fix: getParseErrorMessage now surfaces custom Zod v4 error messages#1663
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Vadaski wants to merge 2 commits intomodelcontextprotocol:mainfrom
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fix: getParseErrorMessage now surfaces custom Zod v4 error messages#1663Vadaski wants to merge 2 commits intomodelcontextprotocol:mainfrom
Vadaski wants to merge 2 commits intomodelcontextprotocol:mainfrom
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In Zod v4, `error.message` is a JSON serialization of the issues array
rather than a user-facing string. The previous implementation prioritized
`error.message`, which caused custom error messages defined via
`.min(1, 'My custom error')` or custom error maps to be swallowed —
callers saw a raw JSON blob instead of the human-readable message.
Fix by extracting messages from `error.issues` first, falling back to
`error.message` only when no issue messages are available.
Also update call sites in `client.ts` and `mcp.ts` that were
hand-rolling `issues.map(i => i.message).join(', ')` to use
`getParseErrorMessage` consistently.
Closes modelcontextprotocol#1415
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@modelcontextprotocol/client
@modelcontextprotocol/server
@modelcontextprotocol/express
@modelcontextprotocol/hono
@modelcontextprotocol/node
commit: |
…coercion-functions
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Problem
In Zod v4,
error.messageis a JSON serialization of the issues array rather than a user-facing string. The previous implementation ofgetParseErrorMessageprioritizederror.message, which caused custom error messages defined via.min(1, 'My custom error')or custom error maps to be completely swallowed. Instead of seeing"My custom error", callers received a raw JSON blob like:This affected tool input validation errors, output schema validation, prompt argument errors, and
listChangedoptions validation — anywhere the SDK surfaces a Zod parse failure to the developer.Closes #1415
Fix
Extract messages from
error.issuesfirst; fall back toerror.messageonly when no issue messages are available.Also updated call sites in
client.tsandmcp.tsthat were hand-rollingissues.map(i => i.message).join(', ')to usegetParseErrorMessagefor consistency.Changes
packages/core/src/util/schema.ts— fixgetParseErrorMessageto preferissue.messageover the JSON-serializederror.messagepackages/core/test/util/schema.test.ts— new test file with regression tests for custom Zod v4 messages and fallback behaviourpackages/client/src/client/client.ts— usegetParseErrorMessageinstead of rawerror.messagepackages/server/src/server/mcp.ts— usegetParseErrorMessageconsistently (3 call sites)Testing
All existing tests pass (
pnpm build:all && pnpm test:all).