Web performance best practices

Use when auditing or improving web performance with a focus on Lighthouse and Core Web Vitals.

Mental model

• Performance work is about improving the user experience, not just raising a Lighthouse score.
• Treat lab metrics and field metrics as complementary. Lighthouse helps diagnose issues in a controlled environment; field data tells you what users actually experience.
• Optimize the end-to-end path: server response, network, HTML/CSS/JS delivery, rendering, hydration, and interaction.

Core Web Vitals

• Track the current Core Web Vitals: LCP, INP, and CLS.
• Use the current “good” thresholds as a baseline:
  • LCP: 2.5s or less
  • INP: 200ms or less
  • CLS: 0.1 or less
• Evaluate at the 75th percentile and segment mobile and desktop separately when possible.