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fix: widen requestedSchema type to accept additional JSON Schema fields #1511

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fix: widen requestedSchema type to accept additional JSON Schema fields #1511

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0c9b2bc
fix: widen requestedSchema type to accept additional JSON Schema fields
Feb 10, 2026
4844b3a
Merge branch 'main' into fix/1362-widen-elicit-schema-types
Dave-London Feb 11, 2026
9b4547d
chore: add changeset for requestedSchema type fix
Feb 11, 2026
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5 changes: 5 additions & 0 deletions .changeset/widen-requested-schema-types.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
"@modelcontextprotocol/core": patch
---

fix: widen requestedSchema type to accept additional JSON Schema fields
13 changes: 8 additions & 5 deletions packages/core/src/types/types.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -1993,11 +1993,14 @@ export const ElicitRequestFormParamsSchema = TaskAugmentedRequestParamsSchema.ex
* A restricted subset of JSON Schema.
* Only top-level properties are allowed, without nesting.
*/
requestedSchema: z.object({
type: z.literal('object'),
properties: z.record(z.string(), PrimitiveSchemaDefinitionSchema),
required: z.array(z.string()).optional()
})
requestedSchema: z
.object({
$schema: z.string().optional(),
type: z.literal('object'),
properties: z.record(z.string(), PrimitiveSchemaDefinitionSchema),
required: z.array(z.string()).optional()
})
.passthrough()
});

/**
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13 changes: 11 additions & 2 deletions packages/core/test/spec.types.test.ts
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Expand Up @@ -53,6 +53,12 @@ type MakeUnknownsNotOptional<T> =
}
: T;

// Targeted fix: in spec, requestedSchema needs index signature to match SDK's .passthrough()
// which allows additional JSON Schema fields like `additionalProperties` from Zod's .toJSONSchema()
type FixSpecRequestedSchema<T> = T extends { requestedSchema: infer R }
? Omit<T, 'requestedSchema'> & { requestedSchema: R & { [x: string]: unknown } }
: T;

// Targeted fix: in spec, treat ClientCapabilities.elicitation?: object as Record<string, unknown>
type FixSpecClientCapabilities<T> = T extends { elicitation?: object }
? Omit<T, 'elicitation'> & { elicitation?: Record<string, unknown> }
Expand Down Expand Up @@ -160,11 +166,14 @@ const sdkTypeChecks = {
sdk = spec;
spec = sdk;
},
ElicitRequestParams: (sdk: SDKTypes.ElicitRequestParams, spec: SpecTypes.ElicitRequestParams) => {
ElicitRequestParams: (
sdk: SDKTypes.ElicitRequestParams,
spec: FixSpecRequestedSchema<SpecTypes.ElicitRequestFormParams> | SpecTypes.ElicitRequestURLParams
) => {
sdk = spec;
spec = sdk;
},
ElicitRequestFormParams: (sdk: SDKTypes.ElicitRequestFormParams, spec: SpecTypes.ElicitRequestFormParams) => {
ElicitRequestFormParams: (sdk: SDKTypes.ElicitRequestFormParams, spec: FixSpecRequestedSchema<SpecTypes.ElicitRequestFormParams>) => {
sdk = spec;
spec = sdk;
},
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