## Count tokens in a Message `client.Messages.CountTokens(ctx, body) (*MessageTokensCount, error)` **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](https://docs.claude.com/en/docs/build-with-claude/token-counting) ### Parameters - `body MessageCountTokensParams` - `Messages param.Field[[]MessageParamResp]` 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: ```json [{"role": "user", "content": "Hello, Claude"}] ``` Example with multiple conversational turns: ```json [ {"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: ```json [ {"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: ```json {"role": "user", "content": "Hello, Claude"} ``` ```json {"role": "user", "content": [{"type": "text", "text": "Hello, Claude"}]} ``` See [input examples](https://docs.claude.com/en/api/messages-examples). Note that if you want to include a [system prompt](https://docs.claude.com/en/docs/system-prompts), 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 []ContentBlockParamUnionResp` - `[]ContentBlockParamUnionResp` - `type TextBlockParamResp struct{…}` - `Text string` - `Type Text` - `const TextText Text = "text"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `Type Ephemeral` - `const EphemeralEphemeral Ephemeral = "ephemeral"` - `TTL CacheControlEphemeralTTL` 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`. - `const CacheControlEphemeralTTLTTL5m CacheControlEphemeralTTL = "5m"` - `const CacheControlEphemeralTTLTTL1h CacheControlEphemeralTTL = "1h"` - `Citations []TextCitationParamUnionResp` - `type CitationCharLocationParamResp struct{…}` - `CitedText string` - `DocumentIndex int64` - `DocumentTitle string` - `EndCharIndex int64` - `StartCharIndex int64` - `Type CharLocation` - `const CharLocationCharLocation CharLocation = "char_location"` - `type CitationPageLocationParamResp struct{…}` - `CitedText string` - `DocumentIndex int64` - `DocumentTitle string` - `EndPageNumber int64` - `StartPageNumber int64` - `Type PageLocation` - `const PageLocationPageLocation PageLocation = "page_location"` - `type CitationContentBlockLocationParamResp struct{…}` - `CitedText 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. - `DocumentIndex int64` - `DocumentTitle string` - `EndBlockIndex int64` 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`. - `StartBlockIndex int64` 0-based index of the first cited block in the source's `content` array. - `Type ContentBlockLocation` - `const ContentBlockLocationContentBlockLocation ContentBlockLocation = "content_block_location"` - `type CitationWebSearchResultLocationParamResp struct{…}` - `CitedText string` - `EncryptedIndex string` - `Title string` - `Type WebSearchResultLocation` - `const WebSearchResultLocationWebSearchResultLocation WebSearchResultLocation = "web_search_result_location"` - `URL string` - `type CitationSearchResultLocationParamResp struct{…}` - `CitedText 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. - `EndBlockIndex int64` 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`. - `SearchResultIndex int64` 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` - `StartBlockIndex int64` 0-based index of the first cited block in the source's `content` array. - `Title string` - `Type SearchResultLocation` - `const SearchResultLocationSearchResultLocation SearchResultLocation = "search_result_location"` - `type ImageBlockParamResp struct{…}` - `Source ImageBlockParamSourceUnionResp` - `type Base64ImageSource struct{…}` - `Data string` - `MediaType Base64ImageSourceMediaType` - `const Base64ImageSourceMediaTypeImageJPEG Base64ImageSourceMediaType = "image/jpeg"` - `const Base64ImageSourceMediaTypeImagePNG Base64ImageSourceMediaType = "image/png"` - `const Base64ImageSourceMediaTypeImageGIF Base64ImageSourceMediaType = "image/gif"` - `const Base64ImageSourceMediaTypeImageWebP Base64ImageSourceMediaType = "image/webp"` - `Type Base64` - `const Base64Base64 Base64 = "base64"` - `type URLImageSource struct{…}` - `Type URL` - `const URLURL URL = "url"` - `URL string` - `Type Image` - `const ImageImage Image = "image"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `type DocumentBlockParamResp struct{…}` - `Source DocumentBlockParamSourceUnionResp` - `type Base64PDFSource struct{…}` - `Data string` - `MediaType ApplicationPDF` - `const ApplicationPDFApplicationPDF ApplicationPDF = "application/pdf"` - `Type Base64` - `const Base64Base64 Base64 = "base64"` - `type PlainTextSource struct{…}` - `Data string` - `MediaType TextPlain` - `const TextPlainTextPlain TextPlain = "text/plain"` - `Type Text` - `const TextText Text = "text"` - `type ContentBlockSource struct{…}` - `Content ContentBlockSourceContentUnion` - `string` - `[]ContentBlockSourceContentItemUnion` - `type TextBlockParamResp struct{…}` - `type ImageBlockParamResp struct{…}` - `Type Content` - `const ContentContent Content = "content"` - `type URLPDFSource struct{…}` - `Type URL` - `const URLURL URL = "url"` - `URL string` - `Type Document` - `const DocumentDocument Document = "document"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `Citations CitationsConfigParamResp` - `Enabled bool` - `Context string` - `Title string` - `type SearchResultBlockParamResp struct{…}` - `Content []TextBlockParamResp` - `Text string` - `Type Text` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `Citations []TextCitationParamUnionResp` - `Source string` - `Title string` - `Type SearchResult` - `const