_requests"

                • "execution_time_exceeded"

                • "file_not_found"

              • type: "text_editor_code_execution_tool_result_error"

                • "text_editor_code_execution_tool_result_error"

              • error_message: optional string

            • TextEditorCodeExecutionViewResultBlockParam = object { content, file_type, type, 3 more }

              • content: string

              • file_type: "text" or "image" or "pdf"

                • "text"

                • "image"

                • "pdf"

              • type: "text_editor_code_execution_view_result"

                • "text_editor_code_execution_view_result"

              • num_lines: optional number

              • start_line: optional number

              • total_lines: optional number

            • TextEditorCodeExecutionCreateResultBlockParam = object { is_file_update, type }

              • is_file_update: boolean

              • type: "text_editor_code_execution_create_result"

                • "text_editor_code_execution_create_result"

            • TextEditorCodeExecutionStrReplaceResultBlockParam = object { type, lines, new_lines, 3 more }

              • type: "text_editor_code_execution_str_replace_result"

                • "text_editor_code_execution_str_replace_result"

              • lines: optional array of string

              • new_lines: optional number

              • new_start: optional number

              • old_lines: optional number

              • old_start: optional number

          • tool_use_id: string

          • type: "text_editor_code_execution_tool_result"

            • "text_editor_code_execution_tool_result"

          • cache_control: optional CacheControlEphemeral

            Create a cache control breakpoint at this content block.

            • type: "ephemeral"

              • "ephemeral"

            • ttl: optional "5m" or "1h"

              The time-to-live for the cache control breakpoint.

              This may be one the following values:

              • 5m: 5 minutes
              • 1h: 1 hour

              Defaults to 5m.

              • "5m"

              • "1h"

        • ToolSearchToolResultBlockParam = object { content, tool_use_id, type, cache_control }

          • content: ToolSearchToolResultErrorParam or ToolSearchToolSearchResultBlockParam

            • ToolSearchToolResultErrorParam = object { error_code, type }

              • error_code: ToolSearchToolResultErrorCode

                • "invalid_tool_input"

                • "unavailable"

                • "too_many_requests"

                • "execution_time_exceeded"

              • type: "tool_search_tool_result_error"

                • "tool_search_tool_result_error"

            • ToolSearchToolSearchResultBlockParam = object { tool_references, type }

              • tool_references: array of ToolReferenceBlockParam

                • tool_name: string

                • type: "tool_reference"

                  • "tool_reference"

                • cache_control: optional CacheControlEphemeral

                  Create a cache control breakpoint at this content block.

                  • type: "ephemeral"

                    • "ephemeral"

                  • ttl: optional "5m" or "1h"

                    The time-to-live for the cache control breakpoint.

                    This may be one the following values:

                    • 5m: 5 minutes
                    • 1h: 1 hour

                    Defaults to 5m.

                    • "5m"

                    • "1h"

              • type: "tool_search_tool_search_result"

                • "tool_search_tool_search_result"

          • tool_use_id: string

          • type: "tool_search_tool_result"

            • "tool_search_tool_result"

          • cache_control: optional CacheControlEphemeral

            Create a cache control breakpoint at this content block.

            • type: "ephemeral"

              • "ephemeral"

            • ttl: optional "5m" or "1h"

              The time-to-live for the cache control breakpoint.

              This may be one the following values:

              • 5m: 5 minutes
              • 1h: 1 hour

              Defaults to 5m.

              • "5m"

              • "1h"

        • ContainerUploadBlockParam = object { file_id, type, cache_control }

          A content block that represents a file to be uploaded to the container Files uploaded via this block will be available in the container's input directory.

          • file_id: string

          • type: "container_upload"

            • "container_upload"

          • cache_control: optional CacheControlEphemeral

            Create a cache control breakpoint at this content block.

            • type: "ephemeral"

              • "ephemeral"

            • ttl: optional "5m" or "1h"

              The time-to-live for the cache control breakpoint.

              This may be one the following values:

              • 5m: 5 minutes
              • 1h: 1 hour

              Defaults to 5m.

