API and Interface Design

by addyosmani

API and Interface Design is a Quality skill for Claude Code, published by addyosmani in agent-skills.

86.7K stars9.3K forkson addyosmani/agent-skillsAdded 2026/08/13Repository updated 2026/08/11

View source on GitHub Download repo ZIP

agent-skillsantigravityclaude-codecodexcursorskills

Install in seconds

Install API and Interface Design

Copy API and Interface Design into your Claude Code skills folder. Run the command in your terminal, or review the source on GitHub before installing.

terminal

npx degit https://github.com/addyosmani/agent-skills/tree/main/skills/api-and-interface-design ~/.claude/skills/api-and-interface-design

Requires Node.js. Downloads this skill only — not the rest of the repository — into your Claude Code skills folder.

Without Node.js

git clone https://github.com/addyosmani/agent-skills.git

Clones the whole repository, then copy the skill’s own directory into your skills folder yourself.

In this catalog

Source file: skills/api-and-interface-design/SKILL.md in addyosmani/agent-skills
Installs to: ~/.claude/skills/api-and-interface-design
Collection: One of 24 skills cataloged from this repository
Category: Quality — 1354 skills

What API and Interface Design does

API and Interface Design guides the creation of stable, well-documented interfaces including REST APIs, GraphQL schemas, module boundaries, and component props. Use it when designing new endpoints, defining contracts between teams, or changing existing public interfaces.

API and Interface Design is cataloged under Quality on DirSkills. API and Interface Design comes from a repository tagged agent-skills, antigravity, claude-code, codex and cursor.

Documentation

README

Excerpt

API and Interface Design

Overview

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.

When to Use

Designing new API endpoints
Defining module boundaries or contracts between teams
Creating component prop interfaces
Establishing database schema that informs API shape
Changing existing public interfaces

Core Principles

Hyrum's Law

With a sufficient number of users of an API, all observable behaviors of your system will be depended on by somebody, regardless of what you promise in the contract.

This is the opening of the README. Read the full README on GitHub.

Frequently asked about API and Interface Design

What else does addyosmani publish alongside API and Interface Design?
API and Interface Design is one of 24 skills that DirSkills catalogs from addyosmani/agent-skills, the repository it ships in. Its siblings there include Agent Skill Discovery, Browser Testing and CI/CD and Automation. Each one is a separate skill with its own page in this directory, installs the same way API and Interface Design does, and is maintained by addyosmani in that same repository. The rest of the collection is listed on the addyosmani/agent-skills page.
How does API and Interface Design compare to other Quality skills?
API and Interface Design ranks #27 by stars among the 1354 Quality skills in this catalog. The most-starred ones next to it are Benchmark, Benchmark Optimization Loop and API Design Patterns. DirSkills ranks by the star count of the repository each skill ships in, so that order reflects how popular those repositories are rather than any review of API and Interface Design against them. Open each page to compare what they document and how they install.