fix(core): allow additional JSON Schema properties in elicitInput requestedSchema

Adds .catchall(z.unknown()) to requestedSchema, matching the pattern used
by inputSchema/outputSchema (SEP-1613). Fixes type incompatibility when
using Zod v4's .toJSONSchema() output which includes extra properties
like $schema and additionalProperties.

Fixes #1362

Author: felixweinberger

.changeset/zod-json-schema-compat.md

@@ -0,0 +1,5 @@
+---
+'@modelcontextprotocol/core': patch
+---
+
+Allow additional JSON Schema properties in elicitInput's requestedSchema type by adding .catchall(z.unknown()), matching the pattern used by inputSchema. This fixes type incompatibility when using Zod v4's .toJSONSchema() output which includes extra properties like $schema and additionalProperties.

packages/core/src/types/schemas.ts

@@ -1855,11 +1855,13 @@ 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({
+            type: z.literal('object'),
+            properties: z.record(z.string(), PrimitiveSchemaDefinitionSchema),
+            required: z.array(z.string()).optional()
+        })
+        .catchall(z.unknown())
 });
 
 /**

packages/core/test/types.test.ts

@@ -6,6 +6,7 @@ import {
     CreateMessageRequestSchema,
     CreateMessageResultSchema,
     CreateMessageResultWithToolsSchema,
+    ElicitRequestFormParamsSchema,
     LATEST_PROTOCOL_VERSION,
     PromptMessageSchema,
     ResourceLinkSchema,
@@ -983,4 +984,31 @@ describe('Types', () => {
             }
         });
     });
+
+    describe('ElicitRequestFormParamsSchema', () => {
+        test('accepts requestedSchema with extra JSON Schema metadata keys', () => {
+            // Mirrors what z.toJSONSchema() emits — includes $schema, additionalProperties, etc.
+            // See https://github.com/modelcontextprotocol/typescript-sdk/issues/1362
+            const params = {
+                message: 'Please provide your name',
+                requestedSchema: {
+                    $schema: 'https://json-schema.org/draft/2020-12/schema',
+                    type: 'object',
+                    properties: {
+                        name: { type: 'string' }
+                    },
+                    required: ['name'],
+                    additionalProperties: false
+                }
+            };
+
+            const result = ElicitRequestFormParamsSchema.safeParse(params);
+            expect(result.success).toBe(true);
+            if (result.success) {
+                expect(result.data.requestedSchema.type).toBe('object');
+                expect(result.data.requestedSchema.$schema).toBe('https://json-schema.org/draft/2020-12/schema');
+                expect(result.data.requestedSchema.additionalProperties).toBe(false);
+            }
+        });
+    });
 });