Is the Contract-First API Design skill free?

Yes. The skill itself is free from robisson/build-like-amazon-agent-skills. SkillProof publishes the install command and an independent test verdict at no cost.

What is the Contract-First API Design SkillProof Score?

8.8/10 — installs cleanly 5/5, triggers reliably 5/5, output vs. baseline 8/10, docs & honesty 4/5.

How do I install Contract-First API Design?

Copy the install command from this page, run it in your terminal, and restart Claude Code. Skills live in ~/.claude/skills/ (global) or .claude/skills/ inside a project.

Can I use Contract-First API Design with Cursor, Copilot, Gemini CLI, Codex or other AI tools?

The SKILL.md format is native to Claude (Claude Code, Desktop, claude.ai). The instructions inside adapt to other assistants: Cursor rules, GitHub Copilot instructions, Windsurf rules, Custom GPTs, AGENTS.md for OpenAI Codex, and GEMINI.md for Google Gemini CLI — our conversion guides cover each, and the free converter on the tools page does the wrapping for you.

Contract-First API Design

Design the API contract before the code: versioning, idempotency, cursor paging

by robisson · robisson/build-like-amazon-agent-skills

Tested · Works

Install — copy the command Download source ↗

Test report

Verdict: Tested · Works
Score: 8.8/10
Tested: Jul 28, 2026
Environment: Claude Code 2.x (agent harness)
Upstream re-checked: Jul 30, 2026 · fe6de7c

⚠ This skill is no longer available upstream. Our re-check on Aug 10, 2026 couldn't find it any more (repo unreachable/deleted). The test below is what we measured on Jul 28, 2026 and we're leaving it up as a record — but there is nothing left to install, so we've removed the command.

Designed the same URL-shortener API twice — once cold, once following the skill body — and diffed the two contracts against a 13-point contract rubric: the cold version scored 3, the skill version 13. The skill run added the things that are breaking changes to retrofit later: a required Idempotency-Key on POST (the cold draft silently minted a second short code on retry), signed cursor pagination with a max limit instead of page/offset, machine-readable error_code plus request_id on every response, X-RateLimit-* headers, a Sunset deprecation policy and an oasdiff CI gate. It also caught a second contract surface the cold draft missed entirely — the Kafka click event needs its own AsyncAPI artifact. Cost: the skill-driven pass drifted into contract mechanics and dropped two domain rules the cold draft had (code recycling window, collision retry), so it complements rather than replaces product thinking.

Scored on four weighted criteria — install, triggering, output vs. baseline, docs. How scoring works

Installs cleanly 5/5
Triggers reliably 5/5
Output vs. baseline 8/10
Docs & honesty 4/5

What Contract-First API Design does

A doctrine skill that makes Claude write the API contract before any implementation code, picking the right standard for the protocol (OpenAPI, AsyncAPI, proto, GraphQL SDL) and pinning down versioning, error codes, idempotency keys, cursor pagination, rate-limit headers and a deprecation policy. Triggers when you ask to design a new API or endpoint, or to check whether a change breaks existing clients. No scripts, no tooling — it is a review-and-authoring checklist the model applies to your design.

How to install Contract-First API Design

Nothing to install: the source repository no longer has this skill. If the author brings it back, our daily re-check will pick it up and the command will reappear here.

Commands — how to trigger Contract-First API Design

/contract-first-api-design Design the API contract before the code: versioning, idempotency, cursor paging

It also activates on plain-language prompts like these:

Design the REST API contract for our new billing service before coding
We're adding v2 endpoints, how do we avoid breaking existing clients?
What pagination and idempotency contract should POST /payments have?

Frequently asked questions

Is the Contract-First API Design skill free?: Yes. The skill itself is free from robisson/build-like-amazon-agent-skills. SkillProof publishes the install command and an independent test verdict at no cost.
Does Contract-First API Design work with Claude Code?: We tested it with Claude Code 2.x (agent harness) on Jul 28, 2026. Verdict: Tested · Works. Designed the same URL-shortener API twice — once cold, once following the skill body — and diffed the two contracts against a 13-point contract rubric: the cold version scored 3, the skill version 13. The skill run added the things that are breaking changes to retrofit later: a required Idempotency-Key on POST (the cold draft silently minted a second short code on retry), signed cursor pagination with a max limit instead of page/offset, machine-readable error_code plus request_id on every response, X-RateLimit-* headers, a Sunset deprecation policy and an oasdiff CI gate. It also caught a second contract surface the cold draft missed entirely — the Kafka click event needs its own AsyncAPI artifact. Cost: the skill-driven pass drifted into contract mechanics and dropped two domain rules the cold draft had (code recycling window, collision retry), so it complements rather than replaces product thinking.
What is the Contract-First API Design SkillProof Score?: 8.8/10 — installs cleanly 5/5, triggers reliably 5/5, output vs. baseline 8/10, docs & honesty 4/5.
How do I install Contract-First API Design?: Copy the install command from this page, run it in your terminal, and restart Claude Code. Skills live in ~/.claude/skills/ (global) or .claude/skills/ inside a project.
Can I use Contract-First API Design with Cursor, Copilot, Gemini CLI, Codex or other AI tools?: The SKILL.md format is native to Claude (Claude Code, Desktop, claude.ai). The instructions inside adapt to other assistants: Cursor rules, GitHub Copilot instructions, Windsurf rules, Custom GPTs, AGENTS.md for OpenAI Codex, and GEMINI.md for Google Gemini CLI — our conversion guides cover each, and the free converter on the tools page does the wrapping for you.