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fix: add required field to empty object schemas for OpenAI strict mode #1719

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fix: add required field to empty object schemas for OpenAI strict mode #1719

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fix: add required field to empty object schemas for OpenAI strict mod…
guoyangzhen Mar 20, 2026
23c5598
chore: add changeset
guoyangzhen Mar 20, 2026
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5 changes: 5 additions & 0 deletions .changeset/fix-openai-strict-required.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
"@modelcontextprotocol/sdk": patch
---

fix: include required field in JSON Schema when Zod .optional() is absent
17 changes: 16 additions & 1 deletion packages/core/src/util/schema.ts
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Expand Up @@ -26,7 +26,22 @@ export type SchemaOutput<T extends AnySchema> = z.output<T>;
* Converts a Zod schema to JSON Schema.
*/
export function schemaToJson(schema: AnySchema, options?: { io?: 'input' | 'output' }): Record<string, unknown> {
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@felixweinberger felixweinberger Mar 23, 2026

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This function was removed, probably needs to go to standardSchemaToJsonSchema now

return z.toJSONSchema(schema, options) as Record<string, unknown>;
const jsonSchema = z.toJSONSchema(schema, options) as Record<string, unknown>;

// OpenAI strict JSON schema mode requires the `required` field to always
// be present on object schemas, even when empty. Zod's toJSONSchema omits
// it for empty objects (e.g. z.object({}).strict()), causing tool
// registration to fail with OpenAI's strict mode.
// See: https://github.com/modelcontextprotocol/typescript-sdk/issues/1659
if (
jsonSchema.type === 'object' &&
jsonSchema.properties !== undefined &&
!Array.isArray(jsonSchema.required)
) {
jsonSchema.required = [];
}

return jsonSchema;
}

/**
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