This article summarizes the DEV post “Key Performance Metrics for Web Apps and How to Measure Them,” focusing on the most important signals and how to capture them.

Core metrics

  • LCP (Largest Contentful Paint): loading speed; target < 2.5s p75.
  • INP/TTI (Interaction to Next Paint / Time to Interactive): interactivity; target INP < 200ms p75.
  • FCP (First Contentful Paint): first visual response.
  • TTFB (Time to First Byte): server responsiveness.
  • Bundle size & request count: total transferred bytes and requests.

Measurement toolbox

  • Lighthouse: automated audits; budgets and suggestions.
  • WebPageTest: multi-location runs, filmstrips, waterfalls.
  • RUM (GA or custom): real-user timing for live traffic.
  • React profiler & perf tools: find slow renders/update frequency.
  • Webpack/Vite bundle analyzer: visualize bundle composition and dead weight.

Optimization reminders

  • Ship less JS/CSS; enable tree shaking/code splitting.
  • Compress and cache static assets; serve modern image formats.
  • Trim request count; inline critical CSS for hero; defer non-critical JS.
  • Watch layout stability; reserve space to avoid CLS hits.
  • Set and enforce budgets (JS gz < 200KB, LCP < 2.5s p75, INP < 200ms).

Takeaway: Track a small, high-signal set of metrics with both lab (Lighthouse/WPT) and field (RUM) data, then enforce budgets so regressions fail fast.