fix mcp: improve error code detection when listing tools fails#787
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kooba wants to merge 3 commits intocloudflare:mainfrom
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fix mcp: improve error code detection when listing tools fails#787kooba wants to merge 3 commits intocloudflare:mainfrom
kooba wants to merge 3 commits intocloudflare:mainfrom
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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.
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this is very silly of the transport. Will have a look, thanks :) |
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mattzcarey
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Feb 2, 2026
mattzcarey
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Feb 2, 2026
| const errorCode = getErrorCode(e); | ||
| const errorMessage = toErrorMessage(e); | ||
| const isMethodNotFound = | ||
| errorCode === -32601 || errorMessage.includes('"code":-32601'); |
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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.
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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.
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