An open-source project by Addy Osmani, Director at Google working on Gemini and Google Cloud (
addyosmani/agent-skills).
What it does
Coding agents produce code fast, but they don’t follow the process senior engineers do — refining the spec first, verifying with tests, checking security and performance before shipping. Prompting the process each time leads to omissions, and long guideline documents in context get skimmed rather than followed.
Agent Skills encodes that process as 24 skills. The design philosophy is “Process, not prose” — skills are workflows agents follow, not reference docs they read. Every skill carries evidence requirements like passing tests or runtime data (“Verification is non-negotiable”), and anti-rationalization tables document the common excuses agents make for skipping steps, with counter-arguments.
What’s inside
The 24 skills are organized by development lifecycle phase.
| Phase | Skills | Examples |
|---|---|---|
| Define | 3 | interview-me, idea-refine, spec-driven-development |
| Plan | 1 | planning-and-task-breakdown |
| Build | 7 | test-driven-development, context-engineering, frontend-ui-engineering, api-and-interface-design |
| Verify | 2 | browser-testing-with-devtools, debugging-and-error-recovery |
| Review | 4 | code-review-and-quality, code-simplification, security-and-hardening, performance-optimization |
| Ship | 6 | git-workflow-and-versioning, ci-cd-and-automation, documentation-and-adrs, shipping-and-launch |
Alongside the skills:
- Four specialist agent personas — code-reviewer, test-engineer, security-auditor, web-performance-auditor
- Four reference checklists — testing-patterns, security-checklist, performance-checklist, accessibility-checklist
- Hooks — session lifecycle handling
- Per-tool slash commands — 7 for Claude Code (
.claude/commands/), 7 for Gemini CLI, 8 for Antigravity
Quick start
- Add the marketplace and install the plugin —
/plugin marketplace add addyosmani/agent-skills && /plugin install agent-skills@addy-agent-skills - Work as usual — skills activate automatically based on what you’re doing. Designing an API triggers
api-and-interface-design; building UI triggersfrontend-ui-engineering. - To drive phases explicitly, use the slash commands —
/spec,/plan,/build,/test,/review,/code-simplify,/ship.
Notes
- MIT license — open-source project
addyosmani/agent-skills. - Not Claude Code-only — per-tool setup is documented in
docs/: Cursor (copy SKILL.md files into.cursor/rules/), Windsurf (rules configuration), OpenCode (AGENTS.md and the skill tool), GitHub Copilot (.github/copilot-instructions.md). - Mind the marketplace name — the plugin identifier is
agent-skills@addy-agent-skills. Running install without first adding the marketplace (/plugin marketplace add) will not find it. - Evidence-based verification — every skill specifies evidence requirements such as passing tests or runtime data, blocking the pattern where an agent just reports “done” without proof.