Documentation and ADRs guides agents and engineers through recording the reasoning behind technical decisions, architecture choices, and public API designs. It details when and how to write Architecture Decision Records, structure inline comments that explain intent rather than restating code, document APIs with types or OpenAPI specs, and maintain project READMEs and changelogs. Reach for this skill when you need to establish project context, record constraints and trade-offs, and prevent future engineers or AI agents from rehashing past design choices.