Agent Skills are Markdown files that teach AI agents like Claude Code how to perform specific tasks. The concept parallels evergreen note-taking: curated, personally written Markdown notes stored locally (e.g., ~/.claude/skills/) that agents can load as context. Key advice: avoid importing AI-generated or bulk-copied skills, as they bloat context, may contain hallucinations, and can even carry hidden malicious instructions invisible to humans but readable by agents. Personal Obsidian vaults are a natural fit since each note already functions as a skill. Skills also require ongoing maintenance—if underlying tool docs change, skills become stale. The post recommends trusting only a small set of verified skills and linking to official docs when possible.