See what's slowing your site down.
Test any page to see how fast it loads for real visitors and in a lab run, which step is slow, and the first thing to fix.
Overall speed
What a speed test measures
Speed is not one number. It is a sequence.
When someone opens your page, the browser waits for the server, downloads files, paints, and runs scripts. A useful speed test times each step, because the slow step tells you where the fix lives.
- 1
The server answers TTFB
Time until the first byte of HTML arrives. Nothing else can start before it. A slow answer usually means uncached pages, heavy plugins or apps, redirects, or hosting far from your visitors.
- 2
Something appears FCP
The first text or image is painted. Stylesheets and scripts that block rendering, and web fonts that load late, keep the screen blank for longer.
- 3
The main content is visible LCP
The largest image or text block in view finishes rendering. This is when most visitors feel the page has loaded. Oversized hero images, images found late, and lazy loading on the first image push it back.
- 4
The page responds INP
How quickly the page reacts to taps and clicks, measured across the whole visit. Long JavaScript tasks, tag managers, and chat widgets keep the browser busy, so menus and buttons lag.
HTML document
Stylesheet
Web font
Hero image
JavaScript bundle
Chat widget
- Waiting on the server
- Downloading
- Blocks the first paint
- JavaScript running
- Third-party script
- Main thread busy: taps feel slow
Layout shift (CLS) can happen at any point in this sequence: an image without set dimensions, a late banner, or a font swap moves what the visitor was about to read or tap.
What counts as fast
Google's pass marks for the three Core Web Vitals.
Each metric is judged at the 75th percentile of real visits, separately for mobile and desktop. A page passes a metric when at least three out of four visits land in the good range.
The 0 to 100 performance score you see in Lighthouse is a separate lab score. It weighs several lab metrics together and is not one of these pass marks, so a page can score in the 90s and still fail for real visitors, or the other way round.
Diagnose by symptom
Why is my website slow? Start with what visitors notice.
Most slow pages fail in one of a few familiar ways. Match what you see to the metric that measures it, and you know who should look first.
A blank white screen before anything shows up
Slow server response: uncached pages, heavy plugins or apps, redirect chains, distant hosting.
TTFB
Hosting or developer
Text shows, but the big image or banner arrives late
An oversized or late-discovered hero image, lazy loading on the first image, render-blocking CSS.
LCP
Developer or CMS owner
Menus and buttons lag after a tap
Too much JavaScript on the main thread: large bundles, tag managers, chat, review, and ad scripts.
INP
Developer or marketer
Content jumps while you read or try to click
Images and embeds without set dimensions, late cookie banners or ads, fonts swapping in.
CLS
Developer or CMS owner
Fast on your laptop, slow for customers
Your device, connection, and cache are faster than theirs. Many visitors browse on mid-range phones over mobile networks.
Field data
Start with real-visitor data
Running a store or a CMS? See the first fixes worth checking on Shopify and WordPress.
Why speed tests disagree
One test run versus thousands of real visits.
In this example, a lab run loads the main content in 2.1 seconds and passes. Real visitors are spread out, and a quarter of them wait longer than 3.3 seconds, so the page fails for them. Neither number is wrong. They answer different questions.
- Lab test
- One run on one simulated device and network, right now. Repeatable, so it is the right tool for debugging and for checking a fix the day it ships.
- Field data
- Real Chrome visits from the Chrome UX Report over roughly the last 28 days. It shows real impact, but lags after a deploy and only exists for pages or sites with enough traffic.
This is why PageSpeed Insights, GTmetrix, and Lighthouse can show different numbers for the same page. Read why speed tools disagree, or compare nimo with PageSpeed Insights and GTmetrix.
What you get from nimo
A score says something is wrong. You need to know what.
nimo reads the real-visitor data when it exists, runs a lab test, and turns both into a short verdict with the evidence labeled and one first fix.
A typical raw result
A score, and a list of audits with no order of importance.
- Reduce unused JavaScript
- Eliminate render-blocking resources
- Properly size images
- Serve images in next-gen formats
- Reduce initial server response time
- …and more
A nimo result, example
Real visitors on phones wait too long for the main image. Loading fails Google's 2.5 second mark; responsiveness and stability pass.
- First fix
- Serve a correctly sized hero image and stop lazy-loading it.
- Why first
- The hero image is the largest element, and it starts downloading late.
- Owner
- Developer or CMS owner
- Check again
- Rerun the same test after deploy, then watch field data over the following weeks.
Example for illustration. With an account you can keep audit history, compare before and after a fix, and hand the report to your coding agent over MCP.
Get a result you can trust
How to test your website speed properly.
- 01
Test the page people land on
Your homepage is rarely the slowest page. Test the product page, landing page, or article your visitors actually arrive on.
- 02
Read the real-visitor data first
When field data exists, it is what your visitors got. The lab run explains why; it does not overrule them.
- 03
Compare values, not single scores
Lab scores move a few points between runs. Right after a fix, compare lab LCP, CLS, and TBT for the same page on the same device. INP needs real interactions, so check it in field data once new visits come in.
- 04
Change one thing, then test again
Rerun the same check after the deploy to confirm the lab numbers moved. Field data takes weeks to catch up, so keep watching it.
FAQ
Website speed test questions.
Is this website speed test free?
Yes. Enter any public page and the check runs without an account. It takes about 30 seconds and ends with the first thing to fix if the page is slow.
What is a good website speed?
Use Google's Core Web Vitals marks: the main content visible within 2.5 seconds (LCP), a response to taps and clicks within 200 milliseconds (INP), and a layout shift score of 0.1 or less (CLS). Each is judged at the 75th percentile of real visits.
Why does my speed score change every time I test?
A lab test is one run on a simulated device and network. Server load, third-party scripts, ads, and network timing vary between runs, so the score moves a few points. Compare metric values from the same page on the same device, and use field data for the real-visitor picture.
Why is my site fast for me but slow for my visitors?
Your laptop, connection, and warm browser cache are usually faster than a visitor's mid-range phone on a mobile network. Field data from real Chrome visits shows what they experienced.
Does website speed affect Google rankings?
Google says Core Web Vitals are used by its ranking systems, alongside many other signals. A faster page is better for visitors either way, but no speed test, including nimo, can promise a ranking change.
What if my site has no real-visitor data?
Smaller or newer sites may not have enough Chrome traffic for public field data. nimo labels field data as unavailable instead of guessing, uses the lab run as your baseline, and you can rerun the same check after each fix.
Want the metric details? Read about LCP, INP, CLS, and TTFB, or see what the free Core Web Vitals audit covers.
Test your website speed now.
Enter a page. Get real-visitor numbers when they exist, a lab run, and the first thing to fix.
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