Count tokens in a Message

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

Header Parameters

• "anthropic-beta": optional array of AnthropicBeta

  Optional header to specify the beta version(s) you want to use.

  • string

  • "message-batches-2024-09-24" or "prompt-caching-2024-07-31" or "computer-use-2024-10-22" or 22 more

    • "message-batches-2024-09-24"

    • "prompt-caching-2024-07-31"

    • "computer-use-2024-10-22"

    • "computer-use-2025-01-24"

    • "pdfs-2024-09-25"

    • "token-counting-2024-11-01"

    • "token-efficient-tools-2025-02-19"

    • "output-128k-2025-02-19"

    • "files-api-2025-04-14"

    • "mcp-client-2025-04-04"

    • "mcp-client-2025-11-20"

    • "dev-full-thinking-2025-05-14"

    • "interleaved-thinking-2025-05-14"

    • "code-execution-2025-05-22"

    • "extended-cache-ttl-2025-04-11"

    • "context-1m-2025-08-07"

    • "context-management-2025-06-27"

    • "model-context-window-exceeded-2025-08-26"

    • "skills-2025-10-02"

    • "fast-mode-2026-02-01"

    • "output-300k-2026-03-24"

    • "user-profiles-2026-03-24"

    • "advisor-tool-2026-03-01"

    • "managed-agents-2026-04-01"

    • "cache-diagnosis-2026-04-07"

Body Parameters

• messages: array of BetaMessageParam

  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 BetaContentBlockParam

    • string

    • array of BetaContentBlockParam

      • BetaTextBlockParam object { text, type, cache_control, citations }

        • text: string

        • type: "text"

          • "text"

        • cache_control: optional BetaCacheControlEphemeral

          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 BetaTextCitationParam

          • BetaCitationCharLocationParam 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"

          • BetaCitationPageLocationParam 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"

          • BetaCitationContentBlockLocationParam object { cited_text, document_index, document_title, 3 more }

            • cited_text: string

              The full text of the cited block range, concatenated.

              Always equals the contents of content[start_block_index:end_block_index] joined together. The text block is the minimal citable unit; this field is never a substring of a single block. Not counted toward output tokens, and not counted toward input tokens when sent back in subsequent turns.

            • document_index: number

            • document_title: string

            • end_block_index: number

              Exclusive 0-based end index of the cited block range in the source's content array.

              Always greater than start_block_index; a single-block citation has end_block_index = start_block_index + 1.

            • start_block_index: number

              0-based index of the first cited block in the source's content array.

            • type: "content_block_location"

              • "content_block_location"

          • BetaCitationWebSearchResultLocationParam 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

          • BetaCitationSearchResultLocationParam object { cited_text, end_block_index, search_result_index, 4 more }

            • cited_text: string

              The full text of the cited block range, concatenated.

              Always equals the contents of content[start_block_index:end_block_index] joined together. The text block is the minimal citable unit; this field is never a substring of a single block. Not counted toward output tokens, and not counted toward input tokens when sent back in subsequent turns.

            • end_block_index: number

              Exclusive 0-based end index of the cited block range in the source's content array.

              Always greater than start_block_index; a single-block citation has end_block_index = start_block_index + 1.

            • search_result_index: number

              0-based index of the cited search result among all search_result content blocks in the request, in the order they appear across messages and tool results.

              Counted separately from document_index; server-side web search results are not included in this count.

            • source: string

            • start_block_index: number

              0-based index of the first cited block in the source's content array.

            • title: string

            • type: "search_result_location"

              • "search_result_location"

      • BetaImageBlockParam object { source, type, cache_control }

        • source: BetaBase64ImageSource or BetaURLImageSource or BetaFileImageSource

          • BetaBase64ImageSource 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"

          • BetaURLImageSource object { type, url }

            • type: "url"

              • "url"

            • url: string

          • BetaFileImageSource object { file_id, type }

            • file_id: string

            • type: "file"

              • "file"

        • type: "image"

          • "image"

        • cache_control: optional BetaCacheControlEphemeral

          Create a cache control breakpoint at this content block.