              • "5m"

              • "1h"

    • role: "user" or "assistant"

      • "user"

      • "assistant"

  • model: Model

    The model that will complete your prompt.

    See models for additional details and options.

    • UnionMember0 = "claude-opus-4-7" or "claude-mythos-preview" or "claude-opus-4-6" or 14 more

      The model that will complete your prompt.

      See models for additional details and options.

      • "claude-opus-4-7"

        Frontier intelligence for long-running agents and coding

      • "claude-mythos-preview"

        New class of intelligence, strongest in coding and cybersecurity

      • "claude-opus-4-6"

        Frontier intelligence for long-running agents and coding

      • "claude-sonnet-4-6"

        Best combination of speed and intelligence

      • "claude-haiku-4-5"

        Fastest model with near-frontier intelligence

      • "claude-haiku-4-5-20251001"

        Fastest model with near-frontier intelligence

      • "claude-opus-4-5"

        Premium model combining maximum intelligence with practical performance

      • "claude-opus-4-5-20251101"

        Premium model combining maximum intelligence with practical performance

      • "claude-sonnet-4-5"

        High-performance model for agents and coding

      • "claude-sonnet-4-5-20250929"

        High-performance model for agents and coding

      • "claude-opus-4-1"

        Exceptional model for specialized complex tasks

      • "claude-opus-4-1-20250805"

        Exceptional model for specialized complex tasks

      • "claude-opus-4-0"

        Powerful model for complex tasks

      • "claude-opus-4-20250514"

        Powerful model for complex tasks

      • "claude-sonnet-4-0"

        High-performance model with extended thinking

      • "claude-sonnet-4-20250514"

        High-performance model with extended thinking

      • "claude-3-haiku-20240307"

        Fast and cost-effective model

    • UnionMember1 = string

  • cache_control: optional CacheControlEphemeral

    Top-level cache control automatically applies a cache_control marker to the last cacheable block in the request.

    • type: "ephemeral"

      • "ephemeral"

    • ttl: optional "5m" or "1h"

      The time-to-live for the cache control breakpoint.

      This may be one the following values:

      • 5m: 5 minutes
      • 1h: 1 hour

      Defaults to 5m.

      • "5m"

      • "1h"

  • output_config: optional OutputConfig

    Configuration options for the model's output, such as the output format.

    • effort: optional "low" or "medium" or "high" or 2 more

      All possible effort levels.

      • "low"

      • "medium"

      • "high"

      • "xhigh"

      • "max"

    • format: optional JSONOutputFormat

      A schema to specify Claude's output format in responses. See structured outputs

      • schema: map[unknown]

        The JSON schema of the format

      • type: "json_schema"

        • "json_schema"

  • system: optional string or array of TextBlockParam

    System prompt.

    A system prompt is a way of providing context and instructions to Claude, such as specifying a particular goal or role. See our guide to system prompts.

    • UnionMember0 = string

    • UnionMember1 = array of TextBlockParam

      • text: string

      • type: "text"

        • "text"

      • cache_control: optional CacheControlEphemeral

        Create a cache control breakpoint at this content block.

        • type: "ephemeral"

          • "ephemeral"

        • ttl: optional "5m" or "1h"

          The time-to-live for the cache control breakpoint.

          This may be one the following values:

          • 5m: 5 minutes
          • 1h: 1 hour

          Defaults to 5m.

          • "5m"

          • "1h"

      • citations: optional array of TextCitationParam

        • CitationCharLocationParam = object { cited_text, document_index, document_title, 3 more }

          • cited_text: string

          • document_index: number

          • document_title: string

          • end_char_index: number

          • start_char_index: number

          • type: "char_location"

            • "char_location"

        • CitationPageLocationParam = object { cited_text, document_index, document_title, 3 more }

          • cited_text: string

          • document_index: number

          • document_title: string

          • end_page_number: number

          • start_page_number: number

          • type: "page_location"

            • "page_location"

        • CitationContentBlockLocationParam = object { cited_text, document_index, document_title, 3 more }

          • cited_text: string

          • document_index: number

          • document_title: string

          • end_block_index: number

          • start_block_index: number

          • type: "content_block_location"

