typescript-sdk/.changeset/schema-object-type-for-unions.md

@modelcontextprotocol/core
patch

Ensure standardSchemaToJsonSchema emits type: "object" at the root, fixing discriminated-union tool/prompt schemas that previously produced {oneOf: [...]} without the MCP-required top-level type. Also throws a clear error when given an explicitly non-object schema (e.g. z.string()). Fixes #1643.