API contract tester
Give it an API and its users. Get tests that catch breaking changes between the two before they ship.
API contract tester is a free AI skill for the job "Test and fix code". Give the instructions to an AI assistant that supports the required files and tools, then review its output.
Free · No account · CC BY 4.0 licence · Made by sickn33 · Level: advanced
Made by sickn33. See the original on GitHub; we copied it as it is, with its licence.
What it does
Tests that catch the moment an API change would break the programs using it, before it reaches anyone. Give it the API and a list of who calls it, and you get a small test set that checks both sides. The skill starts from the real contract, such as an OpenAPI file or documented examples, and reads the server and client code that match. It sorts each change as breaking or safe by looking at fields, required flags, empty values, allowed options, status codes, headers, paging and error shapes. Even a new optional field can break a strict client. It then builds a small matrix of sample data using fake values. Gaps are reported, not guessed.
You give it
- The API spec or documented examples
- The server and client code
- A list of known callers
- The change you plan to make
You get
- Each change marked breaking or compatible
- Tests that cover both server and client
- Sample data for success and failure cases
- A list of untested gaps
Use it when
- You renamed a response field and fear a client will break.
- The build passes but the app and server disagree at runtime.
- You need to prove a change is safe to ship.
- A bug report needs a small reproduction between two systems.
How to use it
- Add it to your AI once: download it and add the folder to Claude, ChatGPT or Codex as a skill.
- Ask for the job in your own words. Your AI opens the skill when it fits.
- It works best when your AI can run code and read your project files.