Putting It All Together
Frontend SRE isn't a single tool — it's a stack of complementary capabilities. Understanding how they fit together helps you design a complete observability practice rather than patching gaps reactively.
| Layer | What It Monitors | Example Tools |
|---|---|---|
| Error Tracking | JavaScript exceptions, unhandled promise rejections, Error Boundary catches | Sentry, Datadog Error Tracking |
| RUM | Core Web Vitals, page load times, resource timing, user sessions | Datadog RUM, New Relic Browser, web-vitals library |
| Synthetic Monitoring | Uptime, regression detection, multi-step user flows | Datadog Synthetics, WebPageTest, Lighthouse CI |
| Session Replay | Video-like recordings of user sessions for debugging | Sentry Session Replay, LogRocket |
| Performance Budgets | CI/CD gates that fail builds exceeding size or metric thresholds | Lighthouse CI, Bundlesize, Size Limit |
Performance Budgets deserve special mention. A performance budget is a constraint you enforce in your CI/CD pipeline — for example, "fail the build if the JavaScript bundle exceeds 200KB" or "fail if Lighthouse LCP score drops below 2.5s in the synthetic test." This shifts performance from a reactive concern (users complain → you investigate) to a proactive one (the pipeline catches regressions before they ship).
A mature Frontend SRE practice connects all these layers: a performance budget catches regressions in CI, synthetic monitoring detects issues in production immediately after deploy, RUM reveals the real-world distribution of user experience, error tracking surfaces JavaScript failures, and session replay lets you watch exactly what a user experienced when something went wrong.