fix: ensure object schemas always include required field for OpenAI compatibility#1696
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…ompatibility
When using z.object({}).strict() as inputSchema, the generated JSON schema
omits the required field. OpenAI strict JSON schema mode requires required
to always be present (even as an empty array), causing tool registration
to fail with: "Schema must have the following keys: required"
Fixed in two places:
- schemaToJson() now adds required: [] to object schemas missing it
- EMPTY_OBJECT_JSON_SCHEMA constant now includes required: []
Fixes #1659
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Summary
When registering a tool with an empty Zod object (
z.object({}).strict()) asinputSchema, the generated JSON schema omits therequiredfield. OpenAI strict JSON schema mode requiresrequiredto always be present, causing:Changes
packages/core/src/util/schema.ts:schemaToJson()now checks if the output is an object type schema missingrequiredand addsrequired: [].packages/server/src/server/mcp.ts:EMPTY_OBJECT_JSON_SCHEMAconstant now includesrequired: [].Before/After
Before:
{ "type": "object", "properties": {} }After:
{ "type": "object", "properties": {}, "required": [] }Both are valid JSON Schema, but the latter is compatible with OpenAI strict mode.
Fixes #1659