            • "content_block_location"

        • CitationWebSearchResultLocationParam = object { cited_text, encrypted_index, title, 2 more }

          • cited_text: string

          • encrypted_index: string

          • title: string

          • type: "web_search_result_location"

            • "web_search_result_location"

          • url: string

        • CitationSearchResultLocationParam = object { cited_text, end_block_index, search_result_index, 4 more }

          • cited_text: string

          • end_block_index: number

          • search_result_index: number

          • source: string

          • start_block_index: number

          • title: string

          • type: "search_result_location"

            • "search_result_location"

  • thinking: optional ThinkingConfigParam

    Configuration for enabling Claude's extended thinking.

    When enabled, responses include thinking content blocks showing Claude's thinking process before the final answer. Requires a minimum budget of 1,024 tokens and counts towards your max_tokens limit.

    See extended thinking for details.

    • ThinkingConfigEnabled = object { budget_tokens, type, display }

      • budget_tokens: number

        Determines how many tokens Claude can use for its internal reasoning process. Larger budgets can enable more thorough analysis for complex problems, improving response quality.

        Must be ≥1024 and less than max_tokens.

        See extended thinking for details.

      • type: "enabled"

        • "enabled"

      • display: optional "summarized" or "omitted"

        Controls how thinking content appears in the response. When set to summarized, thinking is returned normally. When set to omitted, thinking content is redacted but a signature is returned for multi-turn continuity. Defaults to summarized.

        • "summarized"

        • "omitted"

    • ThinkingConfigDisabled = object { type }

      • type: "disabled"

        • "disabled"

    • ThinkingConfigAdaptive = object { type, display }

      • type: "adaptive"

        • "adaptive"

      • display: optional "summarized" or "omitted"

        Controls how thinking content appears in the response. When set to summarized, thinking is returned normally. When set to omitted, thinking content is redacted but a signature is returned for multi-turn continuity. Defaults to summarized.

        • "summarized"

        • "omitted"

  • tool_choice: optional ToolChoice

    How the model should use the provided tools. The model can use a specific tool, any available tool, decide by itself, or not use tools at all.

    • ToolChoiceAuto = object { type, disable_parallel_tool_use }

      The model will automatically decide whether to use tools.

      • type: "auto"

        • "auto"

      • disable_parallel_tool_use: optional boolean

        Whether to disable parallel tool use.

        Defaults to false. If set to true, the model will output at most one tool use.

    • ToolChoiceAny = object { type, disable_parallel_tool_use }

      The model will use any available tools.

      • type: "any"

        • "any"

      • disable_parallel_tool_use: optional boolean

        Whether to disable parallel tool use.

        Defaults to false. If set to true, the model will output exactly one tool use.

    • ToolChoiceTool = object { name, type, disable_parallel_tool_use }

      The model will use the specified tool with tool_choice.name.

      • name: string

        The name of the tool to use.

      • type: "tool"

        • "tool"

      • disable_parallel_tool_use: optional boolean

        Whether to disable parallel tool use.

        Defaults to false. If set to true, the model will output exactly one tool use.

    • ToolChoiceNone = object { type }

      The model will not be allowed to use tools.

      • type: "none"

        • "none"

  • tools: optional array of MessageCountTokensTool

    Definitions of tools that the model may use.

    If you include tools in your API request, the model may return tool_use content blocks that represent the model's use of those tools. You can then run those tools using the tool input generated by the model and then optionally return results back to the model using tool_result content blocks.

    There are two types of tools: client tools and server tools. The behavior described below applies to client tools. For server tools, see their individual documentation as each has its own behavior (e.g., the web search tool).

    Each tool definition includes:

    • name: Name of the tool.
    • description: Optional, but strongly-recommended description of the tool.
    • input_schema: JSON schema for the tool input shape that the model will produce in tool_use output content blocks.

