Google judges your site's performance on three Core Web Vitals — LCP, INP, and CLS — and every tool that claims to test them measures something slightly different. Use the wrong tool, and you can "fix" problems that were never hurting your rankings. These eight free tools are the ones that actually show you what Google sees.
The three metrics, in plain language
Before touching any tool, know the pass marks. LCP (Largest Contentful Paint) measures how fast your main content appears: good is under 2.5 seconds, 2.5 to 4 seconds needs improvement, and over 4 seconds is poor. INP (Interaction to Next Paint) measures how quickly your page responds when a visitor clicks or taps: good is under 200 milliseconds, 200 to 500 needs improvement, and over 500 is poor. CLS (Cumulative Layout Shift) measures visual stability while loading: good is under 0.1, 0.1 to 0.25 needs improvement, and over 0.25 is poor.
The single most important concept is the difference between field data and lab data. Field data comes from real Chrome users visiting your site — it is what Google actually uses for rankings. Lab data is a simulated test run in a controlled environment — useful for quick debugging, but it can differ from what real visitors experience. A page scoring 100 on a lab test can still fail its Core Web Vitals assessment if real users are on slow mobile connections. Always check both, and when they disagree, trust the field data.
1. Google PageSpeed Insights
The one free tool that shows field and lab data together. Enter any URL and you get a 0–100 score, the three Core Web Vitals from the Chrome UX Report (real-user data over a 28-day rolling window), and a Lighthouse lab audit with concrete diagnostics. Toggle between mobile and desktop — mobile scores are the ones that matter most, since Google indexes mobile-first. Best use: the first check on any page. If PageSpeed Insights shows your field data as poor while lab scores look fine, your problem is real-user conditions (slow devices, weak connections), not something a lab-only tweak will fix.
2. Google Search Console
PageSpeed Insights tests one page; Search Console watches your whole site. Its Core Web Vitals report groups every indexed page into Good, Needs Improvement, or Poor for mobile and desktop, powered by the same real-user field data Google's ranking systems see. This is the report that tells you a single blog post with a 4-second LCP is dragging down an entire section, even though your homepage scores perfectly. Best use: ongoing monitoring and triage. Open it monthly, note which URL groups moved, and validate fixes — but remember it aggregates data over a 28-day rolling window, so improvements take about a month to show up.
3. Lighthouse (Chrome DevTools)
Lighthouse is the lab engine behind PageSpeed Insights, and you can run it directly inside Chrome: right-click, Inspect, open the Lighthouse tab, and generate a report in seconds. The advantage over the web version is control — you can test a local build, a staging URL, or a page behind a login before it ships. It gives element-level diagnostics: exactly which image is your LCP element, which script blocks the main thread, which element shifted during load. Best use: before-and-after testing during development and CI pipelines. One caution: lab scores can swing between runs, so always compare averages, not single runs.
4. WebPageTest
When you need to know precisely what is slow, WebPageTest is the free heavyweight. Test from dozens of global locations — run your site from a server near your actual audience instead of a default US datacenter — with real connection throttling, detailed waterfall charts, and filmstrip views of exactly how the page renders frame by frame. Its waterfall is more accurate than most alternatives for diagnosing render-blocking resources, and the repeat-view option reveals how caching changes second visits. Best use: diagnosing a stubborn LCP or TTFB problem that simpler tools only hint at. It takes more technical skill to read, but the answers are the most trustworthy of any free tool.
5. GTmetrix
GTmetrix wraps a synthetic test in the friendliest reporting of any free tool: a visual waterfall chart, a request-by-request breakdown, and plain-language recommendations your clients or teammates can actually read. The free tier covers basic testing with limited options; monitoring and alerts sit on the paid Pro plan. Best use: producing client-friendly performance reports and spotting the one heavy image or slow script stalling a page. Run the same page through both GTmetrix and PageSpeed Insights — problems that appear in both are worth fixing first.
6. Pingdom Website Speed Test
The simplest read for a non-technical site owner. Enter a URL, pick a test location, and get a performance grade, total page size, request count, and load time in seconds. It will not give you Core Web Vitals with the precision of PageSpeed Insights, but it answers the question "is my site fast?" in under a minute and highlights obvious bloat like oversized pages. Best use: quick sanity checks and explaining performance to someone who will never open a waterfall chart.
7. Chrome UX Report (CrUX) Dashboard
The CrUX Dashboard is the raw source: Google's public dataset of real Chrome user experience data, visualized free through Looker Studio. It shows your site's field-data trends over time — LCP, INP, and CLS across months — so you can see whether a redesign genuinely moved the needle for real visitors. Data refreshes monthly on a 28-day rolling window. Best use: trend analysis and reporting to stakeholders. It requires a bit of setup (connecting the Looker Studio template to your origin), but once running it is the closest free window into exactly what Google's ranking sees.
8. Chrome DevTools Performance Panel
Sometimes the problem only happens when a real person interacts with the page — a janky dropdown, a delayed button. The Performance panel in Chrome DevTools lets you record a live session and trace interactions frame by frame: long tasks that block the main thread, layout thrash, expensive paint operations, and the exact interaction behind a bad INP score. Best use: root-cause analysis on interaction problems no synthetic test can reproduce. This is the most advanced tool on the list, and the one developers reach for after every simpler tool has only confirmed that a problem exists.
Which tool should you use first?
Match the tool to the job. Start with PageSpeed Insights for a one-page health check, then open Search Console to see whether the issue is site-wide. If the metrics look bad, run WebPageTest or GTmetrix for a waterfall that names the culprit, and confirm your fix with Lighthouse before deploying. For long-term proof that your work moved rankings-relevant data, watch the CrUX Dashboard and Search Console over the following month. And never optimize only your homepage — Google evaluates every indexed page, so audit the pages that earn the most organic traffic first.