Why is my website slow, and where do I start?
Almost always three things, and almost always in this order: oversized images, render-blocking CSS and JavaScript, and a slow server response. Everything else is detail that only becomes visible once those three are handled.
The important thing is not to be fooled by the score. A PageSpeed number is a simulation on a throttled connection, not a measurement of what your visitor experiences. What is useful is not the score but the metrics underneath.
Three metrics that mean something
LCP — when the largest visible element is painted. Usually the first image or the headline. A bad LCP almost always means either a heavy image or a font being waited on.
INP — how long the page ignores a click. A bad INP means JavaScript working at the moment the person wants to act.
CLS — how much the content jumps while loading. Almost always images
without width and height, or ad slots arriving late.
Where to start
Images. One 2 MB image costs more than every other optimisation combined.
Convert to WebP, resize to the size actually displayed, add width and
height.
Render-blocking files. The browser paints nothing until it has the CSS. If that file is large, or there are several, each one is a separate request before the first pixel.
Server response. If TTFB is above ~600 ms, no front-end work will help — the wait is the server. Caching or a CDN usually fixes this, not rewriting code.
What people fix for no reason
Minification, while the page weighs 3 MB in images. Font preloading, with three fonts in total. "Optimising" third-party scripts, when there is one.
Order matters because the first item often gives more than all the rest.
A free scan shows LCP, INP and CLS from Google's own measurement, plus the specific files blocking the render.
Frequently asked
Does speed really affect rankings?
It does, less than people assume. Google describes it as a tiebreaker between pages with comparable content: the faster one wins when the content is equal. Speed does not lift weak content.
Why is my score different every time?
Because it is a simulation. The same page with no changes swings by three to five points. Watch the trend, not a single run.
What does "not enough field data" mean?
That your site has too few real Chrome visitors for Google to report on. It is not an error, just a sign that traffic is still small.
Is enabling a CDN enough?
It speeds up the response and static files, but it will not shrink a 2 MB image. A CDN helps TTFB and repeat visits, not the first paint.
Check yours
A free scan shows which of the things described here your site already does, and which it does not.