Writing Skills Overview Writing skills IS Test-Driven Development applied to process documentation. Personal skills live in your runtime's skills directory ( on Claude Code) — see codex-tools.md or gemini-tools.md for the path on those runtimes. Codex, Copilot CLI, and Gemini CLI all also recognize as a cross-runtime alias. You write test cases (pressure scenarios with subagents), watch them fail (baseline behavior), write the skill (documentation), watch tests pass (agents comply), and refactor (close loopholes). Core principle: If you didn't watch an agent fail without the skill, you don't…