SearchResultSearchResult SearchResult = "search_result"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `Citations CitationsConfigParamResp` - `type ThinkingBlockParamResp struct{…}` - `Signature string` - `Thinking string` - `Type Thinking` - `const ThinkingThinking Thinking = "thinking"` - `type RedactedThinkingBlockParamResp struct{…}` - `Data string` - `Type RedactedThinking` - `const RedactedThinkingRedactedThinking RedactedThinking = "redacted_thinking"` - `type ToolUseBlockParamResp struct{…}` - `ID string` - `Input map[string, any]` - `Name string` - `Type ToolUse` - `const ToolUseToolUse ToolUse = "tool_use"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `Caller ToolUseBlockParamCallerUnionResp` Tool invocation directly from the model. - `type DirectCaller struct{…}` Tool invocation directly from the model. - `Type Direct` - `const DirectDirect Direct = "direct"` - `type ServerToolCaller struct{…}` Tool invocation generated by a server-side tool. - `ToolID string` - `Type CodeExecution20250825` - `const CodeExecution20250825CodeExecution20250825 CodeExecution20250825 = "code_execution_20250825"` - `type ServerToolCaller20260120 struct{…}` - `ToolID string` - `Type CodeExecution20260120` - `const CodeExecution20260120CodeExecution20260120 CodeExecution20260120 = "code_execution_20260120"` - `type ToolResultBlockParamResp struct{…}` - `ToolUseID string` - `Type ToolResult` - `const ToolResultToolResult ToolResult = "tool_result"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `Content []ToolResultBlockParamContentUnionResp` - `[]ToolResultBlockParamContentUnionResp` - `type TextBlockParamResp struct{…}` - `type ImageBlockParamResp struct{…}` - `type SearchResultBlockParamResp struct{…}` - `type DocumentBlockParamResp struct{…}` - `type ToolReferenceBlockParamResp struct{…}` Tool reference block that can be included in tool_result content. - `ToolName string` - `Type ToolReference` - `const ToolReferenceToolReference ToolReference = "tool_reference"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `IsError bool` - `type ServerToolUseBlockParamResp struct{…}` - `ID string` - `Input map[string, any]` - `Name ServerToolUseBlockParamName` - `const ServerToolUseBlockParamNameWebSearch ServerToolUseBlockParamName = "web_search"` - `const ServerToolUseBlockParamNameWebFetch ServerToolUseBlockParamName = "web_fetch"` - `const ServerToolUseBlockParamNameCodeExecution ServerToolUseBlockParamName = "code_execution"` - `const ServerToolUseBlockParamNameBashCodeExecution ServerToolUseBlockParamName = "bash_code_execution"` - `const ServerToolUseBlockParamNameTextEditorCodeExecution ServerToolUseBlockParamName = "text_editor_code_execution"` - `const ServerToolUseBlockParamNameToolSearchToolRegex ServerToolUseBlockParamName = "tool_search_tool_regex"` - `const ServerToolUseBlockParamNameToolSearchToolBm25 ServerToolUseBlockParamName = "tool_search_tool_bm25"` - `Type ServerToolUse` - `const ServerToolUseServerToolUse ServerToolUse = "server_tool_use"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `Caller ServerToolUseBlockParamCallerUnionResp` Tool invocation directly from the model. - `type DirectCaller struct{…}` Tool invocation directly from the model. - `type ServerToolCaller struct{…}` Tool invocation generated by a server-side tool. - `type ServerToolCaller20260120 struct{…}` - `type WebSearchToolResultBlockParamResp struct{…}` - `Content WebSearchToolResultBlockParamContentUnionResp` - `[]WebSearchResultBlockParamResp` - `EncryptedContent string` - `Title string` - `Type WebSearchResult` - `const WebSearchResultWebSearchResult WebSearchResult = "web_search_result"` - `URL string` - `PageAge string` - `type WebSearchToolRequestError struct{…}` - `ErrorCode WebSearchToolResultErrorCode` - `const WebSearchToolResultErrorCodeInvalidToolInput WebSearchToolResultErrorCode = "invalid_tool_input"` - `const WebSearchToolResultErrorCodeUnavailable WebSearchToolResultErrorCode = "unavailable"` - `const WebSearchToolResultErrorCodeMaxUsesExceeded WebSearchToolResultErrorCode = "max_uses_exceeded"` - `const WebSearchToolResultErrorCodeTooManyRequests WebSearchToolResultErrorCode = "too_many_requests"` - `const WebSearchToolResultErrorCodeQueryTooLong WebSearchToolResultErrorCode = "query_too_long"` - `const WebSearchToolResultErrorCodeRequestTooLarge WebSearchToolResultErrorCode = "request_too_large"` - `Type WebSearchToolResultError` - `const WebSearchToolResultErrorWebSearchToolResultError WebSearchToolResultError = "web_search_tool_result_error"` - `ToolUseID string` - `Type WebSearchToolResult` - `const WebSearchToolResultWebSearchToolResult WebSearchToolResult = "web_search_tool_result"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `Caller WebSearchToolResultBlockParamCallerUnionResp` Tool invocation directly from the model. - `type DirectCaller struct{…}` Tool invocation directly from the model. - `type ServerToolCaller struct{…}` Tool invocation generated by a server-side tool. - `type ServerToolCaller20260120 struct{…}` - `type WebFetchToolResultBlockParamResp struct{…}` - `Content WebFetchToolResultBlockParamContentUnionResp` - `type WebFetchToolResultErrorBlockParamResp struct{…}` - `ErrorCode WebFetchToolResultErrorCode` - `const WebFetchToolResultErrorCodeInvalidToolInput WebFetchToolResultErrorCode = "invalid_tool_input"` - `const WebFetchToolResultErrorCodeURLTooLong WebFetchToolResultErrorCode = "url_too_long"` - `const WebFetchToolResultErrorCodeURLNotAllowed WebFetchToolResultErrorCode = "url_not_allowed"` - `const WebFetchToolResultErrorCodeURLNotInPriorContext WebFetchToolResultErrorCode = "url_not_in_prior_context"` - `const WebFetchToolResultErrorCodeURLNotAccessible WebFetchToolResultErrorCode = "url_not_accessible"` - `const WebFetchToolResultErrorCodeUnsupportedContentType WebFetchToolResultErrorCode = "unsupported_content_type"` - `const WebFetchToolResultErrorCodeTooManyRequests WebFetchToolResultErrorCode = "too_many_requests"` - `const WebFetchToolResultErrorCodeMaxUsesExceeded WebFetchToolResultErrorCode = "max_uses_exceeded"` - `const WebFetchToolResultErrorCodeUnavailable WebFetchToolResultErrorCode = "unavailable"` - `Type WebFetchToolResultError` - `const WebFetchToolResultErrorWebFetchToolResultError WebFetchToolResultError = "web_fetch_tool_result_error"` - `type WebFetchBlockParamResp struct{…}` - `Content DocumentBlockParamResp` - `Type WebFetchResult` - `const WebFetchResultWebFetchResult WebFetchResult = "web_fetch_result"` - `URL string` Fetched content URL - `RetrievedAt string` ISO 8601 timestamp when the content was retrieved - `ToolUseID string` - `Type WebFetchToolResult` - `const WebFetchToolResultWebFetchToolResult WebFetchToolResult = "web_fetch_tool_result"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `Caller WebFetchToolResultBlockParamCallerUnionResp` Tool invocation directly from the model. - `type DirectCaller struct{…}` Tool invocation directly from the model. - `type ServerToolCaller struct{…}` Tool invocation generated by a server-side tool. - `type ServerToolCaller20260120 struct{…}` - `type CodeExecutionToolResultBlockParamResp struct{…}` - `Content CodeExecutionToolResultBlockParamContentUnionResp` Code execution result with encrypted stdout for PFC + web_search results. - `type CodeExecutionToolResultErrorParamResp struct{…}` - `ErrorCode CodeExecutionToolResultErrorCode` - `const CodeExecutionToolResultErrorCodeInvalidToolInput CodeExecutionToolResultErrorCode = "invalid_tool_input"` - `const CodeExecutionToolResultErrorCodeUnavailable CodeExecutionToolResultErrorCode = "unavailable"` - `const CodeExecutionToolResultErrorCodeTooManyRequests CodeExecutionToolResultErrorCode = "too_many_requests"` - `const CodeExecutionToolResultErrorCodeExecutionTimeExceeded CodeExecutionToolResultErrorCode = "execution_time_exceeded"` - `Type CodeExecutionToolResultError` - `const CodeExecutionToolResultErrorCodeExecutionToolResultError CodeExecutionToolResultError = "code_execution_tool_result_error"` - `type CodeExecutionResultBlockParamResp struct{…}` - `Content []CodeExecutionOutputBlockParamResp` - `FileID string` - `Type CodeExecutionOutput` - `const CodeExecutionOutputCodeExecutionOutput CodeExecutionOutput = "code_execution_output"` - `ReturnCode int64` - `Stderr string` - `Stdout string` - `Type CodeExecutionResult` - `const CodeExecutionResultCodeExecutionResult CodeExecutionResult = "code_execution_result"` - `type EncryptedCodeExecutionResultBlockParamResp struct{…}` Code execution result with encrypted stdout for PFC + web_search results. - `Content []CodeExecutionOutputBlockParamResp` - `FileID string` - `Type CodeExecutionOutput` - `EncryptedStdout string` - `ReturnCode int64` - `Stderr string` - `Type EncryptedCodeExecutionResult` - `const EncryptedCodeExecutionResultEncryptedCodeExecutionResult EncryptedCodeExecutionResult = "encrypted_code_execution_result"` - `ToolUseID string` - `Type CodeExecutionToolResult` - `const CodeExecutionToolResultCodeExecutionToolResult CodeExecutionToolResult = "code_execution_tool_result"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `type BashCodeExecutionToolResultBlockParamResp struct{…}` - `Content BashCodeExecutionToolResultBlockParamContentUnionResp` - `type BashCodeExecutionToolResultErrorParamResp struct{…}` - `ErrorCode BashCodeExecutionToolResultErrorCode` - `const BashCodeExecutionToolResultErrorCodeInvalidToolInput BashCodeExecutionToolResultErrorCode = "invalid_tool_input"` - `const BashCodeExecutionToolResultErrorCodeUnavailable BashCodeExecutionToolResultErrorCode = "unavailable"` - `const BashCodeExecutionToolResultErrorCodeTooManyRequests BashCodeExecutionToolResultErrorCode = "too_many_requests"` - `const BashCodeExecutionToolResultErrorCodeExecutionTimeExceeded BashCodeExecutionToolResultErrorCode = "execution_time_exceeded"` - `const BashCodeExecutionToolResultErrorCodeOutputFileTooLarge BashCodeExecutionToolResultErrorCode = "output_file_too_large"` - `Type BashCodeExecutionToolResultError` - `const BashCodeExecutionToolResultErrorBashCodeExecutionToolResultError BashCodeExecutionToolResultError = "bash_code_execution_tool_result_error"` - `type BashCodeExecutionResultBlockParamResp struct{…}` - `Content []BashCodeExecutionOutputBlockParamResp` - `FileID string` - `Type BashCodeExecutionOutput` - `const BashCodeExecutionOutputBashCodeExecutionOutput BashCodeExecutionOutput = "bash_code_execution_output"` - `ReturnCode int64` - `Stderr string` - `Stdout string` - `Type BashCodeExecutionResult` - `const BashCodeExecutionResultBashCodeExecutionResult BashCodeExecutionResult = "bash_code_execution_result"` - `ToolUseID string` - `Type BashCodeExecutionToolResult` - `const BashCodeExecutionToolResultBashCodeExecutionToolResult BashCodeExecutionToolResult = "bash_code_execution_tool_result"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `type