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API Contract Testing

Checks whether API changes will break the apps and services that depend on them, using local tests.

Source Download skill
Repository
sickn33/agentic-awesome-skills
Stars
49,023
Licence
MIT
Files
1 file

What it does

When an API (the interface a server exposes to other software) changes, this skill makes the agent compare the documented contract with the real server code and the client code that calls it. The agent then writes small local tests with made-up sample data to check valid, missing, null, wrong-type and error responses, and reports whether the change is breaking or compatible. It relies on the existing test tools in the project rather than a hosted service.

Great for

  • Backend or API developers changing a response field, endpoint, event or error format
  • Teams where a client and server build fine but fail at runtime
  • Engineers investigating a reported integration regression

Skip it if

  • Production API calls or live testing without authorization, since the skill warns against this and it could affect real systems or data
  • Projects with no API schema or documented contract, because the skill depends on having one to compare against

Try asking

  • “Review this OpenAPI change and tell me whether it breaks existing mobile clients.”
  • “Write local contract tests for the invoice endpoint covering missing and null amount fields.”
  • “Our client crashes after the server added a field; find the mismatch and make a minimal reproduction.”
  • “Plan a staged migration for removing a deprecated response field.”
Step-by-step guide: how to use API Contract TestingInstall, first run, examples, tips and FAQs

Install in 3 steps

  1. 1

    Download the skill

    The ZIP contains the 1 original files, the MIT licence and an attribution note.

    api-contract-testing.zip
  2. 2

    Add it to your agent

    Claude Code (all projects)

    mkdir -p ~/.claude/skills && unzip api-contract-testing.zip -d ~/.claude/skills/

    Claude Code / Agent SDK (this project only)

    mkdir -p .claude/skills && unzip api-contract-testing.zip -d .claude/skills/

    Claude apps (web/desktop): Settings → Capabilities → Skills → Upload skill, and choose the ZIP.

  3. 3

    Ask for the task

    No special command needed — the agent reads the skill's description and loads it when your request matches. Try one of the prompts above.

Get better results

  • Give the agent the actual contract file and the relevant client and server code, not just a description.
  • Ask for the checks actually run versus checks still needing integration proof, so claims stay honest.
  • Keep any sample payloads synthetic; do not paste real customer data into the conversation.

What's inside

  • SKILL.md

Redistributed unmodified from sickn33/agentic-awesome-skills under the MIT licence. The assessment was drafted with AI from the skill's files on 2026-10-29. Skills can instruct your agent to run code — read SKILL.md and any scripts before installing.