Lighthouse is Google’s free auditing tool, and it is probably already installed on your computer inside Chrome. In one run it scores your page for performance, accessibility, best practices and SEO, then explains every failure in plain language with links to fixes. Learning to run it properly gives you a repeatable health check for any page you own.
This guide covers the three ways to run Lighthouse, how to read the four scores, and how to act on the audits that matter most.
Quick Answer
Open your page in Chrome, press F12 to open DevTools, click the Lighthouse tab, choose Mobile, and click Analyze page load. In about 30 seconds you get scores for Performance, Accessibility, Best Practices and SEO, each backed by a list of passed and failed audits. Fix the failed performance and SEO audits first, then re-run to confirm the improvement.
Three Ways to Run Lighthouse
1. In Chrome DevTools (best for most people)
- Open the exact page you want to audit in a normal Chrome tab.
- Press F12 (or Ctrl+Shift+I) and select the Lighthouse panel.
- Pick Mobile or Desktop; mobile reflects how Google judges most sites.
- Select the categories you want and click Analyze page load.
- Wait without touching the tab; interacting skews the measurements.
2. Through PageSpeed Insights
PageSpeed Insights runs Lighthouse on Google’s servers and adds real-user field data when available. Use this when you want a result unaffected by your own machine or connection, or a shareable report link.
3. From the command line or CI
Developers can install the Lighthouse Node package to audit automatically on every deployment. Overkill for most site owners, but worth knowing it exists.
Reading the Four Scores
Performance combines metrics like Largest Contentful Paint, Total Blocking Time and Cumulative Layout Shift into one number; treat anything red as a to-do list, not a grade to mourn. Accessibility flags missing alt text, poor color contrast and unlabeled form fields: fixes here help real people and sometimes rankings. Best Practices catches outdated libraries, console errors and HTTPS problems. SEO checks the technical basics: crawlable links, meta descriptions, legible text and valid structured data. It does not judge content quality, only whether the page can be indexed and displayed properly.
Google’s own Lighthouse overview explains scoring in depth, and each audit in your report links to a web.dev explainer with remediation steps.
Acting on the Audit Like a Professional
Expand each failed audit and read the specifics: Lighthouse names the exact images that are oversized, the exact scripts that block rendering, and the exact elements with contrast problems. Sort by estimated savings, fix the top three items, and re-run. Save a PDF or screenshot of the first report so you can prove progress. Audit your homepage, a typical article and a product or contact page, because templates differ and a clean homepage can hide a broken inner template. Our SEO tools guides show the companion checks to run alongside Lighthouse.
The Audits Worth Fixing First, by Category
A report can list thirty failures; these are the ones that repay effort fastest. Under Performance: oversized images, render-blocking resources, and unused JavaScript, in that order. Under Accessibility: images without alt text, form fields without labels, and low-contrast text, because each fix is minutes of work that helps real visitors immediately. Under Best Practices: HTTPS errors and outdated JavaScript libraries with known vulnerabilities, which are security issues wearing a performance costume. Under SEO: a missing or duplicated meta description, links without descriptive text, and tap targets too close together on mobile. Fix one category’s top item per week and a neglected site transforms within a month without a single heroic weekend.
Saving and Comparing Reports Over Time
A single audit is a snapshot; two audits are a story. Save each report (DevTools lets you download the result as JSON, and a screenshot of the scores works fine) with the date and what you changed since the last one. Before any redesign, theme change or new plugin, capture a baseline; afterwards, the comparison proves whether the change helped or quietly hurt. Teams that keep this habit stop arguing about opinions, because the numbers from their own site settle the discussion. Store the reports with your other site records, and review the trend quarterly alongside your uptime and backup checks as one simple maintenance ritual.
A Gentle Glossary of the Scary Terms
Lighthouse reports intimidate newcomers mostly through vocabulary, so here are the recurring terms in plain English. Throttling means the test deliberately slows the network and CPU to imitate a mid-range phone on a mediocre connection; your real visitors vary, but the simulation makes results comparable. Emulation means the browser pretends to be a phone (screen size, touch, user agent) without being one. A render-blocking resource is a file the browser insists on downloading before showing anything, which is why deferring it unfreezes the first paint. The Opportunities section estimates seconds saved by each fix, while Diagnostics explains problems without a direct score impact, like an image that is fine but could be better. You may also notice a Progressive Web App category in DevTools; most ordinary sites can ignore it entirely. With those five ideas decoded, the entire report becomes readable, and a scary wall of audits turns into what it always was: a to-do list written by a very thorough inspector.
From Audit to Action: A 20-Minute Monthly Ritual
Tools only pay rent when they become rituals, so here is the whole discipline in one paragraph you can tape to your monitor. On the first weekday of the month, open an incognito window, run Lighthouse mobile audits on your homepage and your most-visited article, and save both reports with the date. Compare the scores with last month’s. If performance dropped more than a few points, the diff almost always traces to something added since (a plugin, an embed, a bigger hero image), and the reports’ audit lists will name it. Fix the single largest new failure, re-run to confirm, and stop. Twenty minutes, twelve times a year, is the entire cost of never being surprised by your own website’s decay, and it is why some small sites stay fast for years while prettier ones quietly rot.
Common Mistakes and Tips
Do not test while logged into WordPress or with forty tabs open; your machine’s load pollutes the result, so use an incognito window and close heavy tabs. Do not compare desktop and mobile numbers as if they were rivals; optimize mobile first. A single run can wobble, so run twice and trust the trend. And remember that third-party embeds (videos, chats, ads) drag scores down; lazy-load them rather than deleting things your business needs.
Conclusion
Lighthouse turns vague worries about speed and quality into a checklist with your page’s name on it. Run it in DevTools, fix the top failures it names, and re-run to verify. Do that monthly on your key templates and your site stays measurably healthy.
Frequently Asked Questions
Is Lighthouse the same as PageSpeed Insights?
PageSpeed Insights uses Lighthouse for its lab test and adds real-user field data on top. The audits and scoring engine are the same; the data sources differ.
What is a good Lighthouse score?
90 and above is green and healthy. Performance in the 70s and 80s is common for feature-rich WordPress pages and acceptable if your Core Web Vitals pass; below 50 needs real work.
Why do my scores change between runs?
Server response, your machine’s workload and network conditions vary. Run the audit twice, avoid using the computer during tests, and judge by the typical score.
Does Lighthouse check my whole site?
No, it audits one page at a time. Audit each important template (home, article, product, contact) because each can have different problems.
Can Lighthouse find SEO problems?
It finds technical SEO issues such as missing meta descriptions, non-crawlable links and tap targets that are too small. It cannot judge whether your content deserves to rank.
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