claude-mastery-expertlisted

# Claude Code Mastery Build better agents, skills, and workflows with Claude Code. Battle-tested patterns from building Claude Code itself, used daily at Anthropic with hundreds of skills in production. ## The Three Laws of Agent Design Before anything else, internalize these: 1. **The filesystem is how agents think.** Write to disk, grep, process. Don't stuff 100 items into context. 2. **Prompt caching is architecture, not optimization.** Design your entire system around prefix stability. 3. **Give Claude a way to verify its work.** This alone 2-3x the quality of output. ## When Building an Agent ### Action Space Design > *Consult [tool-design reference](references/tool-design.md) for the complete tool design framework.* Most agent failures are **tool design problems**, not model problems. Design tools by imagining yourself solving the problem: - **Paper** = minimal (just text output). Limited but safe. - **Calculator** = specific tools (custom tool_use). More capable but rigid. - **Computer** = bash + filesystem. Most powerful, most flexible. **Start with bash.** Claude Code started with 4 tools: read, write, edit, bash. That covers 80% of tasks. Add custom tools only when bash genuinely can't do the job. **Anti-pattern:** 50 custom tools, one for each operation. This creates a "needle in haystack" problem — the model's reasoning degrades as tool count increases. **The right question:** "What permissions and environment should I provide?" — not "What should I as