[Schema] Refuse an invalid x-mcp-header annotation at definition time - #441
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chr-hertel merged 5 commits intoAug 18, 2026
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SEP-2243 calls a tool definition invalid when its x-mcp-header annotation is empty, is not an HTTP field name, collides case-insensitively with another, or sits on a number, array or object property - none of which can be mirrored onto a header. Nothing said so. The earliest place to is where the tool is defined, rather than on the request that trips over it.
chr-hertel
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CodeWithKyrian,
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soyuka
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August 18, 2026 06:59
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Pull request overview
Adds definition-time validation for the x-mcp-header tool-argument annotation (SEP-2243) so invalid header annotations are rejected when a Tool is constructed, rather than failing later during request/header comparisons.
Changes:
- Validate
x-mcp-headerannotations inToolinput schemas (empty/invalid field-name, case-insensitive collisions, and disallowed schema types). - Add unit coverage for valid/invalid annotations, including nesting and “unreachable” annotations under
items. - Document the behavior in the changelog for the upcoming release.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
| tests/Unit/Schema/ToolHeaderAnnotationTest.php | Adds unit tests covering accepted, refused, and intentionally-ignored x-mcp-header placements/values. |
| src/Schema/Tool.php | Implements definition-time x-mcp-header validation for annotations reachable via properties. |
| CHANGELOG.md | Notes the new definition-time refusal behavior for invalid x-mcp-header annotations. |
Suppressed comments (1)
src/Schema/Tool.php:138
checkHeaderAnnotations()claims it validates everyx-mcp-headerannotation in the input schema, but the implementation only considers annotations reachable viaproperties(seeheaderAnnotations()). Tighten the docblock to match the actual validation scope.
* Validates every `x-mcp-header` annotation in an input schema (SEP-2243).
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chr-hertel
commented
Aug 18, 2026
This was referenced Aug 18, 2026
chr-hertel
added
2026-07-28
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SEP-2243 calls a tool definition invalid when its
x-mcp-headerannotation is empty, is not an HTTP field name (CR/LF injection included), collides case-insensitively with another, or sits on anumber, array or object property — none of which can be mirrored onto a header.Nothing said so. The earliest place to say it is where the tool is defined, rather than on the request that trips over it.
This is the definition-time half of
x-mcp-header; the request-time half (walking nested properties when comparingMcp-Param-*against the body) is part of the 2026-07-28 lifecycle work and will follow separately.