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Summary

  • Remove confusing "reserved by MCP" language from _meta property documentation
  • Clearly specify what keys are actually reserved: progressToken (backwards compatibility) and keys with modelcontextprotocol.* or mcp.* prefixes
  • Explicitly state that all other keys are available for arbitrary use by implementations
  • Update both draft and 2025-06-18 specification versions

This resolves the documentation ambiguity raised in the issue where "reserved" was used in conflicting ways.

Fixes #264

Remove confusing "reserved by MCP" language and clearly specify what keys are actually reserved:
- progressToken (for backwards compatibility)
- Keys with modelcontextprotocol.* or mcp.* prefixes

All other keys are available for arbitrary use by implementations.

Fixes #264
@domdomegg domdomegg requested a review from a team as a code owner August 29, 2025 12:29
@domdomegg domdomegg changed the title Clarify _meta property documentation docs: Clarify _meta property Aug 29, 2025
@domdomegg
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I think this is minor enough to not require a SEP? But happy to raise one if needed.

@domdomegg domdomegg force-pushed the adamj/clarify-meta-documentation branch from eb8a185 to 3edbc67 Compare August 29, 2025 12:33
@domdomegg domdomegg removed request for a team August 29, 2025 12:34
@localden
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This feels like it materially changes the interpretation of _meta so typically would need a SEP, but also I'd be curious if this actually impacts any servers or clients directly with the change (i.e., are there any constructs where _meta is treated as reservered today where this can introduce potential ambiguities)?

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_meta Property on CallToolResult Use is Unclear
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