Better tools made Copilot code review worse. Here's how we actually improved it.

This post details how GitHub Copilot code review transitioned from using custom code exploration tools to shared CLI tools (grep, glob, view). Initially, this led to increased review costs and reduced issue detection due to the agent exhibiting broad browsing behavior. The key contribution was rewriting the tool instructions to guide the agent towards a reviewer's workflow: starting from the diff, narrowing the search with grep and glob, and then reading focused ranges with view. This workflow optimization, validated by internal benchmarks, resulted in roughly 20% lower average review cost without compromising quality.