      • BetaRequestDocumentBlock object { source, type, cache_control, 3 more }

        • source: BetaBase64PDFSource or BetaPlainTextSource or BetaContentBlockSource or 2 more

          • BetaBase64PDFSource object { data, media_type, type }

            • data: string

            • media_type: "application/pdf"

              • "application/pdf"

            • type: "base64"

              • "base64"

          • BetaPlainTextSource object { data, media_type, type }

            • data: string

            • media_type: "text/plain"

              • "text/plain"

            • type: "text"

              • "text"

          • BetaContentBlockSource object { content, type }

            • content: string or array of BetaContentBlockSourceContent

              • string

              • BetaContentBlockSourceContent = array of BetaContentBlockSourceContent

                • BetaTextBlockParam object { text, type, cache_control, citations }

                • BetaImageBlockParam object { source, type, cache_control }

            • type: "content"

              • "content"

          • BetaURLPDFSource object { type, url }

            • type: "url"

              • "url"

            • url: string

          • BetaFileDocumentSource object { file_id, type }

            • file_id: string

            • type: "file"

              • "file"

        • type: "document"

          • "document"

        • cache_control: optional BetaCacheControlEphemeral

          Create a cache control breakpoint at this content block.

        • citations: optional BetaCitationsConfigParam

          • enabled: optional boolean

        • context: optional string

        • title: optional string

      • BetaSearchResultBlockParam object { content, source, title, 3 more }

        • content: array of BetaTextBlockParam

          • text: string

          • type: "text"

          • cache_control: optional BetaCacheControlEphemeral

            Create a cache control breakpoint at this content block.

          • citations: optional array of BetaTextCitationParam

        • source: string

        • title: string

        • type: "search_result"

          • "search_result"

        • cache_control: optional BetaCacheControlEphemeral

          Create a cache control breakpoint at this content block.

        • citations: optional BetaCitationsConfigParam

      • BetaThinkingBlockParam object { signature, thinking, type }

        • signature: string

        • thinking: string

        • type: "thinking"

          • "thinking"

      • BetaRedactedThinkingBlockParam object { data, type }

        • data: string

        • type: "redacted_thinking"

          • "redacted_thinking"

      • BetaToolUseBlockParam object { id, input, name, 3 more }

        • id: string

        • input: map[unknown]

        • name: string

        • type: "tool_use"

          • "tool_use"

        • cache_control: optional BetaCacheControlEphemeral

          Create a cache control breakpoint at this content block.

        • caller: optional BetaDirectCaller or BetaServerToolCaller or BetaServerToolCaller20260120

          Tool invocation directly from the model.

          • BetaDirectCaller object { type }

            Tool invocation directly from the model.

            • type: "direct"

              • "direct"

          • BetaServerToolCaller object { tool_id, type }

            Tool invocation generated by a server-side tool.

            • tool_id: string

            • type: "code_execution_20250825"

              • "code_execution_20250825"

          • BetaServerToolCaller20260120 object { tool_id, type }

            • tool_id: string

            • type: "code_execution_20260120"

              • "code_execution_20260120"

      • BetaToolResultBlockParam object { tool_use_id, type, cache_control, 2 more }

        • tool_use_id: string

        • type: "tool_result"

          • "tool_result"

        • cache_control: optional BetaCacheControlEphemeral

          Create a cache control breakpoint at this content block.

        • content: optional string or array of BetaTextBlockParam or BetaImageBlockParam or BetaSearchResultBlockParam or 2 more

          • string

          • array of BetaTextBlockParam or BetaImageBlockParam or BetaSearchResultBlockParam or 2 more

            • BetaTextBlockParam object { text, type, cache_control, citations }

            • BetaImageBlockParam object { source, type, cache_control }

            • BetaSearchResultBlockParam object { content, source, title, 3 more }

            • BetaRequestDocumentBlock object { source, type, cache_control, 3 more }

            • BetaToolReferenceBlockParam 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 BetaCacheControlEphemeral

                Create a cache control breakpoint at this content block.

