fix: allow named interfaces for structuredContent in tool callbacks#1714
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travisbreaks wants to merge 1 commit intomodelcontextprotocol:mainfrom
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fix: allow named interfaces for structuredContent in tool callbacks#1714travisbreaks wants to merge 1 commit intomodelcontextprotocol:mainfrom
travisbreaks wants to merge 1 commit intomodelcontextprotocol:mainfrom
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TypeScript does not allow named interfaces to be assigned to index signatures (Record<string, unknown>), even when all properties are compatible. This meant that returning a named interface as structuredContent in a tool callback caused a type error, while inline object types worked fine. Introduces ToolCallbackResult, which uses `object` instead of Record<string, unknown> for the structuredContent field in the callback return position. The Zod schema remains unchanged for runtime validation. Adds a compile-time type test in mcp.examples.ts verifying that named interfaces work as structuredContent without type casts. Fixes modelcontextprotocol#837 Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
🦋 Changeset detectedLatest commit: ff438df The changes in this PR will be included in the next version bump. This PR includes changesets to release 4 packages
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@modelcontextprotocol/client
@modelcontextprotocol/server
@modelcontextprotocol/express
@modelcontextprotocol/hono
@modelcontextprotocol/node
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Summary
interface MyResult { data: string }) caused a type error when returned asstructuredContentin tool callbacks, while inline object types worked fine.Record<string, unknown>index signatures, even when all properties are compatible.CallToolResult.structuredContentis typed asRecord<string, unknown> | undefined.ToolCallbackResult, a more permissive version ofCallToolResultthat usesobjectinstead ofRecord<string, unknown>for thestructuredContentfield. This type is used only in the callback return position; the Zod schema remains unchanged for runtime validation.What changed
packages/server/src/server/mcp.ts: AddedToolCallbackResulttype and updatedToolCallbackto use it instead ofCallToolResultpackages/server/src/server/mcp.examples.ts: Added a compile-time type test that verifies named interfaces work asstructuredContentwithout casts.changeset/fix-structured-content-type.md: Changeset for patch releaseTest plan
pnpm --filter @modelcontextprotocol/server testpasses (37 tests)pnpm --filter @modelcontextprotocol/test-integration testpasses (386 tests)npx tsc --noEmitpasses with zero type errors (including the new named-interface example)pnpm --filter @modelcontextprotocol/server lintpassesCallToolResultannotations continue to compile🤖 Generated with Claude Code