Plan & designMIT

API and interface design

by Addy Osmani (opens in a new tab) addyosmani/agent-skills

Contract-first guidance for APIs and module boundaries: errors, validation and versioning.

Installation

Skills CLI

Skills CLI command
npx skills@latest add addyosmani/agent-skills --skill api-and-interface-design

Requires Node.js and npm. Choose your agents in the installer; add -g for a global installation.

Fieldbook review

Reviewed 27 Sept 2026

Reference guidance rather than a procedure. Covers Hyrum's Law, idempotency keys and additive change.

  • LicenceMIT
  • FrontmatterValid name and description
  • Risky patternsNone found
  • Size368 lines
  • Last checked27 Sept 2026 · 5dafd0c44a3aabf11cae5bcb34f6fcc24dfa5c01ba6e0d3176bce997f4d68bc8

What it can touch

Guidance only. Its instructions shape how the agent thinks and writes; they do not ask it to change files or run commands.

Read the source

Fieldbook links to the original instead of copying it, so you always read the version you install.

skills/api-and-interface-design/SKILL.md on GitHub (opens in a new tab)