Headbox

Write your project's rules once. Every AI agent follows the same ones, instead of a pile of files drifting apart.

• One source, every vendor. The rules live in one file. Headbox writes the same block into the instruction file each agent reads: AGENTS.md, CLAUDE.md, GEMINI.md, Cursor, Copilot and Windsurf.
• Enforced, not requested. Hooks and guards run whether or not an agent remembers the rules, and a banner says plainly when enforcement cannot be proven.
• Cheap and honest about it. The always-loaded block is a few thousand characters. Every cost on the economics page is measured from the shipped CLI, and every saving is labelled an estimate.
• Nothing hand-copied. The gallery's terminal frames are the real CLI's output, regenerated on every build, so the site cannot quietly drift from the product.