Page Speed Tools: What to Use and What to Ignore

Speed matters. So does measuring it correctly. Lab tools and real-user data tell different stories. Here’s how to use them.

Lighthouse

• Lab test — Simulated environment. Consistent, reproducible.
• Use for — Development, before/after comparisons, regression testing.
• Limitation — Doesn’t reflect real user conditions. Network, device, location vary.

PageSpeed Insights

• Lab + field — Core Web Vitals from Chrome UX Report (real users) when available.
• Use for — Quick check, prioritization. Field data is gold when you have it.
• Limitation — Field data requires traffic. New sites may not have it.

WebPageTest

• Deep dive — Waterfall, filmstrip, multiple locations.
• Use for — Debugging, specific bottlenecks. More granular than Lighthouse.
• Limitation — Slower. More technical.

What to Prioritize

• LCP — Largest content. Images, fonts, server. Fix first.
• INP — Interactivity. JavaScript, main thread. Fix second.
• CLS — Layout shift. Image dimensions, dynamic content. Fix third.

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