TextEditorCodeExecutionToolResultBlockParamResp struct{…}` - `Content TextEditorCodeExecutionToolResultBlockParamContentUnionResp` - `type TextEditorCodeExecutionToolResultErrorParamResp struct{…}` - `ErrorCode TextEditorCodeExecutionToolResultErrorCode` - `const TextEditorCodeExecutionToolResultErrorCodeInvalidToolInput TextEditorCodeExecutionToolResultErrorCode = "invalid_tool_input"` - `const TextEditorCodeExecutionToolResultErrorCodeUnavailable TextEditorCodeExecutionToolResultErrorCode = "unavailable"` - `const TextEditorCodeExecutionToolResultErrorCodeTooManyRequests TextEditorCodeExecutionToolResultErrorCode = "too_many_requests"` - `const TextEditorCodeExecutionToolResultErrorCodeExecutionTimeExceeded TextEditorCodeExecutionToolResultErrorCode = "execution_time_exceeded"` - `const TextEditorCodeExecutionToolResultErrorCodeFileNotFound TextEditorCodeExecutionToolResultErrorCode = "file_not_found"` - `Type TextEditorCodeExecutionToolResultError` - `const TextEditorCodeExecutionToolResultErrorTextEditorCodeExecutionToolResultError TextEditorCodeExecutionToolResultError = "text_editor_code_execution_tool_result_error"` - `ErrorMessage string` - `type TextEditorCodeExecutionViewResultBlockParamResp struct{…}` - `Content string` - `FileType TextEditorCodeExecutionViewResultBlockParamFileType` - `const TextEditorCodeExecutionViewResultBlockParamFileTypeText TextEditorCodeExecutionViewResultBlockParamFileType = "text"` - `const TextEditorCodeExecutionViewResultBlockParamFileTypeImage TextEditorCodeExecutionViewResultBlockParamFileType = "image"` - `const TextEditorCodeExecutionViewResultBlockParamFileTypePDF TextEditorCodeExecutionViewResultBlockParamFileType = "pdf"` - `Type TextEditorCodeExecutionViewResult` - `const TextEditorCodeExecutionViewResultTextEditorCodeExecutionViewResult TextEditorCodeExecutionViewResult = "text_editor_code_execution_view_result"` - `NumLines int64` - `StartLine int64` - `TotalLines int64` - `type TextEditorCodeExecutionCreateResultBlockParamResp struct{…}` - `IsFileUpdate bool` - `Type TextEditorCodeExecutionCreateResult` - `const TextEditorCodeExecutionCreateResultTextEditorCodeExecutionCreateResult TextEditorCodeExecutionCreateResult = "text_editor_code_execution_create_result"` - `type TextEditorCodeExecutionStrReplaceResultBlockParamResp struct{…}` - `Type TextEditorCodeExecutionStrReplaceResult` - `const TextEditorCodeExecutionStrReplaceResultTextEditorCodeExecutionStrReplaceResult TextEditorCodeExecutionStrReplaceResult = "text_editor_code_execution_str_replace_result"` - `Lines []string` - `NewLines int64` - `NewStart int64` - `OldLines int64` - `OldStart int64` - `ToolUseID string` - `Type TextEditorCodeExecutionToolResult` - `const TextEditorCodeExecutionToolResultTextEditorCodeExecutionToolResult TextEditorCodeExecutionToolResult = "text_editor_code_execution_tool_result"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `type ToolSearchToolResultBlockParamResp struct{…}` - `Content ToolSearchToolResultBlockParamContentUnionResp` - `type ToolSearchToolResultErrorParamResp struct{…}` - `ErrorCode ToolSearchToolResultErrorCode` - `const ToolSearchToolResultErrorCodeInvalidToolInput ToolSearchToolResultErrorCode = "invalid_tool_input"` - `const ToolSearchToolResultErrorCodeUnavailable ToolSearchToolResultErrorCode = "unavailable"` - `const ToolSearchToolResultErrorCodeTooManyRequests ToolSearchToolResultErrorCode = "too_many_requests"` - `const ToolSearchToolResultErrorCodeExecutionTimeExceeded ToolSearchToolResultErrorCode = "execution_time_exceeded"` - `Type ToolSearchToolResultError` - `const ToolSearchToolResultErrorToolSearchToolResultError ToolSearchToolResultError = "tool_search_tool_result_error"` - `type ToolSearchToolSearchResultBlockParamResp struct{…}` - `ToolReferences []ToolReferenceBlockParamResp` - `ToolName string` - `Type ToolReference` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `Type ToolSearchToolSearchResult` - `const ToolSearchToolSearchResultToolSearchToolSearchResult ToolSearchToolSearchResult = "tool_search_tool_search_result"` - `ToolUseID string` - `Type ToolSearchToolResult` - `const ToolSearchToolResultToolSearchToolResult ToolSearchToolResult = "tool_search_tool_result"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `type ContainerUploadBlockParamResp struct{…}` 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. - `FileID string` - `Type ContainerUpload` - `const ContainerUploadContainerUpload ContainerUpload = "container_upload"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `type MidConversationSystemBlockParamResp struct{…}` System instructions that appear mid-conversation. Use this block to provide or update system-level instructions at a specific point in the conversation, rather than only via the top-level `system` parameter. - `Content []TextBlockParamResp` System instruction text blocks. - `Text string` - `Type Text` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `Citations []TextCitationParamUnionResp` - `Type MidConvSystem` - `const MidConvSystemMidConvSystem MidConvSystem = "mid_conv_system"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `Role MessageParamRole` - `const MessageParamRoleUser MessageParamRole = "user"` - `const MessageParamRoleAssistant MessageParamRole = "assistant"` - `const MessageParamRoleSystem MessageParamRole = "system"` - `Model param.Field[Model]` The model that will complete