Fix Missing Required Client Capability error code - #15
Merged
LucaButBoring merged 1 commit intoAug 20, 2026
Merged
Conversation
The spec cites -32003 for "Missing Required Client Capability", but the canonical code is -32021: SEP-2663 uses -32021 in all four of these spots, the core 2026-07-28 schema defines MissingRequiredClientCapability Error as -32021, and the TypeScript SDK exports MISSING_REQUIRED_CLIENT_CAPABILITY = -32021. -32003 appears in no core schema version.
Contributor
|
Thank you, looks good 😄 yes, this change happened upstream in modelcontextprotocol/modelcontextprotocol#2907 and was never ported here. |
LucaButBoring
approved these changes
Aug 20, 2026
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
The spec cites
-32003for "Missing Required Client Capability". The canonical code is-32021.Evidence:
-32021, in all four of these same spots2026-07-28schema,MissingRequiredClientCapabilityError-32021draftschema-32021MISSING_REQUIRED_CLIENT_CAPABILITY-32021-32003appears in no core schema version (2025-06-18,2025-11-25,2026-07-28,draft).It looks like this came in with the SEP-2663 port in 29f83d5 — the added lines already read
-32003, whereas SEP-2663 says-32021. Supporting this, one of the affected examples carries the comment// MISSING_REQUIRED_CLIENT_CAPABILITYimmediately above the value, and that constant is exactly-32021in the TypeScript SDK.Docs-only: error codes aren't encoded in
schema.tsor the generatedschema.json, so no regeneration is needed.I noticed this while implementing the tasks extension capability negotiation in the Go SDK (modelcontextprotocol/go-sdk#755), which already implements this error as
-32021.CONTRIBUTING notes that changes should go through the Agents Working Group first. I've opened this directly since it's a factual correction rather than a design change — happy to take it to the WG instead if you'd prefer.