Not a magic productivity button. If you're just getting into AI coding agents, the honest default is start with nothing. When you catch yourself correcting the same mistake three or more times, that's when a rule earns its place.
Before trying to master all of them.
Start with a short CLAUDE.md and add skills only for repeatable workflows.
Start with a couple of auto-attach rules scoped by file glob — these have near-zero token cost when you're editing unrelated code.
Write one copilot-instructions.md under 1,000 lines. If you use multiple tools, write an AGENTS.md at your repo root.
Write them like search queries. Second, keep each skill single-purpose and under ~40 lines of body content for most cases; reserve length for genuine reference material that lives in linked files.
Delete anything the model already does right, delete anything stale, delete anything contradictory. The patch spiral is real — Alex McFarland's widely-shared Substack: "Six rounds of fixes. Each round added more instructions."
Cursor shows them. Claude Code shows them. The Chroma context-rot research is clear: a rule that pushes you past 25% context fill is probably hurting output quality, not helping it. Add rules reluctantly and delete them aggressively.