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Performance

Lighthouse Score

Google Lighthouse

Portrait of Lukas Horvath, co-founder of Roelu Studio
Lukas HorvathCo-founder

What is Lighthouse Score?

A Lighthouse score is a 0–100 grade produced by Google Lighthouse, an open-source auditing tool built into Chrome DevTools. It scores a page across four categories: Performance, Accessibility, Best Practices, and SEO. The Performance score is weighted across Core Web Vitals and other metrics like Total Blocking Time and Speed Index. Google considers 90 or above good, 50 to 89 needs improvement, and below 50 poor.

Why it matters

Lighthouse scores are useful and overrated in equal measure. They're useful because they catch obvious issues — unoptimised images, missing alt text, render-blocking scripts — in 30 seconds. They're overrated because the score is generated in a lab, on simulated hardware, on a single page load. The number can swing 15 points between runs on the same page. We've watched marketing teams celebrate hitting 100 on the homepage while every other page in the funnel sits at 60. The score is a starting point. The real measure is field data from real visitors. Use Lighthouse to find problems. Use Core Web Vitals to confirm you've fixed them.

How it works

You run Lighthouse in Chrome DevTools, in the PageSpeed Insights web tool, or via the command line. It loads the page in a simulated environment, runs a battery of audits, and produces a score for each category plus a list of actionable diagnostics — every issue is linked to a specific fix. For a senior dev team, the diagnostics list is more useful than the score. It tells you exactly what's costing you milliseconds: which images are unoptimised, which scripts are blocking, which fonts are loading wrong. Fix the items at the top of the list, rerun, repeat. A Roelu-built site routinely scores 95+ on Performance and 100 on SEO.

Related terms

  • PageSpeed Insights

    Performance

    Google's free tool for measuring how fast a page loads on mobile and desktop, combining real-user field data with lab tests and offering specific, actionable…

  • Core Web Vitals

    Performance

    Google's three benchmark metrics that measure how fast a page loads, how quickly it responds to clicks, and how stable the layout feels as it renders — used in…

  • Page Speed

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    How quickly a web page loads and becomes usable for a visitor — measured in seconds and milliseconds, and treated by Google as a confirmed ranking signal…

  • Accessibility

    Design & UX

    Designing and building a website so people with disabilities — vision, hearing, motor, cognitive — can actually use it, not just open it, and so the rest of…

  • SEO Audit

    SEO/AEO/GEO

    A structured review of a website's SEO health — covering technical setup, on-page content, backlinks, and rankings — to find what's broken, what's missing, and…

  • Largest Contentful Paint

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    The Core Web Vital that measures how long it takes for the biggest visible element on a page — usually the hero image or main headline — to finish loading in…

  • Technical SEO

    SEO/AEO/GEO

    The plumbing of SEO — making sure search engines can crawl, render, and index your site quickly and cleanly, so your content actually has a chance to rank…