Connect Claude Code to tools via MCP changedmcp
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Upstream edited this page at 5 Oct 2026 01:02 UTC, give or take a minute or two: the time comes from Anthropic’s own sitemap rather than from a commit. This site recorded the change at 5 Oct 2026 01:07 UTC.
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411411 * The `--transport` and `--header` flags also accept `-t` and `-H` short forms
412412 * Configure MCP server startup timeout using the `MCP_TIMEOUT` environment variable (for example, `MCP_TIMEOUT=10000 claude` sets a 10-second timeout)
413413 * Set a per-server tool execution timeout by adding a `timeout` field in milliseconds to that server's `.mcp.json` entry, for example `"timeout": 600000` for ten minutes. This overrides the `MCP_TOOL_TIMEOUT` environment variable for that server only
414 * Claude Code displays a warning when MCP tool output exceeds 10,000 tokens and limits output to 25,000 tokens by default. To raise the limit, set the `MAX_MCP_OUTPUT_TOKENS` environment variable (for example, `MAX_MCP_OUTPUT_TOKENS=50000`); the warning threshold is fixed. See [MCP output limits and warnings](#mcp-output-limits-and-warnings)
414 * Claude Code displays a warning when MCP tool output exceeds 10,000 tokens and limits output to 25,000 tokens by default. To change the token limit, set the `MAX_MCP_OUTPUT_TOKENS` environment variable, for example `MAX_MCP_OUTPUT_TOKENS=50000`. The warning threshold is fixed. Unless the server raises a tool's own limit, successful text results longer than 50,000 characters are saved to a file regardless of this variable. See [MCP output limits and warnings](#mcp-output-limits-and-warnings)
415415 * Use `/mcp` to authenticate with remote servers that require OAuth 2.0 authentication
416416</Tip>
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12761276* **Configurable limit**: you can adjust the maximum allowed MCP output tokens using the `MAX_MCP_OUTPUT_TOKENS` environment variable
12771277* **Default limit**: the default maximum is 25,000 tokens
12781278* **Scope**: the environment variable applies to tools that don't declare their own limit. Tools that set [`anthropic/maxResultSizeChars`](#raise-the-limit-for-a-specific-tool) use that value instead for text content, regardless of what `MAX_MCP_OUTPUT_TOKENS` is set to. Tools that return image data are still subject to `MAX_MCP_OUTPUT_TOKENS`
1279* **Over the limit**: when a result with no image content exceeds the limit, Claude Code saves it to a file and replaces it in the conversation with a message that names the file path, so Claude reads the file when it needs the content. The file goes in the session's `tool-results` directory under [`~/.claude/projects/`](/docs/en/claude-directory#cleaned-up-automatically).
1279* **Over the limit**: when a successful result with no image content exceeds the token limit, Claude Code saves it to a file and replaces it in the conversation with a message that names the file path, so Claude reads the file when it needs the content. The file goes in the session's `tool-results` directory under [`~/.claude/projects/`](/docs/en/claude-directory#cleaned-up-automatically).
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1281To increase the limit for tools that produce large outputs:
1281A call that Claude Code has [moved to a background task](#automatic-backgrounding-of-long-tool-calls) reports its result through the task notification. Two more limits apply to a call that completes in the foreground:
12821282
1283* **Character limit for text results**: for a tool that doesn't declare [`anthropic/maxResultSizeChars`](#raise-the-limit-for-a-specific-tool), Claude Code saves a successful result with no image content to a file once it's longer than 50,000 characters, whatever its token count. Setting `MAX_MCP_OUTPUT_TOKENS` doesn't change this threshold
1284* **Error results**: when a tool returns a result marked `isError: true`, Claude receives the result's text as the tool's error message. Error text longer than about 11,000 characters keeps only its first 5,000 and last 5,000 characters, with a marker between them that says how many characters were removed
1285
1286To change the token limit, set `MAX_MCP_OUTPUT_TOKENS` in your shell before starting Claude Code:
1287
12831288```bash theme={null}
12841289export MAX_MCP_OUTPUT_TOKENS=50000
12851290claude
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12881293### Raise the limit for a specific tool
12891294
1290If you're building an MCP server, you can allow individual tools to return results larger than the default persist-to-disk threshold by setting `_meta["anthropic/maxResultSizeChars"]` in the tool's `tools/list` response entry. Claude Code raises that tool's threshold to the annotated value, up to a hard ceiling of 500,000 characters.
1295If you're building an MCP server, you can allow individual tools to return results larger than the default persist-to-disk threshold of 50,000 characters by setting `_meta["anthropic/maxResultSizeChars"]` in the tool's `tools/list` response entry. Claude Code raises that tool's threshold to the annotated value, up to a hard ceiling of 500,000 characters.
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1292This is useful for tools that return inherently large but necessary outputs, such as database schemas or full file trees. Without the annotation, results that exceed the default threshold are persisted to disk and replaced with a file reference in the conversation.
1297This is useful for tools that return inherently large but necessary outputs, such as database schemas or full file trees. Without the annotation, successful results that exceed the default threshold are persisted to disk and replaced with a file reference in the conversation.
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12941299```json theme={null}
12951300{
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