api-contract-testing

api-contract-testing is a skill for Claude Code from sickn33/agentic-awesome-skills. It costs 28 tokens per session (1,235 once invoked), scanned A, original, MIT.

A guide for designing and reviewing API contract tests between a service and its clients. An API contract is the agreed shape and behaviour of requests, responses, events, and errors.

In plain words
What is it for?
Use it when API fields, endpoints, event schemas, or error formats change, or when investigating an integration regression with provider and consumer tests.
Why use it?
It catches cases where a client and server both build successfully but disagree when communicating, and helps separate breaking changes from compatible additions.

Skill for Claude Code

Written for Claude Code: shipped in a Claude Code plugin. Also seen: mentions Codex.

Part of the agentic-awesome-skills plugin — 247 skills shipped together

Good fit Use it when API fields, endpoints, event schemas, or error formats change, or when investigating an integration regression with provider and consumer tests.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/sickn33/agentic-awesome-skills/api-contract-testing
About the project

AAS Core is a local control plane for coding agents that lets them search a large catalogue of skills, choose a stack, validate it, and create a reproducible plan. It is used to assemble and review agent workflows through its CLI, local MCP server, catalogue, plugins, and Workbench. The catalogue add-ons provide the skills, plugins, bundles, and workflows that AAS Core helps agents select and validate.

sickn33/agentic-awesome-skills · 47,729 stars · on GitHub · aaskills.tech

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.

Any agent
npx skills add sickn33/agentic-awesome-skills --skill api-contract-testing
Clone the repo
git clone --depth 1 https://github.com/sickn33/agentic-awesome-skills

Made for: Claude Code.

Or install agentic-awesome-skills, the plugin that ships this one along with the rest of its 247 skills.

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-testing

README.md
[![agentmods](https://agentmods.dev/badge/skills/sickn33/agentic-awesome-skills/api-contract-testing/github.svg)](https://agentmods.dev/skills/sickn33/agentic-awesome-skills/api-contract-testing)
Your own site
<a href="https://agentmods.dev/skills/sickn33/agentic-awesome-skills/api-contract-testing"><img src="https://agentmods.dev/badge/skills/sickn33/agentic-awesome-skills/api-contract-testing/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for api-contract-testing

Your own site · 80×15
<a href="https://agentmods.dev/skills/sickn33/agentic-awesome-skills/api-contract-testing"><img src="https://agentmods.dev/badge/skills/sickn33/agentic-awesome-skills/api-contract-testing.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 28 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,235 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
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 5.1 $0.00028 $0.01235
Opus 5.5 $0.00011 $0.00494
Sonnet 5.5 $0.00006 $0.00247
Haiku 4.5 $0.00003 $0.00123

Measured 3d ago against content hash 204dad386d8b, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

api-contract-testing 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.

Origin

Copies of this mod

1 near-identical copy found in the catalogue:

plugins/agentic-awesome-skills-claude/skills/api-contract-testing/SKILL.md · 117 lines

How it starts

The opening of the file, as written. The whole thing — 117 lines — stays where its author put it; the contents beside it link to each section on GitHub.

API Contract Testing

Overview

Turn an API change into explicit provider and consumer checks. Start from the actual contract and affected clients, then verify wire-level behavior rather than relying on generated types or a successful build. Default to local fixtures and existing test tools; this skill does not provision a testing service.

When to Use

  • A response field, endpoint, event schema or error envelope changes.
  • A client and server build successfully but disagree at runtime.
  • A team needs to distinguish a breaking change from a compatible extension.
  • A reported regression needs a minimal provider/consumer reproduction.

Do not use this as authorization to call production endpoints, bypass access controls or publish a new API version.

How It Works

1. Bind the contract and scope

Identify the provider, transport, contract source and version, known consumers and the requested behavior. Read the real OpenAPI/JSON Schema/protobuf definition or documented examples and the corresponding server/client code. Record missing consumers and stale specifications as coverage gaps; do not invent interfaces or claim complete coverage from one client.

Keep these distinct: documented schema, actual provider output, generated client types and runtime parsing. A type assertion alone is not validation. Preserve the existing protocol and test runner instead of introducing a new platform by default.

2. Classify the change

Review fields, requiredness, nullability, enum values, status codes, headers, content type, pagination and error behavior. Inspect whether clients tolerate extra fields and unknown enum values. Even an added optional field can break a strict consumer. Explicitly identify affected versions and assumptions before calling a change compatible.

For events, include duplicate delivery, ordering and version envelopes. For request changes, check serialization and server validation as well as responses.

3. Build a small test matrix

Use deterministic synthetic fixtures for:

Read the full file on GitHub · 117 lines

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 · 117 lines · 28 tokens per session scan A 204dad386d8b

Subscribe to this mod's changes

api-contract-testing is a skill published in the GitHub repository sickn33/agentic-awesome-skills (47,729 stars, last pushed yesterday), licensed MIT. It adds 28 tokens to every session and 1,235 once invoked, about $0.0001 per session on Opus 5.5. 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 2026-10-14.