Emit MCP tool output schemas - #6780
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tim-smart
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Jul 30, 2026
| name: tool.name, | ||
| description: Tool.getDescription(tool), | ||
| inputSchema: Tool.getJsonSchema(tool), | ||
| ...(tool.successSchema === Schema.Void || tool.successSchema === Schema.Unknown ? {} : { |
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This should check the ast instead of comparing against the schema instances
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Actually I think every tool has a valid success schema, so we could always include outputSchema. Validate this against the mcp spec first before changing anything.
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✅ No new issues found.
Reviewed changes
outputSchemafield onMcpSchema.Tool— optional JSON Schema describing the tool's output, omitted when the tool has no typed success schemaregisterToolkitemitsoutputSchema— computes and spreadsoutputSchemafor tools whosesuccessSchemais neitherSchema.VoidnorSchema.Unknown- Test for typed vs untyped — adds an
UntypedTool(defaulting toSchema.Void) and a test assertingoutputSchemaappears only for typed tools
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✅ No new issues found.
Reviewed changes
- Fixed
Schema.Void/Schema.Unknowncheck to use AST type guards — switched from===reference equality toSchemaAST.isVoid/SchemaAST.isUnknowninregisterToolkit, so annotated schemas likeSchema.Void.annotate({ description: "No output" })are correctly treated as void - Added
AnnotatedVoidTooltest coverage — new test tool withSchema.Void.annotate(...)and assertions confirming it omitsoutputSchemajust like an unadorned void tool
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tim-smart
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July 30, 2026 04:13
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Reviewed changes
- Narrowed
outputSchemagating to object-type schemas only — switched from "exclude void/unknown schemas" to "only include schemas whose JSON Schematypeis"object"", so scalar tools likeSchema.Stringno longer emitoutputSchema - Added
StructuredResultTooltest — exercises aSchema.Structtool and verifies the full object output schema withproperties,required, andadditionalProperties - Added scalar-omission assertion — verifies
OptionalStringTool(scalar) does not get anoutputSchemafield, confirming the newtype === "object"gate
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Summary
tools/listoutputSchemafor tools without typed success schemasTesting
pnpm --filter effect test --run test/unstable/ai/McpServer.test.tspnpm lint-fixpnpm checkgit diff --checkCloses EFF-226
Closes #6753