your prompt. See [models](https://docs.anthropic.com/en/docs/models-overview) for additional details and options. - `CacheControl param.Field[CacheControlEphemeral]` Top-level cache control automatically applies a cache_control marker to the last cacheable block in the request. - `OutputConfig param.Field[OutputConfig]` Configuration options for the model's output, such as the output format. - `System param.Field[MessageCountTokensParamsSystemUnion]` 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](https://docs.claude.com/en/docs/system-prompts). - `string` - `type MessageCountTokensParamsSystemArray []TextBlockParamResp` - `Text string` - `Type Text` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `Citations []TextCitationParamUnionResp` - `Thinking param.Field[ThinkingConfigParamUnionResp]` 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](https://docs.claude.com/en/docs/build-with-claude/extended-thinking) for details. - `ToolChoice param.Field[ToolChoiceUnion]` 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. - `Tools param.Field[[]MessageCountTokensToolUnion]` 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](https://docs.claude.com/en/docs/agents-and-tools/tool-use/overview#server-tools), see their individual documentation as each has its own behavior (e.g., the [web search tool](https://docs.claude.com/en/docs/agents-and-tools/tool-use/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](https://json-schema.org/draft/2020-12) for the tool `input` shape that the model will produce in `tool_use` output content blocks. For example, if you defined `tools` as: ```json [ { "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: ```json [ { "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: ```json [ { "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](https://docs.claude.com/en/docs/tool-use) for more details. - `type Tool struct{…}` - `InputSchema ToolInputSchema` [JSON schema](https://json-schema.org/draft/2020-12) for this tool's input. This defines the shape of the `input` that your tool accepts and that the model will produce. - `Type Object` - `const ObjectObject Object = "object"` - `Properties map[string, any]` - `Required []string` - `Name string` Name of the tool. This is how the tool will be called by the model and in `tool_use` blocks. - `AllowedCallers []string` - `const ToolAllowedCallerDirect ToolAllowedCaller = "direct"` - `const ToolAllowedCallerCodeExecution20250825 ToolAllowedCaller = "code_execution_20250825"` - `const ToolAllowedCallerCodeExecution20260120 ToolAllowedCaller = "code_execution_20260120"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `DeferLoading bool` If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search. - `Description 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. - `EagerInputStreaming bool` 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. - `InputExamples []map[string, any]` - `Strict bool` When true, guarantees schema validation on tool names and inputs - `Type ToolType` - `const ToolTypeCustom ToolType = "custom"` - `type ToolBash20250124 struct{…}` - `Name Bash` Name of the tool. This is how the tool will be called by the model and in `tool_use` blocks. - `const BashBash Bash = "bash"` - `Type Bash20250124` - `const Bash20250124Bash20250124 Bash20250124 = "bash_20250124"` - `AllowedCallers []string` - `const ToolBash20250124AllowedCallerDirect ToolBash20250124AllowedCaller = "direct"` - `const ToolBash20250124AllowedCallerCodeExecution20250825 ToolBash20250124AllowedCaller = "code_execution_20250825"` - `const ToolBash20250124AllowedCallerCodeExecution20260120 ToolBash20250124AllowedCaller = "code_execution_20260120"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `DeferLoading bool` If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search. - `InputExamples []map[string, any]` - `Strict bool` When true, guarantees schema validation on tool names and inputs - `type CodeExecutionTool20250522 struct{…}` - `Name CodeExecution` Name of the tool. This is how the tool will be called by the model and in `tool_use` blocks. - `const CodeExecutionCodeExecution CodeExecution = "code_execution"` - `Type CodeExecution20250522` - `const CodeExecution20250522CodeExecution20250522 CodeExecution20250522 = "code_execution_20250522"` - `AllowedCallers []string` - `const CodeExecutionTool20250522AllowedCallerDirect CodeExecutionTool20250522AllowedCaller = "direct"` - `const CodeExecutionTool20250522AllowedCallerCodeExecution20250825 CodeExecutionTool20250522AllowedCaller = "code_execution_20250825"` - `const CodeExecutionTool20250522AllowedCallerCodeExecution20260120 CodeExecutionTool20250522AllowedCaller = "code_execution_20260120"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `DeferLoading bool` If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search. - `Strict bool` When true, guarantees schema validation on tool names and inputs - `type CodeExecutionTool20250825 struct{…}` - `Name CodeExecution` Name of the tool. This is how the tool will be called by the model and in `tool_use` blocks. - `const CodeExecutionCodeExecution CodeExecution = "code_execution"` - `Type CodeExecution20250825` - `const CodeExecution20250825CodeExecution20250825 CodeExecution20250825 = "code_execution_20250825"` - `AllowedCallers []string` - `const CodeExecutionTool20250825AllowedCallerDirect CodeExecutionTool20250825AllowedCaller = "direct"` - `const