Your rules file only grows. Here's how to find the rules that do nothing

This is part 3 of a series on project rules for AI coding agents. Part 1 covered how Cursor, Claude Code, and Codex load your rules. Part 2 covered enforcing rules with hooks. This one covers the part almost nobody does: figuring out which of your rules are dead weight.

The append-only problem

Nearly every long-lived rules file I've seen has the same life story. It starts as five lines. An agent does something annoying, someone adds a rule. A bug slips through, someone adds a rule. Six months later it's 40 rules, and nobody can tell you which ones still matter.

The reason is an asymmetry in how it feels: deleting a rule feels risky, keeping it feels free. But keeping isn't free:

Context cost. Rules ship with every request. In Claude Code, CLAUDE.md is loaded into context each session; in Cursor, alwaysApply rules ride along on everything. Tokens spent on dead rules are tokens not spent on your actual code.