Is the API Designer skill free?

Yes. The skill itself is free from Jeffallan/claude-skills. SkillProof publishes the install command and an independent test verdict at no cost.

What is the API Designer SkillProof Score?

7.2/10 — installs cleanly 5/5, triggers reliably 4/5, output vs. baseline 5/10, docs & honesty 4/5.

How do I install API Designer?

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 API Designer 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.

API Designer

Designs REST or GraphQL APIs with resource models, versioning, and error standards.

by Jeffallan · Jeffallan/claude-skills

Works with setup

Install — copy the command Download source ↗

Test report

Verdict: Works with setup
Score: 7.2/10
Tested: Jul 12, 2026
Environment: Claude Code 2.x (agent harness)
Upstream re-checked: Aug 10, 2026 · 9d68465

Installed verbatim (target redirected to workdir): SKILL.md frontmatter is strict-YAML-valid and all five reference files (rest-patterns, versioning, pagination, error-handling, openapi) are present and substantial. On a Bookmarks REST API design task the skill produced a correct, complete result — noun-only URIs, cursor pagination with justification, valid OpenAPI 3.1, and an RFC 7807 error. A/B vs the no-skill base arm was a wash: both hit every requirement at essentially equal quality, so the skill adds solid guardrails but no transformative lift here.

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

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

What API Designer does

Use when designing REST or GraphQL APIs, creating OpenAPI specifications, or planning API architecture. Invoke for resource modeling, versioning strategies, pagination patterns, error handling standards.

How to install API Designer

git clone https://github.com/Jeffallan/claude-skills
cd claude-skills
mkdir -p ~/.claude/skills
cp -r skills/api-designer ~/.claude/skills/api-designer

Skills live in ~/.claude/skills/ (global) or .claude/skills/ (per-project). Restart Claude Code after installing.

Commands — how to trigger API Designer

/api-designer Designs REST or GraphQL APIs with resource models, versioning, and error standards.

It also activates on plain-language prompts like these:

Design a REST API for this new service
Write an OpenAPI spec for these endpoints
Plan pagination and error handling for this API

Frequently asked questions

Is the API Designer skill free?: Yes. The skill itself is free from Jeffallan/claude-skills. SkillProof publishes the install command and an independent test verdict at no cost.
Does API Designer work with Claude Code?: We tested it with Claude Code 2.x (agent harness) on Jul 12, 2026. Verdict: Works with setup. Installed verbatim (target redirected to workdir): SKILL.md frontmatter is strict-YAML-valid and all five reference files (rest-patterns, versioning, pagination, error-handling, openapi) are present and substantial. On a Bookmarks REST API design task the skill produced a correct, complete result — noun-only URIs, cursor pagination with justification, valid OpenAPI 3.1, and an RFC 7807 error. A/B vs the no-skill base arm was a wash: both hit every requirement at essentially equal quality, so the skill adds solid guardrails but no transformative lift here.
What is the API Designer SkillProof Score?: 7.2/10 — installs cleanly 5/5, triggers reliably 4/5, output vs. baseline 5/10, docs & honesty 4/5.
How do I install API Designer?: 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 API Designer 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.