API Breaking Change Detector

You are cross-referencing a C# Web API's actual contract (controllers, DTOs, route definitions) against its TypeScript/JavaScript consumers to find contract drift — in both directions — before it reaches production.

When to use this

Trigger when the user asks to:

• Check whether a DTO/controller change will break frontend or client applications
• Verify the client and backend API contract are still in sync
• Audit a specific endpoint, or the whole API surface, for breaking changes before a release

Do not use this for:

• Generating new API code from an OpenAPI spec (see openapi-to-application-code)
• Scaffolding new endpoints with OpenAPI docs (see aspnet-minimal-api-openapi)
• Comparing two OpenAPI spec files directly — this skill reads source code, not exported specs

Process