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    API Contract Tester

    by Arnstein Larsen

    Turns an OpenAPI/Swagger spec into an exhaustive, framework-ready test suite — happy-path, validation, contract-conformance, auth, and defensive security tests — with a coverage matrix mapping every endpoint, status code, and schema constraint to a test.

    Updated Jun 2026
    Security scanned
    Cursor

    $5

    · or 25 credits

    30-day refund guarantee

    Secure checkout via Stripe

    Included in download

    • Generate framework-ready test suites from OpenAPI or Swagger specs.
    • Audit existing test suites to identify untested paths and schema drift.
    • browser automation included
    • Ready for Cursor
    • Instant install

    Sample input

    Generate a Jest and Supertest suite for my users.yaml OpenAPI spec. It uses Bearer token auth. Ensure we test that a user can't read another user's profile.

    Sample output

    I've generated a 12-test suite.

    | Endpoint | Method | Case | Assertion | Test ID | |---|---|---|---|---| | /users/{id} | GET | IDOR | 403 on different user's ID | T-009 |

    test('GET /users/:id - IDOR protection', async () => {
  const res = await request(app)
    .get('/users/999')
    .set('Authorization', `Bearer ${userAToken}`);
  expect(res.status).toBe(403);
});

    About This Skill

    Streamline Your API Reliability

    The API Contract Tester is a specialized skill for developers and QA engineers who need to move beyond basic smoke tests. It transforms OpenAPI/Swagger specifications into exhaustive, framework-ready test suites that cover the "dark corners" of your API—validation logic, authz boundaries, and schema conformance.

    What it does

    This skill operates in two high-impact modes:

    • GENERATE: Builds a complete test repository from a spec or description. It goes deep, creating tests for happy paths, negative input validation, schema strictness, authentication/authorization, and defensive security cases.
    • AUDIT: Analyzes your existing test suite against your contract to find "silent killers"—untested status codes, response bodies that aren't validated against schemas, and missing edge cases that lead to production outages.

    Supported Tools & Frameworks

    The skill adapts to your stack, generating idiomatic code for frameworks like Jest/Supertest, Pytest/HTTPX, Playwright API, RestAssured, Vitest, and more. It focuses on REST/JSON architectures where contract drift is the primary risk.

    Why use this skill?

    Manual test writing often misses the boring but critical negative cases. This skill automates the creation of 4xx and 5xx test scenarios, ensures every documented schema constraint is actually checked, and identifies IDOR vulnerabilities. The output is a runnable, professional-grade test suite with a coverage matrix that maps every endpoint and status code to a specific test ID.

    Use Cases

    • Generate framework-ready test suites from OpenAPI or Swagger specs.
    • Audit existing test suites to identify untested paths and schema drift.
    • Create negative test cases for every validation constraint in your API.
    • Verify authorization and IDOR protection across all protected endpoints.
    • Produce a coverage matrix mapping endpoints to specific test IDs.

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    Security Scanned

    Passed automated security review

    Permissions

    Browser

    File Scopes

    api-contract-tester/**

    Tags

    api-testing
    openapi
    contract-testing
    jest
    pytest
    qa-automation

    Works with any SKILL.md-compatible agent (Claude Code, Cursor, Codex CLI, Gemini CLI). Best with an OpenAPI/Swagger doc or Postman collection; reconstructs the contract from a prose description if needed. Defensive testing only.

    Creator

    Arnstein Larsen

    Frequently Asked Questions

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