Skill Writing Skills are bundled instruction modules that load into an agent's context when activated. They are the highest-leverage mechanism for controlling agent behavior because they deliver focused instructions at the moment of relevance. The Iron Law No skill without a failing test first. Before writing a skill, run a subagent on the target task WITHOUT the skill. Document what it gets wrong — the exact rationalizations, shortcuts, and skipped steps. Then write the skill addressing those specific failures. This is TDD applied to documentation. | TDD Step | Skill Equivalent | |---|---| |…