fix(examples): return isError for input validation instead of internal error#838
Merged
ezynda3 merged 1 commit intoMay 3, 2026
Merged
Conversation
…l error The echo and add tool handlers use return nil, fmt.Errorf(...) for input validation failures (wrong type, missing argument). In the SDK, this produces -32603 (InternalError), which agents cannot recover from. Changed to mcp.NewToolResultError(...), nil which returns isError: true with a descriptive message. This matches the pattern used by the SDK's own NewTypedToolHandler and NewStructuredToolHandler, and gives agents actionable feedback they can use to self-correct. Internal errors (notification send failures) are unchanged since those represent actual server-side failures, not input validation. Fixes mark3labs#837
|
Connected to Huly®: MCP_G-403 |
Contributor
|
No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info⚙️ Run configurationConfiguration used: Repository UI Review profile: CHILL Plan: Pro Run ID: 📒 Files selected for processing (1)
WalkthroughTwo tool handlers in the example server are updated to return MCP-structured tool errors via ChangesExample Tool Error Handling
Estimated Code Review Effort🎯 2 (Simple) | ⏱️ ~10 minutes Possibly Related PRs
Suggested Reviewers
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
✏️ Tip: You can configure your own custom pre-merge checks in the settings. ✨ Finishing Touches🧪 Generate unit tests (beta)
Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out. Review rate limit: 7/8 reviews remaining, refill in 7 minutes and 30 seconds.Comment |
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.
Summary
The everything server's
echoandaddtool handlers return(nil, fmt.Errorf(...))for input validation failures (wrong type, missing argument). In the SDK, this produces-32603(InternalError), which agents cannot distinguish from a server crash.Changed to
mcp.NewToolResultError(...), nilwhich returnsisError: truewith a descriptive message the agent can act on.Before / After
echowith{"message": 42}-32603"invalid message argument"isError: true"invalid message argument: expected string"echowith{}-32603"invalid message argument"isError: true"invalid message argument: expected string"addwith{"a": "x", "b": 2}-32603"invalid number arguments"isError: true"invalid number arguments: expected numeric values"Why this matters
The everything server is the reference example. Developers learning from it copy the
return nil, fmt.Errorf(...)pattern. The SDK's ownNewTypedToolHandler(typed_tools.go:19) andNewStructuredToolHandler(typed_tools.go:32) already useNewToolResultErrorfor argument binding failures, but the untyped example teaches the opposite.Internal errors (notification send failures at lines 408, 446) are unchanged since those represent actual server-side failures.
Test plan
go build ./examples/everything/passesgo test ./... -shortpasses (all packages)isError: trueinstead of-32603Fixes #837
Summary by CodeRabbit