    For example, if you defined tools as:

    [
  {
    "name": "get_stock_price",
    "description": "Get the current stock price for a given ticker symbol.",
    "input_schema": {
      "type": "object",
      "properties": {
        "ticker": {
          "type": "string",
          "description": "The stock ticker symbol, e.g. AAPL for Apple Inc."
        }
      },
      "required": ["ticker"]
    }
  }
]

    And then asked the model "What's the S&P 500 at today?", the model might produce tool_use content blocks in the response like this:

    [
  {
    "type": "tool_use",
    "id": "toolu_01D7FLrfh4GYq7yT1ULFeyMV",
    "name": "get_stock_price",
    "input": { "ticker": "^GSPC" }
  }
]

    You might then run your get_stock_price tool with {"ticker": "^GSPC"} as an input, and return the following back to the model in a subsequent user message:

    [
  {
    "type": "tool_result",
    "tool_use_id": "toolu_01D7FLrfh4GYq7yT1ULFeyMV",
    "content": "259.75 USD"
  }
]

    Tools can be used for workflows that include running client-side tools and functions, or more generally whenever you want the model to produce a particular JSON structure of output.

    See our guide for more details.

    • Tool = object { input_schema, name, allowed_callers, 7 more }

      • input_schema: object { type, properties, required }

        JSON schema for this tool's input.

        This defines the shape of the input that your tool accepts and that the model will produce.

        • type: "object"

          • "object"

        • properties: optional map[unknown]

        • required: optional array of string

      • name: string

        Name of the tool.

        This is how the tool will be called by the model and in tool_use blocks.

      • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"

        • "direct"

        • "code_execution_20250825"

        • "code_execution_20260120"

      • cache_control: optional CacheControlEphemeral

        Create a cache control breakpoint at this content block.

        • type: "ephemeral"

          • "ephemeral"

        • ttl: optional "5m" or "1h"

          The time-to-live for the cache control breakpoint.

          This may be one the following values:

          • 5m: 5 minutes
          • 1h: 1 hour

          Defaults to 5m.

          • "5m"

          • "1h"

      • defer_loading: optional boolean

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      • description: optional string

        Description of what this tool does.

        Tool descriptions should be as detailed as possible. The more information that the model has about what the tool is and how to use it, the better it will perform. You can use natural language descriptions to reinforce important aspects of the tool input JSON schema.

      • eager_input_streaming: optional boolean

        Enable eager input streaming for this tool. When true, tool input parameters will be streamed incrementally as they are generated, and types will be inferred on-the-fly rather than buffering the full JSON output. When false, streaming is disabled for this tool even if the fine-grained-tool-streaming beta is active. When null (default), uses the default behavior based on beta headers.

      • input_examples: optional array of map[unknown]

      • strict: optional boolean

        When true, guarantees schema validation on tool names and inputs

      • type: optional "custom"

        • "custom"

    • ToolBash20250124 = object { name, type, allowed_callers, 4 more }

      • name: "bash"

        Name of the tool.

        This is how the tool will be called by the model and in tool_use blocks.

        • "bash"

      • type: "bash_20250124"

        • "bash_20250124"

      • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"

        • "direct"

        • "code_execution_20250825"

        • "code_execution_20260120"

      • cache_control: optional CacheControlEphemeral

        Create a cache control breakpoint at this content block.

        • type: "ephemeral"

          • "ephemeral"

        • ttl: optional "5m" or "1h"

          The time-to-live for the cache control breakpoint.

          This may be one the following values:

          • 5m: 5 minutes
          • 1h: 1 hour

          Defaults to 5m.

          • "5m"

          • "1h"

      • defer_loading: optional boolean

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      • input_examples: optional array of map[unknown]

      • strict: optional boolean

        When true, guarantees schema validation on tool names and inputs

    • CodeExecutionTool20250522 = object { name, type, allowed_callers, 3 more }

      • name: "code_execution"

        Name of the tool.

        This is how the tool will be called by the model and in tool_use blocks.

        • "code_execution"

      • type: "code_execution_20250522"

        • "code_execution_20250522"

      • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"

        • "direct"

        • "code_execution_20250825"

        • "code_execution_20260120"

      • cache_control: optional CacheControlEphemeral

        Create a cache control breakpoint at this content block.

        • type: "ephemeral"

          • "ephemeral"

        • ttl: optional "5m" or "1h"

          The time-to-live for the cache control breakpoint.

