Performance monitoring: where the PageSpeed score comes from

Uptime answers one question: is the site there? Performance answers the next one: how long does it take to be there. WP Safer measures that with Google PageSpeed Insights, stores every result, and tells you when the number moves enough to be worth your attention.

What is measured, and where you see it

Each measurement runs the page through Google PageSpeed Insights twice — once as a phone, once as a desktop browser — and keeps the score out of 100 for both, plus five of the underlying metrics: First Contentful Paint, Largest Contentful Paint, Total Blocking Time, Cumulative Layout Shift and Speed Index.

Two places show it:

• The Performance column in the site list draws one ring per site. It shows the mobile score, or the desktop score if a site has only ever been measured on desktop, and a site with no measurement shows “—”. Hover it — or tap it on a phone — and both scores appear, with a link into the site.
• The site's Pagespeed tab shows the two scores as dials, the five metrics under each, and when the measurement was taken. The footer names the source, because the number is Google's and not ours.

Green from 90, amber from 50, red below that — the same thresholds Google uses, so a score you read here and a score you read at pagespeed.web.dev mean the same thing.

The measurement happens on our server

The Refresh metrics button does not measure anything in your browser. It puts the site in a queue; the measurement itself runs on our server a moment later, and the tab shows “Measuring in the background” until the result lands. You can close the page, go to another site or sign out — the result is saved either way.

That is worth knowing for two reasons. Your own connection, laptop and browser extensions no longer affect the score, so the number does not change depending on where you happen to be reading it from. And a measurement takes between a few seconds and two minutes: nothing is lost if you leave, but nothing is instant either.

If Google cannot analyse the page, the measurement is tried once more and then recorded as failed — the tab says it could not measure the site rather than showing a bad score. This is a different request from a different place than the uptime check, so it can fail on its own: a site that blocks Google's analyser, or that is temporarily too slow for it, keeps a healthy uptime record and still has no performance score.

How often it runs on its own

Every site you have connected is measured on a schedule, once a week, without you asking. Refresh metrics is always available on top of that and jumps ahead of the scheduled queue.

Weekly is a deliberate choice, not a limit we are saving for a higher plan. The PageSpeed score of an unchanged page moves on its own: across fifty consecutive pairs of measurements on our own customers' sites, the median difference between one measurement and the next was five points, and a third of them moved by more than ten. Measuring daily does not make a site's speed clearer, it only produces a number that changes every day. A weekly measurement, read as a trend over a month, tells you something; today's measurement against yesterday's usually does not.

The e-mail when the score moves

After a scheduled measurement, WP Safer compares the new scores with the previous ones and writes to you if the mobile or the desktop score has moved by at least 20 points. The subject line carries the direction and the numbers, so you can decide whether to open it: Performance dropped on example.com: mobile 78 → 51.

Two guards keep that mail rare. A site sends at most one every fourteen days, and measurements you start yourself never send one at all — you are already looking at the result on screen. If you want to watch a site closely, press the button; the mailbox is for the changes you did not go looking for.

What the score is not

This is a lab measurement: one run, from one place, on a simulated device. It is the same method Google's own tool uses, and it has the same property — a single measurement is a sample, not a verdict. Read one number as “roughly where this site is”, and a series of them as “which way it is going”.

It also measures the address the site is connected with, not every page of it. A slow product page on a fast home page will not show up here.

Where else the number is used

PageSpeed is one of the components of the Site Health score, worth 20 of its 100 points, taken from the most recent mobile result. A result older than 30 days counts there as missing data rather than as a bad score — weekly measurement keeps it comfortably inside that window.

Measurement history is kept for 180 days. The ring and the tab always show the latest one.

Which plans

Performance measurement — the weekly schedule, the button, the tab and the score-changed e-mail — is included in every plan, Free as well.