        • is_error: optional boolean

      • BetaServerToolUseBlockParam object { id, input, name, 3 more }

        • id: string

        • input: map[unknown]

        • name: "advisor" or "web_search" or "web_fetch" or 5 more

          • "advisor"

          • "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 BetaCacheControlEphemeral

          Create a cache control breakpoint at this content block.

        • caller: optional BetaDirectCaller or BetaServerToolCaller or BetaServerToolCaller20260120

          Tool invocation directly from the model.

          • BetaDirectCaller object { type }

            Tool invocation directly from the model.

          • BetaServerToolCaller object { tool_id, type }

            Tool invocation generated by a server-side tool.

          • BetaServerToolCaller20260120 object { tool_id, type }

      • BetaWebSearchToolResultBlockParam object { content, tool_use_id, type, 2 more }

        • content: BetaWebSearchToolResultBlockParamContent

          • ResultBlock = array of BetaWebSearchResultBlockParam

            • encrypted_content: string

            • title: string

            • type: "web_search_result"

              • "web_search_result"

            • url: string

            • page_age: optional string

          • BetaWebSearchToolRequestError object { error_code, type }

            • error_code: BetaWebSearchToolResultErrorCode

              • "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 BetaCacheControlEphemeral

          Create a cache control breakpoint at this content block.

        • caller: optional BetaDirectCaller or BetaServerToolCaller or BetaServerToolCaller20260120

          Tool invocation directly from the model.

          • BetaDirectCaller object { type }

            Tool invocation directly from the model.

          • BetaServerToolCaller object { tool_id, type }

            Tool invocation generated by a server-side tool.

          • BetaServerToolCaller20260120 object { tool_id, type }

      • BetaWebFetchToolResultBlockParam object { content, tool_use_id, type, 2 more }

        • content: BetaWebFetchToolResultErrorBlockParam or BetaWebFetchBlockParam

          • BetaWebFetchToolResultErrorBlockParam object { error_code, type }

            • error_code: BetaWebFetchToolResultErrorCode

              • "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"

          • BetaWebFetchBlockParam object { content, type, url, retrieved_at }

            • content: BetaRequestDocumentBlock

            • 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 BetaCacheControlEphemeral

          Create a cache control breakpoint at this content block.

        • caller: optional BetaDirectCaller or BetaServerToolCaller or BetaServerToolCaller20260120

          Tool invocation directly from the model.

          • BetaDirectCaller object { type }

            Tool invocation directly from the model.

          • BetaServerToolCaller object { tool_id, type }

            Tool invocation generated by a server-side tool.

          • BetaServerToolCaller20260120 object { tool_id, type }

      • BetaAdvisorToolResultBlockParam object { content, tool_use_id, type, cache_control }

        • content: BetaAdvisorToolResultErrorParam or BetaAdvisorResultBlockParam or BetaAdvisorRedactedResultBlockParam

          • BetaAdvisorToolResultErrorParam object { error_code, type }

            • error_code: "max_uses_exceeded" or "prompt_too_long" or "too_many_requests" or 3 more

              • "max_uses_exceeded"

              • "prompt_too_long"

              • "too_many_requests"

              • "overloaded"

              • "unavailable"

              • "execution_time_exceeded"

            • type: "advisor_tool_result_error"

              • "advisor_tool_result_error"

          • BetaAdvisorResultBlockParam object { text, type }

            • text: string

            • type: "advisor_result"

              • "advisor_result"

          • BetaAdvisorRedactedResultBlockParam object { encrypted_content, type }

            • encrypted_content: string

              Opaque blob produced by a prior response; must be round-tripped verbatim.

            • type: "advisor_redacted_result"

              • "advisor_redacted_result"

        • tool_use_id: string

        • type: "advisor_tool_result"

          • "advisor_tool_result"

        • cache_control: optional BetaCacheControlEphemeral

          Create a cache control breakpoint at this content block.