          This may be one the following values:

          • 5m: 5 minutes
          • 1h: 1 hour

          Defaults to 5m.

          • "5m"

          • "1h"

      • defer_loading: optional boolean

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      • strict: optional boolean

        When true, guarantees schema validation on tool names and inputs

    • CodeExecutionTool20250825 = object { name, type, allowed_callers, 3 more }

      • name: "code_execution"

        Name of the tool.

        This is how the tool will be called by the model and in tool_use blocks.

        • "code_execution"

      • type: "code_execution_20250825"

        • "code_execution_20250825"

      • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"

        • "direct"

        • "code_execution_20250825"

        • "code_execution_20260120"

      • cache_control: optional CacheControlEphemeral

        Create a cache control breakpoint at this content block.

        • type: "ephemeral"

          • "ephemeral"

        • ttl: optional "5m" or "1h"

          The time-to-live for the cache control breakpoint.

          This may be one the following values:

          • 5m: 5 minutes
          • 1h: 1 hour

          Defaults to 5m.

          • "5m"

          • "1h"

      • defer_loading: optional boolean

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      • strict: optional boolean

        When true, guarantees schema validation on tool names and inputs

    • CodeExecutionTool20260120 = object { name, type, allowed_callers, 3 more }

      Code execution tool with REPL state persistence (daemon mode + gVisor checkpoint).

      • name: "code_execution"

        Name of the tool.

        This is how the tool will be called by the model and in tool_use blocks.

        • "code_execution"

      • type: "code_execution_20260120"

        • "code_execution_20260120"

      • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"

        • "direct"

        • "code_execution_20250825"

        • "code_execution_20260120"

      • cache_control: optional CacheControlEphemeral

        Create a cache control breakpoint at this content block.

        • type: "ephemeral"

          • "ephemeral"

        • ttl: optional "5m" or "1h"

          The time-to-live for the cache control breakpoint.

          This may be one the following values:

          • 5m: 5 minutes
          • 1h: 1 hour

          Defaults to 5m.

          • "5m"

          • "1h"

      • defer_loading: optional boolean

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      • strict: optional boolean

        When true, guarantees schema validation on tool names and inputs

    • MemoryTool20250818 = object { name, type, allowed_callers, 4 more }

      • name: "memory"

        Name of the tool.

        This is how the tool will be called by the model and in tool_use blocks.

        • "memory"

      • type: "memory_20250818"

        • "memory_20250818"

      • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"

        • "direct"

        • "code_execution_20250825"

        • "code_execution_20260120"

      • cache_control: optional CacheControlEphemeral

        Create a cache control breakpoint at this content block.

        • type: "ephemeral"

          • "ephemeral"

        • ttl: optional "5m" or "1h"

          The time-to-live for the cache control breakpoint.

          This may be one the following values:

          • 5m: 5 minutes
          • 1h: 1 hour

          Defaults to 5m.

          • "5m"

          • "1h"

      • defer_loading: optional boolean

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      • input_examples: optional array of map[unknown]

      • strict: optional boolean

        When true, guarantees schema validation on tool names and inputs

    • ToolTextEditor20250124 = object { name, type, allowed_callers, 4 more }

      • name: "str_replace_editor"

        Name of the tool.

        This is how the tool will be called by the model and in tool_use blocks.

        • "str_replace_editor"

      • type: "text_editor_20250124"

        • "text_editor_20250124"

      • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"

        • "direct"

        • "code_execution_20250825"

        • "code_execution_20260120"

      • cache_control: optional CacheControlEphemeral

        Create a cache control breakpoint at this content block.

        • type: "ephemeral"

          • "ephemeral"

        • ttl: optional "5m" or "1h"

          The time-to-live for the cache control breakpoint.

          This may be one the following values:

          • 5m: 5 minutes
          • 1h: 1 hour

          Defaults to 5m.

          • "5m"

          • "1h"

      • defer_loading: optional boolean

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      • input_examples: optional array of map[unknown]

      • strict: optional boolean

        When true, guarantees schema validation on tool names and inputs

    • ToolTextEditor20250429 = object { name, type, allowed_callers, 4 more }

      • name: "str_replace_based_edit_tool"

        Name of the tool.