CodeExecutionTool20250825AllowedCallerCodeExecution20250825 CodeExecutionTool20250825AllowedCaller = "code_execution_20250825"` - `const CodeExecutionTool20250825AllowedCallerCodeExecution20260120 CodeExecutionTool20250825AllowedCaller = "code_execution_20260120"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `DeferLoading bool` If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search. - `Strict bool` When true, guarantees schema validation on tool names and inputs - `type CodeExecutionTool20260120 struct{…}` Code execution tool with REPL state persistence (daemon mode + gVisor checkpoint). - `Name CodeExecution` Name of the tool. This is how the tool will be called by the model and in `tool_use` blocks. - `const CodeExecutionCodeExecution CodeExecution = "code_execution"` - `Type CodeExecution20260120` - `const CodeExecution20260120CodeExecution20260120 CodeExecution20260120 = "code_execution_20260120"` - `AllowedCallers []string` - `const CodeExecutionTool20260120AllowedCallerDirect CodeExecutionTool20260120AllowedCaller = "direct"` - `const CodeExecutionTool20260120AllowedCallerCodeExecution20250825 CodeExecutionTool20260120AllowedCaller = "code_execution_20250825"` - `const CodeExecutionTool20260120AllowedCallerCodeExecution20260120 CodeExecutionTool20260120AllowedCaller = "code_execution_20260120"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `DeferLoading bool` If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search. - `Strict bool` When true, guarantees schema validation on tool names and inputs - `type MemoryTool20250818 struct{…}` - `Name Memory` Name of the tool. This is how the tool will be called by the model and in `tool_use` blocks. - `const MemoryMemory Memory = "memory"` - `Type Memory20250818` - `const Memory20250818Memory20250818 Memory20250818 = "memory_20250818"` - `AllowedCallers []string` - `const MemoryTool20250818AllowedCallerDirect MemoryTool20250818AllowedCaller = "direct"` - `const MemoryTool20250818AllowedCallerCodeExecution20250825 MemoryTool20250818AllowedCaller = "code_execution_20250825"` - `const MemoryTool20250818AllowedCallerCodeExecution20260120 MemoryTool20250818AllowedCaller = "code_execution_20260120"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `DeferLoading bool` If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search. - `InputExamples []map[string, any]` - `Strict bool` When true, guarantees schema validation on tool names and inputs - `type ToolTextEditor20250124 struct{…}` - `Name StrReplaceEditor` Name of the tool. This is how the tool will be called by the model and in `tool_use` blocks. - `const StrReplaceEditorStrReplaceEditor StrReplaceEditor = "str_replace_editor"` - `Type TextEditor20250124` - `const TextEditor20250124TextEditor20250124 TextEditor20250124 = "text_editor_20250124"` - `AllowedCallers []string` - `const ToolTextEditor20250124AllowedCallerDirect ToolTextEditor20250124AllowedCaller = "direct"` - `const ToolTextEditor20250124AllowedCallerCodeExecution20250825 ToolTextEditor20250124AllowedCaller = "code_execution_20250825"` - `const ToolTextEditor20250124AllowedCallerCodeExecution20260120 ToolTextEditor20250124AllowedCaller = "code_execution_20260120"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `DeferLoading bool` If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search. - `InputExamples []map[string, any]` - `Strict bool` When true, guarantees schema validation on tool names and inputs - `type ToolTextEditor20250429 struct{…}` - `Name StrReplaceBasedEditTool` Name of the tool. This is how the tool will be called by the model and in `tool_use` blocks. - `const StrReplaceBasedEditToolStrReplaceBasedEditTool StrReplaceBasedEditTool = "str_replace_based_edit_tool"` - `Type TextEditor20250429` - `const TextEditor20250429TextEditor20250429 TextEditor20250429 = "text_editor_20250429"` - `AllowedCallers []string` - `const ToolTextEditor20250429AllowedCallerDirect ToolTextEditor20250429AllowedCaller = "direct"` - `const ToolTextEditor20250429AllowedCallerCodeExecution20250825 ToolTextEditor20250429AllowedCaller = "code_execution_20250825"` - `const ToolTextEditor20250429AllowedCallerCodeExecution20260120 ToolTextEditor20250429AllowedCaller = "code_execution_20260120"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `DeferLoading bool` If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search. - `InputExamples []map[string, any]` - `Strict bool` When true, guarantees schema validation on tool names and inputs - `type ToolTextEditor20250728 struct{…}` - `Name StrReplaceBasedEditTool` Name of the tool. This is how the tool will be called by the model and in `tool_use` blocks. - `const StrReplaceBasedEditToolStrReplaceBasedEditTool StrReplaceBasedEditTool = "str_replace_based_edit_tool"` - `Type TextEditor20250728` - `const TextEditor20250728TextEditor20250728 TextEditor20250728 = "text_editor_20250728"` - `AllowedCallers []string` - `const ToolTextEditor20250728AllowedCallerDirect ToolTextEditor20250728AllowedCaller = "direct"` - `const ToolTextEditor20250728AllowedCallerCodeExecution20250825 ToolTextEditor20250728AllowedCaller = "code_execution_20250825"` - `const ToolTextEditor20250728AllowedCallerCodeExecution20260120 ToolTextEditor20250728AllowedCaller = "code_execution_20260120"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `DeferLoading bool` If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search. - `InputExamples []map[string, any]` - `MaxCharacters int64` Maximum number of characters to display when viewing a file. If not specified, defaults to displaying the full file. - `Strict bool` When true, guarantees schema validation on tool names and inputs - `type WebSearchTool20250305 struct{…}` - `Name WebSearch` Name of the tool. This is how the tool will be called by the model and in `tool_use` blocks. - `const WebSearchWebSearch WebSearch = "web_search"` - `Type WebSearch20250305` - `const WebSearch20250305WebSearch20250305 WebSearch20250305 = "web_search_20250305"` - `AllowedCallers []string` - `const WebSearchTool20250305AllowedCallerDirect WebSearchTool20250305AllowedCaller = "direct"` - `const WebSearchTool20250305AllowedCallerCodeExecution20250825 WebSearchTool20250305AllowedCaller = "code_execution_20250825"` - `const WebSearchTool20250305AllowedCallerCodeExecution20260120 WebSearchTool20250305AllowedCaller = "code_execution_20260120"` - `AllowedDomains []string` If provided, only these domains will be included in results. Cannot be used alongside `blocked_domains`. - `BlockedDomains []string` If provided, these domains will never appear in results. Cannot be used alongside `allowed_domains`. - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `DeferLoading bool` If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search. - `MaxUses int64` Maximum number of times the tool can be used in the API request. - `Strict bool` When true, guarantees schema validation on tool names and inputs - `UserLocation UserLocation` Parameters for the user's location. Used to provide more relevant search results. - `Type Approximate` - `const ApproximateApproximate Approximate = "approximate"` - `City string` The city of the user. - `Country string` The two letter [ISO country code](https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2) of the user. - `Region string` The region of the user. - `Timezone string` The [IANA timezone](https://nodatime.org/TimeZones) of the user. - `type WebFetchTool20250910 struct{…}` - `Name WebFetch` Name of the tool. This is how the tool will be called by the model and in `tool_use` blocks. - `const WebFetchWebFetch WebFetch = "web_fetch"` - `Type WebFetch20250910` - `const WebFetch20250910WebFetch20250910 WebFetch20250910 = "web_fetch_20250910"` - `AllowedCallers []string` - `const WebFetchTool20250910AllowedCallerDirect WebFetchTool20250910AllowedCaller = "direct"` - `const WebFetchTool20250910AllowedCallerCodeExecution20250825 WebFetchTool20250910AllowedCaller = "code_execution_20250825"` - `const WebFetchTool20250910AllowedCallerCodeExecution20260120 WebFetchTool20250910AllowedCaller = "code_execution_20260120"` - `AllowedDomains []string` List of domains to allow fetching from - `BlockedDomains []string` List of domains to block fetching from - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `Citations CitationsConfigParamResp` Citations configuration for fetched documents. Citations are disabled by default. - `DeferLoading bool` If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search. - `MaxContentTokens int64` 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. - `MaxUses int64` Maximum number of times the tool can be used in the API request. - `Strict bool` When true, guarantees schema validation on tool names and inputs - `type WebSearchTool20260209 struct{…}` - `Name WebSearch` Name of the tool. This is how the tool will be called by the model and in `tool_use` blocks. - `const WebSearchWebSearch WebSearch = "web_search"` - `Type WebSearch20260209` - `const WebSearch20260209WebSearch20260209 WebSearch20260209 = "web_search_20260209"` - `AllowedCallers []string` - `const WebSearchTool20260209AllowedCallerDirect WebSearchTool20260209AllowedCaller = "direct"` - `const WebSearchTool20260209AllowedCallerCodeExecution20250825 WebSearchTool20260209AllowedCaller = "code_execution_20250825"` - `const WebSearchTool20260209AllowedCallerCodeExecution20260120 WebSearchTool20260209AllowedCaller = "code_execution_20260120"` - `AllowedDomains []string` If provided, only these domains will be included in results. Cannot be used alongside `blocked_domains`. - `BlockedDomains []string` If provided, these domains will never appear in results. Cannot be used alongside `allowed_domains`. - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `DeferLoading bool` If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search. - `MaxUses int64` Maximum number of times the tool can be used in the API request. - `Strict bool` When true, guarantees schema validation on tool names and inputs - `UserLocation UserLocation` Parameters for the user's location. Used to provide more relevant search results. - `type WebFetchTool20260209 struct{…}` - `Name WebFetch` Name of the tool. This is how the tool will be called by the model and in `tool_use` blocks. - `const WebFetchWebFetch WebFetch = "web_fetch"` - `Type WebFetch20260209` - `const WebFetch20260209WebFetch20260209 WebFetch20260209 = "web_fetch_20260209"` - `AllowedCallers []string` - `const WebFetchTool20260209AllowedCallerDirect WebFetchTool20260209AllowedCaller = "direct"` - `const WebFetchTool20260209AllowedCallerCodeExecution20250825 WebFetchTool20260209AllowedCaller = "code_execution_20250825"` - `const WebFetchTool20260209AllowedCallerCodeExecution20260120 WebFetchTool20260209AllowedCaller = "code_execution_20260120"` - `AllowedDomains []string` List