      • BetaCodeExecutionToolResultBlockParam object { content, tool_use_id, type, cache_control }

        • content: BetaCodeExecutionToolResultBlockParamContent

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

          • BetaCodeExecutionToolResultErrorParam object { error_code, type }

            • error_code: BetaCodeExecutionToolResultErrorCode

              • "invalid_tool_input"

              • "unavailable"

              • "too_many_requests"

              • "execution_time_exceeded"

            • type: "code_execution_tool_result_error"

              • "code_execution_tool_result_error"

          • BetaCodeExecutionResultBlockParam object { content, return_code, stderr, 2 more }

            • content: array of BetaCodeExecutionOutputBlockParam

              • file_id: string

              • type: "code_execution_output"

                • "code_execution_output"

            • return_code: number

            • stderr: string

            • stdout: string

            • type: "code_execution_result"

              • "code_execution_result"

          • BetaEncryptedCodeExecutionResultBlockParam object { content, encrypted_stdout, return_code, 2 more }

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

            • content: array of BetaCodeExecutionOutputBlockParam

              • file_id: string

              • type: "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 BetaCacheControlEphemeral

          Create a cache control breakpoint at this content block.

      • BetaBashCodeExecutionToolResultBlockParam object { content, tool_use_id, type, cache_control }

        • content: BetaBashCodeExecutionToolResultErrorParam or BetaBashCodeExecutionResultBlockParam

          • BetaBashCodeExecutionToolResultErrorParam object { error_code, type }

            • error_code: "invalid_tool_input" or "unavailable" or "too_many_requests" or 2 more

              • "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"

          • BetaBashCodeExecutionResultBlockParam object { content, return_code, stderr, 2 more }

            • content: array of BetaBashCodeExecutionOutputBlockParam

              • 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 BetaCacheControlEphemeral

          Create a cache control breakpoint at this content block.

      • BetaTextEditorCodeExecutionToolResultBlockParam object { content, tool_use_id, type, cache_control }

        • content: BetaTextEditorCodeExecutionToolResultErrorParam or BetaTextEditorCodeExecutionViewResultBlockParam or BetaTextEditorCodeExecutionCreateResultBlockParam or BetaTextEditorCodeExecutionStrReplaceResultBlockParam

          • BetaTextEditorCodeExecutionToolResultErrorParam object { error_code, type, error_message }

            • error_code: "invalid_tool_input" or "unavailable" or "too_many_requests" or 2 more

              • "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

          • BetaTextEditorCodeExecutionViewResultBlockParam 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

          • BetaTextEditorCodeExecutionCreateResultBlockParam object { is_file_update, type }

            • is_file_update: boolean

            • type: "text_editor_code_execution_create_result"

              • "text_editor_code_execution_create_result"

          • BetaTextEditorCodeExecutionStrReplaceResultBlockParam 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 BetaCacheControlEphemeral

          Create a cache control breakpoint at this content block.

      • BetaToolSearchToolResultBlockParam object { content, tool_use_id, type, cache_control }

        • content: BetaToolSearchToolResultErrorParam or BetaToolSearchToolSearchResultBlockParam

          • BetaToolSearchToolResultErrorParam object { error_code, type }

            • error_code: "invalid_tool_input" or "unavailable" or "too_many_requests" or "execution_time_exceeded"

              • "invalid_tool_input"

              • "unavailable"

              • "too_many_requests"

              • "execution_time_exceeded"

            • type: "tool_search_tool_result_error"

              • "tool_search_tool_result_error"

          • BetaToolSearchToolSearchResultBlockParam object { tool_references, type }

            • tool_references: array of BetaToolReferenceBlockParam

              • tool_name: string

              • type: "tool_reference"

              • cache_control: optional BetaCacheControlEphemeral

                Create a cache control breakpoint at this content block.

            • 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 BetaCacheControlEphemeral

          Create a cache control breakpoint at this content block.