        This is how the tool will be called by the model and in tool_use blocks.

        • "str_replace_based_edit_tool"

      • type: "text_editor_20250429"

        • "text_editor_20250429"

      • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"

        • "direct"

        • "code_execution_20250825"

        • "code_execution_20260120"

      • cache_control: optional CacheControlEphemeral

        Create a cache control breakpoint at this content block.

        • type: "ephemeral"

          • "ephemeral"

        • ttl: optional "5m" or "1h"

          The time-to-live for the cache control breakpoint.

          This may be one the following values:

          • 5m: 5 minutes
          • 1h: 1 hour

          Defaults to 5m.

          • "5m"

          • "1h"

      • defer_loading: optional boolean

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      • input_examples: optional array of map[unknown]

      • strict: optional boolean

        When true, guarantees schema validation on tool names and inputs

    • ToolTextEditor20250728 = object { name, type, allowed_callers, 5 more }

      • name: "str_replace_based_edit_tool"

        Name of the tool.

        This is how the tool will be called by the model and in tool_use blocks.

        • "str_replace_based_edit_tool"

      • type: "text_editor_20250728"

        • "text_editor_20250728"

      • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"

        • "direct"

        • "code_execution_20250825"

        • "code_execution_20260120"

      • cache_control: optional CacheControlEphemeral

        Create a cache control breakpoint at this content block.

        • type: "ephemeral"

          • "ephemeral"

        • ttl: optional "5m" or "1h"

          The time-to-live for the cache control breakpoint.

          This may be one the following values:

          • 5m: 5 minutes
          • 1h: 1 hour

          Defaults to 5m.

          • "5m"

          • "1h"

      • defer_loading: optional boolean

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      • input_examples: optional array of map[unknown]

      • max_characters: optional number

        Maximum number of characters to display when viewing a file. If not specified, defaults to displaying the full file.

      • strict: optional boolean

        When true, guarantees schema validation on tool names and inputs

    • WebSearchTool20250305 = object { name, type, allowed_callers, 7 more }

      • name: "web_search"

        Name of the tool.

        This is how the tool will be called by the model and in tool_use blocks.

        • "web_search"

      • type: "web_search_20250305"

        • "web_search_20250305"

      • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"

        • "direct"

        • "code_execution_20250825"

        • "code_execution_20260120"

      • allowed_domains: optional array of string

        If provided, only these domains will be included in results. Cannot be used alongside blocked_domains.

      • blocked_domains: optional array of string

        If provided, these domains will never appear in results. Cannot be used alongside allowed_domains.

      • cache_control: optional CacheControlEphemeral

        Create a cache control breakpoint at this content block.

        • type: "ephemeral"

          • "ephemeral"

        • ttl: optional "5m" or "1h"

          The time-to-live for the cache control breakpoint.

          This may be one the following values:

          • 5m: 5 minutes
          • 1h: 1 hour

          Defaults to 5m.

          • "5m"

          • "1h"

      • defer_loading: optional boolean

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      • max_uses: optional number

        Maximum number of times the tool can be used in the API request.

      • strict: optional boolean

        When true, guarantees schema validation on tool names and inputs

      • user_location: optional UserLocation

        Parameters for the user's location. Used to provide more relevant search results.

        • type: "approximate"

          • "approximate"

        • city: optional string

          The city of the user.

        • country: optional string

          The two letter ISO country code of the user.

        • region: optional string

          The region of the user.

        • timezone: optional string

          The IANA timezone of the user.

    • WebFetchTool20250910 = object { name, type, allowed_callers, 8 more }

      • name: "web_fetch"

        Name of the tool.

        This is how the tool will be called by the model and in tool_use blocks.

        • "web_fetch"

      • type: "web_fetch_20250910"

        • "web_fetch_20250910"

      • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"

        • "direct"

        • "code_execution_20250825"

        • "code_execution_20260120"

      • allowed_domains: optional array of string

        List of domains to allow fetching from

      • blocked_domains: optional array of string

        List of domains to block fetching from

      • cache_control: optional CacheControlEphemeral

        Create a cache control breakpoint at this content block.

