# API Breaking Change Detector

Cross-references C# Web API controllers/DTOs against their TypeScript/JavaScript...

- Repository: https://github.com/github/awesome-copilot (40669 stars)
- Category: Design
- License: MIT
- Last updated: 2026-10-30
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add github/awesome-copilot --skill api-breaking-change-detector -g -a claude-code -y`
Codex: `npx skills add github/awesome-copilot --skill api-breaking-change-detector -g -a codex -y`
Cursor: `npx skills add github/awesome-copilot --skill api-breaking-change-detector -g -a cursor -y`
Gemini CLI: `npx skills add github/awesome-copilot --skill api-breaking-change-detector -g -a gemini-cli -y`

## Description

Cross-references C# Web API controllers/DTOs against their TypeScript/JavaScript consumers (React, Angular, Vue, Svelte, Node.js, or hand-written/auto-generated HTTP clients like Fetch, Axios, NSwag) to catch contract drift in both directions: backend changes that break client applications (renamed/removed JSON keys, new required parameters, status code shifts) and frontend code sending fields the backend no longer reads. Works directly against source code, not exported OpenAPI spec files. Use when the user asks to check for breaking API changes, verify frontend/backend contract sync, or audit a DTO/controller change against its TypeScript/JS consumers before merging. Not for generating new API code from a spec (see openapi-to-application-code) or scaffolding new endpoints (see aspnet-minimal-api-openapi).

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# 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

1. **Discover Global JSON & Naming Policies:**
   - Check `Program.cs` or `Startup.cs` for active JSON options (e.g. `JsonNamingPolicy.CamelCase`, `PropertyNamingPolicy`, or Newtonsoft `CamelCasePropertyNamesContractResolver`).
   - Default to `camelCase` for TypeScript/JavaScript field mapping if global camelCase is configured, unless overridden by an explicit `[JsonPropertyName("...")]` attribute on the C# property.
   - Ignore C# properties annotated with `[JsonIgnore]`.

The rest: https://github.com/github/awesome-copilot/blob/HEAD/skills/api-breaking-change-detector/SKILL.md