# api-testing

A skill for writing REST and GraphQL API tests: response shape, status codes, headers, auth boundaries and timing. Useful when a quiet schema change breaks your frontend.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 1300 installs · ★ 211
- Author: kindlmann
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/petrkindlmann/qa-skills/tree/HEAD/skills/api-testing/SKILL.md
- Updated: 2026-10-22
- HTML: https://affpapa.org/en/nevibecode/skills/api-testing

## What it does

The skill covers testing APIs against a real test environment instead of a mocked stand-in. It works through Playwright's `APIRequestContext`, Supertest for Node and httpx for Python, and includes a table for manual API exploration tools: Bruno, Hurl, Hoppscotch. That table tells you which tool fits which job.

The core idea is contract over spot-checks. Rather than asserting single fields with `toHaveProperty`, you validate the whole response against a schema — Zod 4 or AJV with JSON Schema. When the API and the tests import the same schema file, any shape change fails the build right away. With Zod 4, the skill advises using native formats like `z.email()` and `z.uuid()`; the chained `z.string().email()` forms are deprecated and slated for removal. If no schema library is available and new dependencies are off the table, it suggests checking the exact key set and field types by hand in one shared helper.

Coverage means a happy path plus at least one error path per endpoint. Ready-made patterns cover CRUD lifecycles, auth flows, 400/422/429 responses, headers, pagination, file uploads, GraphQL and webhooks. Auth counts as a test surface here: a cleared client cookie does not prove the server revoked the session. For consumer-driven contract verification through Pact or a broker, this is the wrong tool — use the contract-testing skill.

## Requirements
- Works with: Playwright, Postman

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add petrkindlmann/qa-skills --skill api-testing -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/api-testing/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/api-testing/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add petrkindlmann/qa-skills --skill api-testing -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/api-testing/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add petrkindlmann/qa-skills --skill api-testing -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/api-testing/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install petrkindlmann/qa-skills api-testing
```

2. **Manually: put the files in place**
- File: `.github/skills/api-testing/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add petrkindlmann/qa-skills --skill api-testing -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/petrkindlmann/qa-skills --path skills/api-testing
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/api-testing/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add petrkindlmann/qa-skills --skill api-testing -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/petrkindlmann/qa-skills/tree/HEAD/skills/api-testing/SKILL.md

## When to use it
- catch a response shape change before the frontend breaks on it
- write a CRUD test that carries the resource id across every step
- assert 400, 422 and 429 responses together with the `retry-after` header
- log in once in a fixture and hand tests a ready API context
- diff a GraphQL introspection snapshot to spot a removed field

## Example prompts
- write tests for the order creation endpoint: happy path plus a 422 response with field details
- validate the `/api/users` response with Zod and put the schema in a shared file
- add pagination tests: first page, empty page past the boundary, invalid page size

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 300517e0b438f545.

BEGIN THIRD-PARTY FILE 300517e0b438f545
```text
---
name: api-testing
description: >-
  Test REST and GraphQL APIs with Playwright APIRequestContext, Supertest, or standalone
  HTTP clients. Covers schema validation with Zod 4/AJV, auth flow testing, CRUD lifecycle
  tests, error and header validation, pagination, and performance assertions. Use when:
  "API test," "endpoint test," "REST test," "GraphQL test," "schema validation," "Postman replacement."
  Not for: consumer-driven contract verification (Pact, broker) — use contract-testing; browser UI flows — use playwright-automation.
  Related: contract-testing, test-data-management, ci-cd-integration, playwright-automation.
license: MIT
metadata:
  author: kindlmann
  version: "2.1"
  category: automation
---

<objective>
A response that adds a nullable field or quietly drops one slips past `toHaveProperty` spot-checks and silently breaks the frontend in production. Schema-as-contract tests catch that drift in CI, not prod. This skill produces REST and GraphQL API tests that assert response shape, status codes, headers, auth boundaries, and timing — against a real test environment, not a mocked stand-in.
</objective>

## Discovery Questions

Check `.agents/qa-project-context.md` first — if it exists, use it and skip anything already answered there. Then:

1. **REST, GraphQL, or both?** REST-only suites use standard HTTP assertions. GraphQL needs query/mutation builders and benefits from an introspection-diff snapshot.
2. **Auth mechanism?** JWT, API key, OAuth 2.0, or session cookies — each needs a different fixture strategy.
3. **OpenAPI/Swagger spec available?** If yes, auto-generate Zod schemas as contracts (`orval`, `openapi-zod-client`) and consider spec-driven fuzzing with Schemathesis.

---

## Core Principles

1. **Test contracts, not implementations.** Assert on response shape, status codes, and headers — not on internal logic or database state.
2. **Schema validation catches drift before it breaks consumers.** A failing schema test means you caught a breaking change before your frontend did.
```
END THIRD-PARTY FILE 300517e0b438f545

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