token-counting changedbuild-with-claude/token-counting
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2121The [token counting](https://platform.claude.com/docs/en/api/messages-count-tokens) endpoint accepts the same structured list of inputs for creating a message, including support for system prompts, [tools](https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview), [images](https://platform.claude.com/docs/en/build-with-claude/vision), and [PDFs](https://platform.claude.com/docs/en/build-with-claude/pdf-support). The response contains the total number of input tokens.
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23This endpoint returns an `invalid_request_error` for a few inputs that the Messages API accepts: [server tools](https://platform.claude.com/docs/en/agents-and-tools/tool-use/server-tools) such as web search, web fetch, code execution, and tool search (every server tool except the [advisor tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/advisor-tool)), the [MCP connector](https://platform.claude.com/docs/en/agents-and-tools/mcp-connector), and `image` or `document` blocks with a `url` or `file` source. Send images and PDFs as base64 to count them. For requests that use server tools or MCP servers, the Messages API response reports the tokens used in its `usage` object.
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2325<Note>
2426 The token count is an **estimate**. In some cases, the actual number of input tokens used when creating a message might differ by a small amount.
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184186### Count tokens in messages with tools
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186188<Note>
187 [Server tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/server-tools) token counts only apply to the first sampling call.
189 Token counting supports client tools and the [advisor tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/advisor-tool). Requests that include other [server tools](https://platform.claude.com/docs/en/agents-and-tools/tool-use/server-tools) return an error. For the advisor tool, the count covers the executor's first sampling call only.
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11061108### Count tokens in messages with PDFs
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11081110<Note>
1109 Token counting supports PDFs with the same [PDF support limitations](https://platform.claude.com/docs/en/build-with-claude/pdf-support#pdf-support-limitations) as the Messages API.
1111 Token counting supports base64-encoded PDFs with the same [PDF requirements](https://platform.claude.com/docs/en/build-with-claude/pdf-support#check-pdf-requirements) as the Messages API. This endpoint doesn't support `url` or `file` document sources.
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