Pinterest prioritizes fighting performance regressions, using real-time user metrics to monitor and investigate issues. Proactive detection systems include A/B experiment checks, which trigger alerts and Jira tickets for significant regressions. Experiment dashboards provide top-line performance metrics, while additional dashboards allow deeper investigation of critical paths. When detailed analysis is needed, real-time debugging metrics can be enabled.Per-diff JS bundle size checks identify and prevent bundle size increases that can cause PWT regressions. These checks have reduced production regressions due to bundle size increases to near-zero. Performance integration tests are also run per-diff to detect regressions synthetically before they reach users.Key learnings from these tools include the importance of real-time user monitoring, automated proactive systems, and clear, actionable regression alerts. These systems provide early detection, isolate root causes, enable self-serve performance, and scale with increasing company growth. They have significantly reduced performance regressions, improved internal velocity, and enhanced user experience.