Generating typed request/response variants from v2026-04-08 schemas

[marcomontalbano]

We've been working on generating Zod/TypeScript models from the new JSON Schema (v2026-04-08) and found it significantly more complex than with the previous schema layout.

With the old approach, explicit request/response schema files made code generation straightforward. quicktype could produce Zod schemas with minimal custom logic.

The new schemas introduce a few challenges:

1. Request/response variants are now derived from metadata annotations, not separate files.

Instead of dedicated *_request.json / *_response.json files, field-level rules are embedded inline using ucp_request:

"ucp_request": {
  "create": "optional",
  "update": "optional",
  "complete": "omit"
}

This means a generator must interpret per-operation rules to reconstruct what was previously an explicit schema file.

2. ucp_request rules appear in nested objects.

The annotations aren't limited to top-level checkout properties, they also appear in nested types like line_item, fulfillment_method, and fulfillment_group. A generator that only handles the top level will produce incorrect schemas.

---

Having distinct Zod schemas for CreateCheckoutRequest and CreateCheckoutResponse is particularly useful when passing them as inputSchema and outputSchema of an MCP tool.

Has anyone found a clean approach to this?