api-contract-tester

api-contract-tester is a skill for Claude Code, Codex from chama-x/GroundRules. It costs 32 tokens per session (251 once invoked), scanned A, original, MIT.

A tool for checking whether an API's implementation still matches its formal description. An API is the agreed interface through which software exchanges requests and responses; the description may be an OpenAPI or GraphQL schema.

In plain words
What is it for?
It helps generate contract tests, mock servers, and clients from API schemas, detect drift, identify breaking changes in build pipelines, and regenerate clients in several programming languages.
Why use it?
Changes to an API can silently break applications that use it. Schema-based tests and comparison checks expose incompatible changes before they reach users.

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/chama-x/groundrules/api-contract-tester
Any agent
npx skills add chama-x/GroundRules --skill api-contract-tester
Clone the repo
git clone --depth 1 https://github.com/chama-x/GroundRules

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-contract-tester

README.md
[![agentmods](https://agentmods.dev/badge/skills/chama-x/groundrules/api-contract-tester.svg)](https://agentmods.dev/skills/chama-x/groundrules/api-contract-tester)
Your own site
<a href="https://agentmods.dev/skills/chama-x/groundrules/api-contract-tester"><img src="https://agentmods.dev/badge/skills/chama-x/groundrules/api-contract-tester.svg" alt="Measured on agentmods" height="20"></a>
Per session 32 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 251 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. 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 $0.00032 $0.00251
Opus 5 $0.00016 $0.00125
Sonnet 5 $0.00006 $0.00050
Haiku 4.5 $0.00003 $0.00025

Measured 3d ago against content hash 339a30d7d20a, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

api-contract-tester scanned grade A with 0 findings 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 3d 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.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.agents/skills/api-contract-tester/SKILL.md · 24 lines

What it actually says

API Contract Tester

You are an expert in API Contract Testing.

1. Schema-Driven Testing

  • Always use OpenAPI 3.x or GraphQL schemas as the absolute source of truth.
  • Generate mock responses directly from the schema definitions using tools like Prism or WireMock.

2. Preventing Drift

  • Implement Consumer-Driven Contract Testing (e.g., Pact) to ensure backend API changes do not break frontend consumers.
  • Run drift-detection scripts in CI that compare the generated schema hash against the committed schema.

3. Breaking Change Checks

  • Use openapi-diff or graphql-inspector in PR pipelines to fail builds if a breaking change (e.g., removing a field, making an optional field required) is detected without a major version bump.

4. Multi-language Client Generation

  • Use openapi-generator-cli or graphql-codegen to automatically regenerate SDKs.
  • Ensure generated clients are strongly typed and handle network errors gracefully.
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. 3d ago First seen · 24 lines · 32 tokens per session scan A 339a30d7d20a

Subscribe to this mod's changes

api-contract-tester is a skill published in the GitHub repository chama-x/GroundRules (5 stars, last pushed 20d ago), licensed MIT. It adds 32 tokens to every session and 251 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.