api-and-interface-design

api-and-interface-design is an open-source backend skill for Claude Code and compatible agents, published by addyosmani. Its author describes it as: “Guides stable API and interface design. Use when designing APIs, module boundaries, or any public interface. Use when creating REST or GraphQL endpoints, defining type contracts between modules, or establishing bounda…”. The project has 88k stars on GitHub and is available under the MIT license. Add it to your setup with `/plugin marketplace add addyosmani/agent-skills`.

What api-and-interface-design does

Design stable, well-documented interfaces that are hard to misuse. Good interfaces make the right thing easy and the wrong thing hard. This applies to REST APIs, GraphQL schemas, module boundaries, component props, and any surface where one piece of code talks to another.

Installation

Add api-and-interface-design to your agent with:

/plugin marketplace add addyosmani/agent-skills

Always review a skill's source before installing it. This command comes from the skill's public repository; the linked repo is the source of truth for exact setup steps.

What's inside

The SKILL.md for api-and-interface-design is organised into these sections:

• Overview
• When to Use
• Core Principles
• Hyrum's Law
• The One-Version Rule
• 1. Contract First
• 2. Consistent Error Semantics
• 3. Validate at Boundaries
• 4. Prefer Addition Over Modification
• 5. Predictable Naming
• 6. Honouring an Idempotency Key
• REST API Patterns

When to use it

Reach for api-and-interface-design when you want backend help from your agent without writing the same instructions every session. Load the skill and the agent picks it up automatically for relevant tasks.

Strengths

• Clear MIT license — safe to read and adapt
• Ships in addyosmani/agent-skills, an established project with 88,280 GitHub stars
• Actively maintained (recent commits)

Topics

Frequently asked questions

What does api-and-interface-design do?

Guides stable API and interface design. Use when designing APIs, module boundaries, or any public interface. Use when creating REST or GraphQL endpoints, defining type contracts between modules, or establishing boundaries between frontend and backend.

How do I install api-and-interface-design?

Run /plugin marketplace add addyosmani/agent-skills in your agent, then reload your skills. Review the source at https://github.com/addyosmani/agent-skills before installing.

Is api-and-interface-design free to use?

Yes. api-and-interface-design is free and open source under the MIT license, so you can read, run, and adapt it within that license's terms.

Where does api-and-interface-design come from?

api-and-interface-design ships inside addyosmani/agent-skills, a repository that contains 25 catalogued skills in total. The repository's 88,280 GitHub stars apply to that whole collection, not to this skill on its own.