of domains to allow fetching from - `BlockedDomains []string` List of domains to block fetching from - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `Citations CitationsConfigParamResp` Citations configuration for fetched documents. Citations are disabled by default. - `DeferLoading bool` If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search. - `MaxContentTokens int64` 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. - `MaxUses int64` Maximum number of times the tool can be used in the API request. - `Strict bool` When true, guarantees schema validation on tool names and inputs - `type WebFetchTool20260309 struct{…}` Web fetch tool with use_cache parameter for bypassing cached content. - `Name WebFetch` Name of the tool. This is how the tool will be called by the model and in `tool_use` blocks. - `const WebFetchWebFetch WebFetch = "web_fetch"` - `Type WebFetch20260309` - `const WebFetch20260309WebFetch20260309 WebFetch20260309 = "web_fetch_20260309"` - `AllowedCallers []string` - `const WebFetchTool20260309AllowedCallerDirect WebFetchTool20260309AllowedCaller = "direct"` - `const WebFetchTool20260309AllowedCallerCodeExecution20250825 WebFetchTool20260309AllowedCaller = "code_execution_20250825"` - `const WebFetchTool20260309AllowedCallerCodeExecution20260120 WebFetchTool20260309AllowedCaller = "code_execution_20260120"` - `AllowedDomains []string` List of domains to allow fetching from - `BlockedDomains []string` List of domains to block fetching from - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `Citations CitationsConfigParamResp` Citations configuration for fetched documents. Citations are disabled by default. - `DeferLoading bool` If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search. - `MaxContentTokens int64` 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. - `MaxUses int64` Maximum number of times the tool can be used in the API request. - `Strict bool` When true, guarantees schema validation on tool names and inputs - `UseCache bool` 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. - `type ToolSearchToolBm25_20251119 struct{…}` - `Name ToolSearchToolBm25` Name of the tool. This is how the tool will be called by the model and in `tool_use` blocks. - `const ToolSearchToolBm25ToolSearchToolBm25 ToolSearchToolBm25 = "tool_search_tool_bm25"` - `Type ToolSearchToolBm25_20251119Type` - `const ToolSearchToolBm25_20251119TypeToolSearchToolBm25_20251119 ToolSearchToolBm25_20251119Type = "tool_search_tool_bm25_20251119"` - `const ToolSearchToolBm25_20251119TypeToolSearchToolBm25 ToolSearchToolBm25_20251119Type = "tool_search_tool_bm25"` - `AllowedCallers []string` - `const ToolSearchToolBm25_20251119AllowedCallerDirect ToolSearchToolBm25_20251119AllowedCaller = "direct"` - `const ToolSearchToolBm25_20251119AllowedCallerCodeExecution20250825 ToolSearchToolBm25_20251119AllowedCaller = "code_execution_20250825"` - `const ToolSearchToolBm25_20251119AllowedCallerCodeExecution20260120 ToolSearchToolBm25_20251119AllowedCaller = "code_execution_20260120"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `DeferLoading bool` If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search. - `Strict bool` When true, guarantees schema validation on tool names and inputs - `type ToolSearchToolRegex20251119 struct{…}` - `Name ToolSearchToolRegex` Name of the tool. This is how the tool will be called by the model and in `tool_use` blocks. - `const ToolSearchToolRegexToolSearchToolRegex ToolSearchToolRegex = "tool_search_tool_regex"` - `Type ToolSearchToolRegex20251119Type` - `const ToolSearchToolRegex20251119TypeToolSearchToolRegex20251119 ToolSearchToolRegex20251119Type = "tool_search_tool_regex_20251119"` - `const ToolSearchToolRegex20251119TypeToolSearchToolRegex ToolSearchToolRegex20251119Type = "tool_search_tool_regex"` - `AllowedCallers []string` - `const ToolSearchToolRegex20251119AllowedCallerDirect ToolSearchToolRegex20251119AllowedCaller = "direct"` - `const ToolSearchToolRegex20251119AllowedCallerCodeExecution20250825 ToolSearchToolRegex20251119AllowedCaller = "code_execution_20250825"` - `const ToolSearchToolRegex20251119AllowedCallerCodeExecution20260120 ToolSearchToolRegex20251119AllowedCaller = "code_execution_20260120"` - `CacheControl CacheControlEphemeral` Create a cache control breakpoint at this content block. - `DeferLoading bool` If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search. - `Strict bool` When true, guarantees schema validation on tool names and inputs ### Returns - `type MessageTokensCount struct{…}` - `InputTokens int64` The total number of tokens across the provided list of messages, system prompt, and tools. ### Example ```go package main import ( "context" "fmt" "github.com/anthropics/anthropic-sdk-go" "github.com/anthropics/anthropic-sdk-go/option" ) func main() { client := anthropic.NewClient( option.WithAPIKey("my-anthropic-api-key"), ) messageTokensCount, err := client.Messages.CountTokens(context.TODO(), anthropic.MessageCountTokensParams{ Messages: []anthropic.MessageParam{anthropic.MessageParam{ Content: []anthropic.ContentBlockParamUnion{anthropic.ContentBlockParamUnion{ OfText: &anthropic.TextBlockParam{ Text: "x", }, }}, Role: anthropic.MessageParamRoleUser, }}, Model: anthropic.ModelClaudeOpus4_6, }) if err != nil { panic(err.Error()) } fmt.Printf("%+v\n", messageTokensCount.InputTokens) } ``` #### Response ```json { "input_tokens": 2095 } ```