A Markdown File Became Our Company-Wide On-Call Cheat Code

Julian Maurin, a staff engineer at Mergify, transformed scattered tribal knowledge into a streamlined company-wide tool using Claude Code, a git-based solution to automate support investigations across six systems. Initially, Maurin faced challenges in debugging due to the complexity and undocumented nature of the processes, relying on colleagues' knowledge and his notes. By writing a detailed runbook in the CLAUDE.md file and integrating it with GitHub, the tool now allows any team member to perform comprehensive investigations in minutes by automating parallel queries across various systems like Sentry, Datadog, and Linear. The git repository not only serves as the working surface and version control but also enables the tool to access and analyze the codebase, facilitating a connection between logs and code changes. Despite initial hopes for objectivity, the AI-driven tool sometimes displays confirmation bias, focusing early on certain signals, but engineers still review its findings for reliability. The system, which evolved from Maurin's need for a support crutch, has become the team's preferred investigation method, with ongoing contributions and refinements made through familiar PR processes.