Every other harness layer is powerful. But rules are the one that saves you the most time per character written. One line in a rules file saves you from repeating that instruction in every single session for the rest of the project's life.
Think about it: if you tell your agent "use Vitest, not Jest" once in a rules file, you never type that sentence again. Multiply that by 50 conventions, 200 sessions, and suddenly you've saved yourself thousands of prompts.
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Rules installed for your primary language
Rex — Rules: The Always-Follow Guidelines
Every other harness layer is powerful. But rules are the one that saves you the most time per character written. One line in a rules file saves you from repeating that instruction in every single session for the rest of the project's life.
Think about it: if you tell your agent "use Vitest, not Jest" once in a rules file, you never type that sentence again. Multiply that by 50 conventions, 200 sessions, and suddenly you've saved yourself thousands of prompts.
Ship it
Rules installed for your primary language