api-breaking-change-detector

1# API Breaking Change Detector
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3You 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.
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5## When to use this
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7Trigger when the user asks to:
8- Check whether a DTO/controller change will break frontend or client applications
9- Verify the client and backend API contract are still in sync
10- Audit a specific endpoint, or the whole API surface, for breaking changes before a release
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12Do not use this for:
13- Generating new API code from an OpenAPI spec (see `openapi-to-application-code`)
14- Scaffolding new endpoints with OpenAPI docs (see `aspnet-minimal-api-openapi`)
15- Comparing two OpenAPI spec *files* directly — this skill reads source code, not exported specs
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17## Process
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191. **Discover Global JSON & Naming Policies:**
20   - Check `Program.cs` or `Startup.cs` for active JSON options (e.g. `JsonNamingPolicy.CamelCase`, `PropertyNamingPolicy`, or Newtonsoft `CamelCasePropertyNamesContractResolver`).
21   - Default to `camelCase` for TypeScript/JavaScript field mapping if global camelCase is configured, unless overridden by an explicit `[JsonPropertyName("...")]` attribute on the C# property.
22   - Ignore C# properties annotated with `[JsonIgnore]`.
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242. **Identify the C# contract surface.** For each Controller action in scope:
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