        • type: "ephemeral"

          • "ephemeral"

        • ttl: optional "5m" or "1h"

          The time-to-live for the cache control breakpoint.

          This may be one the following values:

          • 5m: 5 minutes
          • 1h: 1 hour

          Defaults to 5m.

          • "5m"

          • "1h"

      • citations: optional CitationsConfigParam

        Citations configuration for fetched documents. Citations are disabled by default.

        • enabled: optional boolean

      • defer_loading: optional boolean

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      • max_content_tokens: optional number

        Maximum number of tokens used by including web page text content in the context. The limit is approximate and does not apply to binary content such as PDFs.

      • max_uses: optional number

        Maximum number of times the tool can be used in the API request.

      • strict: optional boolean

        When true, guarantees schema validation on tool names and inputs

    • WebSearchTool20260209 = object { name, type, allowed_callers, 7 more }

      • name: "web_search"

        Name of the tool.

        This is how the tool will be called by the model and in tool_use blocks.

        • "web_search"

      • type: "web_search_20260209"

        • "web_search_20260209"

      • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"

        • "direct"

        • "code_execution_20250825"

        • "code_execution_20260120"

      • allowed_domains: optional array of string

        If provided, only these domains will be included in results. Cannot be used alongside blocked_domains.

      • blocked_domains: optional array of string

        If provided, these domains will never appear in results. Cannot be used alongside allowed_domains.

      • cache_control: optional CacheControlEphemeral

        Create a cache control breakpoint at this content block.

        • type: "ephemeral"

          • "ephemeral"

        • ttl: optional "5m" or "1h"

          The time-to-live for the cache control breakpoint.

          This may be one the following values:

          • 5m: 5 minutes
          • 1h: 1 hour

          Defaults to 5m.

          • "5m"

          • "1h"

      • defer_loading: optional boolean

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      • max_uses: optional number

        Maximum number of times the tool can be used in the API request.

      • strict: optional boolean

        When true, guarantees schema validation on tool names and inputs

      • user_location: optional UserLocation

        Parameters for the user's location. Used to provide more relevant search results.

        • type: "approximate"

          • "approximate"

        • city: optional string

          The city of the user.

        • country: optional string

          The two letter ISO country code of the user.

        • region: optional string

          The region of the user.

        • timezone: optional string

          The IANA timezone of the user.

    • WebFetchTool20260209 = object { name, type, allowed_callers, 8 more }

      • name: "web_fetch"

        Name of the tool.

        This is how the tool will be called by the model and in tool_use blocks.

        • "web_fetch"

      • type: "web_fetch_20260209"

        • "web_fetch_20260209"

      • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"

        • "direct"

        • "code_execution_20250825"

        • "code_execution_20260120"

      • allowed_domains: optional array of string

        List of domains to allow fetching from

      • blocked_domains: optional array of string

        List of domains to block fetching from

      • cache_control: optional CacheControlEphemeral

        Create a cache control breakpoint at this content block.

        • type: "ephemeral"

          • "ephemeral"

        • ttl: optional "5m" or "1h"

          The time-to-live for the cache control breakpoint.

          This may be one the following values:

          • 5m: 5 minutes
          • 1h: 1 hour

          Defaults to 5m.

          • "5m"

          • "1h"

      • citations: optional CitationsConfigParam

        Citations configuration for fetched documents. Citations are disabled by default.

        • enabled: optional boolean

      • defer_loading: optional boolean

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      • max_content_tokens: optional number

        Maximum number of tokens used by including web page text content in the context. The limit is approximate and does not apply to binary content such as PDFs.

      • max_uses: optional number

        Maximum number of times the tool can be used in the API request.

      • strict: optional boolean

        When true, guarantees schema validation on tool names and inputs

    • WebFetchTool20260309 = object { name, type, allowed_callers, 9 more }

      Web fetch tool with use_cache parameter for bypassing cached content.

      • name: "web_fetch"

        Name of the tool.

