api-testing

api-testing is a skill for Claude Code, Codex from petrkindlmann/qa-skills. It costs 129 tokens per session (2,418 once invoked), scanned A, original, MIT.

A guide for checking REST and GraphQL APIs, which are interfaces that let software exchange data over HTTP. It covers both automated requests and checks that responses match the expected shape and rules.

In plain words
What is it for?
Use it to test login and permissions, create/read/update/delete operations, status codes, headers, response schemas, GraphQL queries, and response-time limits with Playwright, Supertest, or HTTP clients.
Why use it?
It catches broken response formats, authentication problems, invalid errors, pagination mistakes, and slow endpoints before they affect users or other applications.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/petrkindlmann/qa-skills/api-testing
Any agent
npx skills add petrkindlmann/qa-skills --skill api-testing
Clone the repo
git clone --depth 1 https://github.com/petrkindlmann/qa-skills

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for api-testing

README.md
[![agentmods](https://agentmods.dev/badge/skills/petrkindlmann/qa-skills/api-testing.svg)](https://agentmods.dev/skills/petrkindlmann/qa-skills/api-testing)
Your own site
<a href="https://agentmods.dev/skills/petrkindlmann/qa-skills/api-testing"><img src="https://agentmods.dev/badge/skills/petrkindlmann/qa-skills/api-testing.svg" alt="Measured on agentmods" height="20"></a>
Per session 129 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,418 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00129 $0.02418
Opus 5 $0.00064 $0.01209
Sonnet 5 $0.00026 $0.00484
Haiku 4.5 $0.00013 $0.00242

Measured 4d ago against content hash 075520dac51d, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

api-testing scanned grade A with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 4d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

| **Hurl** (8.x) | Plain-text HTTP testing, CI smoke checks | One file = many requests + assertions; runs anywhere curl runs; certificate + JSONPath (RFC 9535) queries |
skills/api-testing/SKILL.md · 166 lines

How it starts

The opening of the file, as written. The whole thing — 166 lines — stays where its author put it; the contents beside it link to each section on GitHub.

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.
  3. Auth flows are tests too — don't just hardcode tokens. Test login, refresh, expiration, and permission boundaries.
  4. Response time is a testable assertion. Performance regressions caught in CI are cheaper than production incidents.

Exploratory vs Automated: Tooling

API exploration (debugging, manual probing, OpenAPI playground) and automated API testing are different jobs. Use the right tool for each:

Tool Best for Why
Bruno (v3.4+) File-based collections, git-reviewable workflows, FOSS Postman replacement Filesystem-first, no cloud sync required; gRPC + OAuth + GraphQL query builder
Hurl (8.x) Plain-text HTTP testing, CI smoke checks One file = many requests + assertions; runs anywhere curl runs; certificate + JSONPath (RFC 9535) queries
Hoppscotch Web-based Postman-style exploration Open source, runs in browser, good for quick checks
Playwright APIRequestContext Automated tests in your test runner This skill's focus — covered below
Supertest (Node) / httpx (Python) In-process API tests against your own app Fastest feedback when you control both sides

Read the full file on GitHub · 166 lines

Files

What ships with it

3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 4d ago First seen · 166 lines · 129 tokens per session scan A 075520dac51d

Subscribe to this mod's changes

api-testing is a skill published in the GitHub repository petrkindlmann/qa-skills (107 stars, last pushed 2mo ago), licensed MIT. It adds 129 tokens to every session and 2,418 once invoked, about $0.0006 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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