Graphite has revolutionized developer collaboration on code by developing a suite of tools, including Diamond, an AI-powered code reviewer that has gained traction among developers for its intelligent comments on pull requests. To ensure Diamond provides consistently actionable and relevant feedback, Graphite transitioned from manual evaluation to a systematic approach, addressing complex challenges like contextual relevance, actionability, precision, and consistency. This involved building evaluation datasets from real developer interactions and implementing custom scoring functions to refine AI performance. By leveraging Braintrust, a tool for evaluating AI model efficacy, Graphite has improved Diamond's accuracy and reliability, resulting in a 5% reduction in negative rule generation for custom coding standards. This systematic approach not only enhances the AI's feedback but also accelerates development cycles, facilitates data-driven decision-making, and fosters improved collaboration within the team, offering a model for other teams seeking to build trustworthy AI developer tools.