Website Optimisation · Page Speed Automation

A screenshot is not
a measurement.

Page Speed Automation measures Core Web Vitals on mobile first and reads them off the document rather than off a picture of it. That distinction is not pedantry. It is a mistake we made on this very site, diagnosed a bug that did not exist, and shipped CSS to fix it before measuring properly and reverting the lot.

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Page Speed Automation

Is it fast on a phone?

Core Web Vitals at 390px
Read off the DOM, not an image
Weight and layout shift tracked
Diane, Website Optimisation Lead
Diane · Website Optimisation Lead
Mobile is where the leak is. Our own funnel loses far more people on a phone than on a desktop.
This site: 59 KB, 1.65 seconds. The number we hold ourselves to, published rather than claimed.
Layout shift is a conversion bug. A button that moves while a thumb is travelling toward it is a lost lead.
Measured off the document. We learned this the hard way, and the story is on this page.
Early accessStatus today
DianeAgent

Part of the Website Optimisation module. Switched on and off per account, so you never pay for a module sitting idle.

This automationEarly access
How It Works

Four moves. Every one of them yours to stop.

1
Everything is measured at phone width first

Not a desktop score with a mobile tab. The layout viewport is set properly and the numbers are read from the document itself.

2
Core Web Vitals are tracked over time

A one-off score is a screenshot of a moving thing. What matters is whether it is getting worse as content is added.

3
Layout shift is treated as a conversion problem

Not a technical score. A control that moves under a thumb costs you the tap, and taps are leads.

4
Weight is budgeted, not just observed

New sections have to fit inside a budget rather than being added until someone notices the site got slow.

What You Get

The market, and what changes.

0US searches a month for core web vitals
59 KBwhat this page weighs. We hold ourselves to the number we sell
390 pxeverything measured at phone width, off the DOM, never a screenshot

Search volume: Google Keyword Planner, United States, pulled 31 Aug 2026. Every other number is measured on our own site.

The System Behind It

PostHog and the measurement harness

The measurement approach is running and it is what we use on this site: every page checked at 390px with the layout viewport set through CDP, reading scrollWidth off the document. Automatic remediation, as opposed to detection, is the early-access half.

Early accessbuilt for Ruh AI firsthuman approval on every piece
See the numbers it produced ↗
PostHog and the measurement harness
Your dataYour brand packWhat worked last month
Diane
Diane · PostHog and the measurement harness
Held for your clickrender · reviewapprove · or rejectthen it ships
Honest Limits

What this does not do yet.

Detection is solid. Automatic remediation is supervised, because a speed fix that breaks a layout is a worse outcome than a slow page.
Third-party scripts are usually the biggest cost and usually the ones you cannot remove. It will name them, it cannot delete your tag manager for you.
It measures your site. It cannot make your hosting faster.
Real-user vitals need analytics installed. Without that it is lab measurement only.
Questions

Asked before every walkthrough

Why mobile first?

Because that is where the leak is. On our own site the conversion gap between mobile and desktop was the single largest finding in the funnel.

What does measured off the document mean?

Reading scrollWidth and element geometry from the live DOM at a set viewport, rather than looking at a rendered image. Headless browsers enforce a minimum window width, so a 390px screenshot is often a crop of a wider layout. We diagnosed a bug from exactly that mistake and had to revert the fix.

Will it automatically make my site faster?

It finds and prioritises. Applying the fix is supervised, because a performance change that breaks a layout costs more than the milliseconds it saved.

Invite Only

Switch on Page Speed Automation.
Leave the rest off.

Book a walkthroughSee the Ruh AI numbers

Also in Website Optimisation: Page Drip Automation · Page Doctor