You test your code. Why aren’t you testing your AI instructions?

You test your code. Why aren't you testing your AI instructions? Why instruction quality matters more than model choice, and a tool to measure it. Every team using AI coding tools writes instruction files. CLAUDE.md for Claude Code, AGENTS.md for Codex, copilot-instructions.md for GitHub Copilot, .cursorrules for Cursor. You spend time crafting these files, change a paragraph, push it, and hope for the best. Your codebase has tests. Your APIs have contracts. Your AI instructions have hope. I built agenteval to fix that. The variable nobody is testing A recent study tested three agent frameworks running the same model on 731 coding problems. Same model. Same tasks. The only difference was the instruction scaffolding. The spread was 17 points. We obsess over which model to use. Sonnet vs Opus vs GPT-5.4. But the instructions you give the model have a bigger effect on the outcome than the model itself. And nobody tests them. Think about that. You wouldn't deploy an API without tests. You