      • BetaMCPToolUseBlockParam object { id, input, name, 3 more }

        • id: string

        • input: map[unknown]

        • name: string

        • server_name: string

          The name of the MCP server

        • type: "mcp_tool_use"

          • "mcp_tool_use"

        • cache_control: optional BetaCacheControlEphemeral

          Create a cache control breakpoint at this content block.

      • BetaRequestMCPToolResultBlockParam object { tool_use_id, type, cache_control, 2 more }

        • tool_use_id: string

        • type: "mcp_tool_result"

          • "mcp_tool_result"

        • cache_control: optional BetaCacheControlEphemeral

          Create a cache control breakpoint at this content block.

        • content: optional string or array of BetaTextBlockParam

          • string

          • BetaMCPToolResultBlockParamContent = array of BetaTextBlockParam

            • text: string

            • type: "text"

            • cache_control: optional BetaCacheControlEphemeral

              Create a cache control breakpoint at this content block.

            • citations: optional array of BetaTextCitationParam

        • is_error: optional boolean

      • BetaContainerUploadBlockParam 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 BetaCacheControlEphemeral

          Create a cache control breakpoint at this content block.

      • BetaCompactionBlockParam object { content, type, cache_control, encrypted_content }

        A compaction block containing summary of previous context.

        Users should round-trip these blocks from responses to subsequent requests to maintain context across compaction boundaries.

        When content is None, the block represents a failed compaction. The server treats these as no-ops. Empty string content is not allowed.

        • content: string

          Summary of previously compacted content, or null if compaction failed

        • type: "compaction"

          • "compaction"

        • cache_control: optional BetaCacheControlEphemeral

          Create a cache control breakpoint at this content block.

        • encrypted_content: optional string

          Opaque metadata from prior compaction, to be round-tripped verbatim

  • role: "user" or "assistant"

    • "user"

    • "assistant"

• model: Model

  The model that will complete your prompt.

  See models for additional details and options.

  • "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

  • string

• cache_control: optional BetaCacheControlEphemeral

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

• context_management: optional BetaContextManagementConfig

  Context management configuration.

  This allows you to control how Claude manages context across multiple requests, such as whether to clear function results or not.

  • edits: optional array of BetaClearToolUses20250919Edit or BetaClearThinking20251015Edit or BetaCompact20260112Edit

    List of context management edits to apply

    • BetaClearToolUses20250919Edit object { type, clear_at_least, clear_tool_inputs, 3 more }

      • type: "clear_tool_uses_20250919"

        • "clear_tool_uses_20250919"

      • clear_at_least: optional BetaInputTokensClearAtLeast

        Minimum number of tokens that must be cleared when triggered. Context will only be modified if at least this many tokens can be removed.

        • type: "input_tokens"

          • "input_tokens"

        • value: number

      • clear_tool_inputs: optional boolean or array of string

        Whether to clear all tool inputs (bool) or specific tool inputs to clear (list)

        • boolean

        • array of string

      • exclude_tools: optional array of string

        Tool names whose uses are preserved from clearing

      • keep: optional BetaToolUsesKeep

        Number of tool uses to retain in the conversation

        • type: "tool_uses"

          • "tool_uses"

        • value: number

      • trigger: optional BetaInputTokensTrigger or BetaToolUsesTrigger

        Condition that triggers the context management strategy

        • BetaInputTokensTrigger object { type, value }

          • type: "input_tokens"

            • "input_tokens"

          • value: number

        • BetaToolUsesTrigger object { type, value }

          • type: "tool_uses"

            • "tool_uses"

          • value: number

    • BetaClearThinking20251015Edit object { type, keep }

      • type: "clear_thinking_20251015"

        • "clear_thinking_20251015"

      • keep: optional BetaThinkingTurns or BetaAllThinkingTurns or "all"

        Number of most recent assistant turns to keep thinking blocks for. Older turns will have their thinking blocks removed.