        This is how the tool will be called by the model and in tool_use blocks.

        • "web_fetch"

      • type: "web_fetch_20260309"

        • "web_fetch_20260309"

      • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"

        • "direct"

        • "code_execution_20250825"

        • "code_execution_20260120"

      • allowed_domains: optional array of string

        List of domains to allow fetching from

      • blocked_domains: optional array of string

        List of domains to block fetching from

      • cache_control: optional CacheControlEphemeral

        Create a cache control breakpoint at this content block.

        • type: "ephemeral"

          • "ephemeral"

        • ttl: optional "5m" or "1h"

          The time-to-live for the cache control breakpoint.

          This may be one the following values:

          • 5m: 5 minutes
          • 1h: 1 hour

          Defaults to 5m.

          • "5m"

          • "1h"

      • citations: optional CitationsConfigParam

        Citations configuration for fetched documents. Citations are disabled by default.

        • enabled: optional boolean

      • defer_loading: optional boolean

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      • max_content_tokens: optional number

        Maximum number of tokens used by including web page text content in the context. The limit is approximate and does not apply to binary content such as PDFs.

      • max_uses: optional number

        Maximum number of times the tool can be used in the API request.

      • strict: optional boolean

        When true, guarantees schema validation on tool names and inputs

      • use_cache: optional boolean

        Whether to use cached content. Set to false to bypass the cache and fetch fresh content. Only set to false when the user explicitly requests fresh content or when fetching rapidly-changing sources.

    • ToolSearchToolBm25_20251119 = object { name, type, allowed_callers, 3 more }

      • name: "tool_search_tool_bm25"

        Name of the tool.

        This is how the tool will be called by the model and in tool_use blocks.

        • "tool_search_tool_bm25"

      • type: "tool_search_tool_bm25_20251119" or "tool_search_tool_bm25"

        • "tool_search_tool_bm25_20251119"

        • "tool_search_tool_bm25"

      • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"

        • "direct"

        • "code_execution_20250825"

        • "code_execution_20260120"

      • cache_control: optional CacheControlEphemeral

        Create a cache control breakpoint at this content block.

        • type: "ephemeral"

          • "ephemeral"

        • ttl: optional "5m" or "1h"

          The time-to-live for the cache control breakpoint.

          This may be one the following values:

          • 5m: 5 minutes
          • 1h: 1 hour

          Defaults to 5m.

          • "5m"

          • "1h"

      • defer_loading: optional boolean

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      • strict: optional boolean

        When true, guarantees schema validation on tool names and inputs

    • ToolSearchToolRegex20251119 = object { name, type, allowed_callers, 3 more }

      • name: "tool_search_tool_regex"

        Name of the tool.

        This is how the tool will be called by the model and in tool_use blocks.

        • "tool_search_tool_regex"

      • type: "tool_search_tool_regex_20251119" or "tool_search_tool_regex"

        • "tool_search_tool_regex_20251119"

        • "tool_search_tool_regex"

      • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120"

        • "direct"

        • "code_execution_20250825"

        • "code_execution_20260120"

      • cache_control: optional CacheControlEphemeral

        Create a cache control breakpoint at this content block.

        • type: "ephemeral"

          • "ephemeral"

        • ttl: optional "5m" or "1h"

          The time-to-live for the cache control breakpoint.

          This may be one the following values:

          • 5m: 5 minutes
          • 1h: 1 hour

          Defaults to 5m.

          • "5m"

          • "1h"

      • defer_loading: optional boolean

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      • strict: optional boolean

        When true, guarantees schema validation on tool names and inputs

Returns

  • MessageTokensCount = object { input_tokens }

    • input_tokens: number

      The total number of tokens across the provided list of messages, system prompt, and tools.

Example

curl https://api.anthropic.com/v1/messages/count_tokens \
    -H 'Content-Type: application/json' \
    -H 'anthropic-version: 2023-06-01' \
    -H "X-Api-Key: $ANTHROPIC_API_KEY" \
    -d '{
          "messages": [
            {
              "content": "Hello, world",
              "role": "user"
            }
          ],
          "model": "claude-opus-4-6"
        }'
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