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docs: clarify SEP-2243 HeaderMismatch error code #2992

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dsp-ant merged 1 commit into from
Jul 21, 2026
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docs: clarify SEP-2243 HeaderMismatch error code #2992

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6 changes: 6 additions & 0 deletions docs/seps/2243-http-standardization.mdx
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6 changes: 6 additions & 0 deletions seps/2243-http-standardization.md
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Expand Up @@ -780,3 +780,9 @@ Implementation requirements:
- **Server SDKs**: Provide a mechanism (attribute/decorator) for marking parameters with `x-mcp-header`
- **Client SDKs**: Implement the client behavior for extracting and encoding header values
- **Validation**: Both sides must validate header/body consistency

## Changes since SEP became Final

This SEP is preserved as a historical record of what was accepted. The list below tracks changes made to the specification after this SEP reached Final status. Refer to the current [specification](https://modelcontextprotocol.io/specification) for the authoritative, up-to-date requirements.

- **`HeaderMismatch` error code reassigned from `-32001` to `-32020`.** This SEP originally assigned `HeaderMismatch` to `-32001`. The error-code allocation update in [#2907](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2907) reassigned `HeaderMismatch` to `-32020`. All references to `-32001` above should be read as `-32020` when implementing against the current specification.
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