        • BetaThinkingTurns object { type, value }

          • type: "thinking_turns"

            • "thinking_turns"

          • value: number

        • BetaAllThinkingTurns object { type }

          • type: "all"

            • "all"

        • "all"

          • "all"

    • BetaCompact20260112Edit object { type, instructions, pause_after_compaction, trigger }

      Automatically compact older context when reaching the configured trigger threshold.

      • type: "compact_20260112"

        • "compact_20260112"

      • instructions: optional string

        Additional instructions for summarization.

      • pause_after_compaction: optional boolean

        Whether to pause after compaction and return the compaction block to the user.

      • trigger: optional BetaInputTokensTrigger

        When to trigger compaction. Defaults to 150000 input tokens.

• mcp_servers: optional array of BetaRequestMCPServerURLDefinition

  MCP servers to be utilized in this request

  • name: string

  • type: "url"

    • "url"

  • url: string

  • authorization_token: optional string

  • tool_configuration: optional BetaRequestMCPServerToolConfiguration

    • allowed_tools: optional array of string

    • enabled: optional boolean

• output_config: optional BetaOutputConfig

  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 BetaJSONOutputFormat

    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"

  • task_budget: optional BetaTokenTaskBudget

    User-configurable total token budget across contexts.

    • total: number

      Total token budget across all contexts in the session.

    • type: "tokens"

      The budget type. Currently only 'tokens' is supported.

      • "tokens"

    • remaining: optional number

      Remaining tokens in the budget. Use this to track usage across contexts when implementing compaction client-side. Defaults to total if not provided.

• output_format: optional BetaJSONOutputFormat

  Deprecated: Use output_config.format instead. See structured outputs

  A schema to specify Claude's output format in responses. This parameter will be removed in a future release.

• speed: optional "standard" or "fast"

  The inference speed mode for this request. "fast" enables high output-tokens-per-second inference.

  • "standard"

  • "fast"

• system: optional string or array of BetaTextBlockParam

  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.

  • string

  • array of BetaTextBlockParam

    • text: string

    • type: "text"

    • cache_control: optional BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • citations: optional array of BetaTextCitationParam

• thinking: optional BetaThinkingConfigParam

  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.

  • BetaThinkingConfigEnabled 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"

  • BetaThinkingConfigDisabled object { type }

    • type: "disabled"

      • "disabled"

  • BetaThinkingConfigAdaptive 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 BetaToolChoice

  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.

  • BetaToolChoiceAuto 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.

  • BetaToolChoiceAny 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.

  • BetaToolChoiceTool 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.

  • BetaToolChoiceNone object { type }

    The model will not be allowed to use tools.

    • type: "none"

      • "none"

• tools: optional array of BetaTool or BetaToolBash20241022 or BetaToolBash20250124 or 20 more

  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.

  • BetaTool 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 BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • 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"

  • BetaToolBash20241022 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_20241022"

      • "bash_20241022"

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

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

    • cache_control: optional BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • 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

  • BetaToolBash20250124 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 BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • 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

  • BetaCodeExecutionTool20250522 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 BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • 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

  • BetaCodeExecutionTool20250825 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 BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • 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

  • BetaCodeExecutionTool20260120 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 BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • 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

  • BetaToolComputerUse20241022 object { display_height_px, display_width_px, name, 7 more }

    • display_height_px: number

      The height of the display in pixels.

    • display_width_px: number

      The width of the display in pixels.

    • name: "computer"

      Name of the tool.

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

      • "computer"

    • type: "computer_20241022"

      • "computer_20241022"

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

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

    • cache_control: optional BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • 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.

    • display_number: optional number

      The X11 display number (e.g. 0, 1) for the display.

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaMemoryTool20250818 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 BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • 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

  • BetaToolComputerUse20250124 object { display_height_px, display_width_px, name, 7 more }

    • display_height_px: number

      The height of the display in pixels.

    • display_width_px: number

      The width of the display in pixels.

    • name: "computer"

      Name of the tool.

