fix mcp: improve error code detection when listing tools fails #787
Conversation
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
added 2 commits
January 14, 2026 16:44
…ty discovery When MCP servers return a -32601 (Method not found) error for unsupported capabilities like resources/templates/list, the error may be wrapped by the transport layer (e.g., Streamable HTTP). The previous code only checked for e.code === -32601, but wrapped errors have the code embedded in the message string instead. This fix checks both: 1. Direct error code property (e.code === -32601) 2. Error code in message string (contains '"code":-32601') This allows capability discovery to gracefully continue when servers don't support certain methods, instead of failing the entire discovery process.
🦋 Changeset detectedLatest commit: f6a503b The changes in this PR will be included in the next version bump. This PR includes changesets to release 1 package
Not sure what this means? Click here to learn what changesets are. Click here if you're a maintainer who wants to add another changeset to this PR |
commit: |
Contributor
|
this is very silly of the transport. Will have a look, thanks :) |
Closed
mattzcarey
approved these changes
Feb 2, 2026
mattzcarey
reviewed
Feb 2, 2026
| const errorCode = getErrorCode(e); | ||
| const errorMessage = toErrorMessage(e); | ||
| const isMethodNotFound = | ||
| errorCode === -32601 || errorMessage.includes('"code":-32601'); |
Contributor
There was a problem hiding this comment.
On second thoughts this feels like it will be too broad. Do you have an example of a server which breaks this? I'd prefer to fix this on the MCP SDK side.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
3 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.
When discovering MCP server capabilities, listing tools (and other resources) would often fail because the error code was being read incorrectly.
MCP servers return a
-32601(Method not found) error for unsupported capabilities, but the transport layer (e.g., Streamable HTTP) wraps these errors. The previous code only checked fore.code === -32601, missing cases where the code was embedded in the error message string.This fix properly detects the error in both forms, allowing capability discovery to continue gracefully instead of failing entirely.
Changes