Structure, in place
Headings and landmark regions are outlined where they sit, each with a chip naming what it is. A page that looks well organised and turns out to be one <div> after another is immediately obvious.
- Heading levels that skip — an
h2followed by anh4. - Landmarks with no accessible name, where several of the same type exist.
- Content that sits outside any landmark at all.
Styles off
The companion to the outline: drop the page’s CSS and read what is left, in the order the content is really in. Layout can put a sidebar visually last and structurally first; without the styles there is nowhere for that to hide.
Your scroll position is preserved on the way in and out, so you come back to the paragraph you were reading rather than the top of the page.
Start with the page you are on
Install the extension, press F12 and open the Accessibility tab. No account, nothing to configure, and nothing leaves your machine.