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docs: fix SEP-2243 base64 sentinel case-sensitivity contradiction#2937

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DaleSeo:fix/sep-2243-base64-case-sensitivity
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docs: fix SEP-2243 base64 sentinel case-sensitivity contradiction#2937
DaleSeo wants to merge 1 commit into
modelcontextprotocol:mainfrom
DaleSeo:fix/sep-2243-base64-case-sensitivity

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@DaleSeo

@DaleSeo DaleSeo commented Jun 17, 2026

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Fixes #2936

Motivation and Context

The "Base64 Decoding" conformance table tells servers to accept =?BASE64?...?= as a case-insensitive prefix. However, this contradicts the normative prose, which states that the =?base64? markers are case-sensitive and should be lowercase only.

How Has This Been Tested?

Documentation-only change.

Breaking Changes

None.

Types of changes

  • Bug fix (non-breaking change which fixes an issue)
  • New feature (non-breaking change which adds functionality)
  • Breaking change (fix or feature that would cause existing functionality to change)
  • Documentation update

Checklist

  • I have read the MCP Documentation
  • My code follows the repository's style guidelines
  • New and existing tests pass locally
  • I have added appropriate error handling
  • I have added or updated documentation as needed

Additional context

@DaleSeo DaleSeo requested review from a team as code owners June 17, 2026 16:46
@DaleSeo DaleSeo self-assigned this Jun 17, 2026
@localden localden added the rc-high-priority Related to an upcoming specification release and needs to be addressed with a high priority. label Jun 24, 2026
@localden

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Lowercase as default, and needs an update to the conformance test cc: @pcarleton

@pcarleton

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conformance is currently case sensitive so i think this is okay:
https://github.com/modelcontextprotocol/conformance/blob/1d197a9930fdf021090d7e706182ef9daf3ed5eb/src/scenarios/client/http-custom-headers.ts#L84

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SEP-2243: base64 sentinel case-sensitivity contradicts the conformance table

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