10 Claude Code Skill-Writing Patterns the Docs Don't Teach You
On March 31, Anthropic accidentally shipped a source map file in their Claude Code npm package — and for a brief window, the complete TypeScript source (512,000 lines across ~1,900 files) was publicly accessible. The community archived it before Anthropic could pull it down. I spent a few days going through the built-in skills: simplify, batch, skillify, and a dozen others. Most of the community attention went to the hidden feature flags and the easter egg pet system. What caught my eye was less flashy: the way Anthropic’s engineers write their own skills differs from what the official docs teach. Claude Code Skills has two official references — the Skills docs and the Agent Skills Best Practices guide. Both are worth reading. Neither prepares you for what the built-in skills actually look like. This post distills 10 patterns that are in the source but not in the docs. Each one shows a ❌ typical doc-style approach vs ✅ the actual built-in skill approach. If you write SKILL.md files for Claude Code, these patterns change how you structure them. ...