fix: allow MIME type parameters in resource validation (RFC 2045) - #1755
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maxisbey merged 2 commits intoDec 9, 2025
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The MIME type validation regex was too restrictive and rejected valid RFC 2045 MIME types with parameters like `text/html;profile=mcp-app`. This is needed for MCP-UI widgets that use parameterized MIME types. The regex now supports: - Basic types: text/plain, application/json - With parameters: text/html;profile=mcp-app, application/json; charset=utf-8 - Multiple parameters: text/plain; charset=utf-8; format=fixed 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com> Github-Issue: modelcontextprotocol#1754
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Thanks for fixing this! The regex change correctly handles the common parameter cases needed for MCP Apps SDK compatibility.
One note: the regex is still more restrictive than RFC 2045 (doesn't support quoted string values like charset="utf-8"), but this covers the practical use cases. Opened #1756 to track aligning with the TypeScript SDK approach.
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maxisbey
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December 9, 2025 14:50
The resource functions are only used for metadata validation, not actually called in these tests.
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This PR is included in version v1.23.3 |
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Summary
Fixes #1754
Details
The MIME type validation regex in FastMCP's Resource class was too restrictive:
Now supports:
Test plan
🤖 Generated with Claude Code