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

      • "computer"

    • type: "computer_20250124"

      • "computer_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 BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • 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.

    • display_number: optional number

      The X11 display number (e.g. 0, 1) for the display.

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaToolTextEditor20241022 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_20241022"

      • "text_editor_20241022"

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

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

    • cache_control: optional BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • 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

  • BetaToolComputerUse20251124 object { display_height_px, display_width_px, name, 8 more }

    • display_height_px: number

      The height of the display in pixels.

    • display_width_px: number

      The width of the display in pixels.

    • name: "computer"

      Name of the tool.

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

      • "computer"

    • type: "computer_20251124"

      • "computer_20251124"

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

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

    • cache_control: optional BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • 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.

    • display_number: optional number

      The X11 display number (e.g. 0, 1) for the display.

    • enable_zoom: optional boolean

      Whether to enable an action to take a zoomed-in screenshot of the screen.

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaToolTextEditor20250124 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 BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • 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

  • BetaToolTextEditor20250429 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 BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • 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

  • BetaToolTextEditor20250728 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 BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • 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

  • BetaWebSearchTool20250305 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 BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • 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 BetaUserLocation

      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.

  • BetaWebFetchTool20250910 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 BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • citations: optional BetaCitationsConfigParam

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

    • 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

  • BetaWebSearchTool20260209 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 BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • 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 BetaUserLocation

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

  • BetaWebFetchTool20260209 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 BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • citations: optional BetaCitationsConfigParam

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

    • 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

  • BetaWebFetchTool20260309 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 BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • citations: optional BetaCitationsConfigParam

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

    • 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.

  • BetaAdvisorTool20260301 object { model, name, type, 6 more }

    • model: Model

      The model that will complete your prompt.

      See models for additional details and options.

    • name: "advisor"

      Name of the tool.

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

      • "advisor"

    • type: "advisor_20260301"

      • "advisor_20260301"

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

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

    • cache_control: optional BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • caching: optional BetaCacheControlEphemeral

      Caching for the advisor's own prompt. When set, each advisor call writes a cache entry at the given TTL so subsequent calls in the same conversation read the stable prefix. When omitted, the advisor prompt is not cached.

    • 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

  • BetaToolSearchToolBm25_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 BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • 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

  • BetaToolSearchToolRegex20251119 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 BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • 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

  • BetaMCPToolset object { mcp_server_name, type, cache_control, 2 more }

    Configuration for a group of tools from an MCP server.

    Allows configuring enabled status and defer_loading for all tools from an MCP server, with optional per-tool overrides.

    • mcp_server_name: string

      Name of the MCP server to configure tools for

    • type: "mcp_toolset"

      • "mcp_toolset"

    • cache_control: optional BetaCacheControlEphemeral

      Create a cache control breakpoint at this content block.

    • configs: optional map[BetaMCPToolConfig]

      Configuration overrides for specific tools, keyed by tool name

      • defer_loading: optional boolean

      • enabled: optional boolean

    • default_config: optional BetaMCPToolDefaultConfig

      Default configuration applied to all tools from this server

      • defer_loading: optional boolean

      • enabled: optional boolean

Returns

• BetaMessageTokensCount object { context_management, input_tokens }

  • context_management: BetaCountTokensContextManagementResponse

    Information about context management applied to the message.

    • original_input_tokens: number

      The original token count before context management was applied

  • 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\",
          \"system\": [
            {
              \"text\": \"Today's date is 2024-06-01.\",
              \"type\": \"text\"
            }
          ],
          \"thinking\": {
            \"type\": \"adaptive\"
          },
          \"tools\": [
            {
              \"input_schema\": {
                \"type\": \"object\",
                \"properties\": {
                  \"location\": \"bar\",
                  \"unit\": \"bar\"
                },
                \"required\": [
                  \"location\"
                ]
              },
              \"name\": \"name\"
            }
          ]
        }"

Response

{
  "context_management": {
    "original_input_tokens": 0
  },
  "input_tokens": 2095
}