The accessibility checker is not an accessibility widget
Joomla ships an accessibility plugin, and plenty of guides describe it as a toolbar giving visitors high contrast and larger text. That is not what it does.
The plugin is System - Joomla Accessibility Checker, based on Sa11y. It is aimed at the person writing the page, not the person reading it.
What it actually does
With the plugin enabled, a small button appears on the front end for logged-in users with the right permission. Press it and the page is scanned for common accessibility problems, with the offending elements highlighted in place and an explanation of how to fix each one.
It catches the things authors get wrong: images without alt text, headings that skip a level, link text that says "click here", contrast that fails, tables without headers.
What it does not do
There is no high contrast mode for visitors, no font size switcher, no grayscale toggle. Those belong to third party accessibility overlay widgets, which are a separate and much more contested subject. Joomla does not ship one.
It also does not make your site accessible. Joomla's own description is refreshingly blunt about that: the check is not exhaustive, and picking a template that is accessible in the first place matters more than any plugin.
Using it well
Turn it on during a build and leave it on while the site is being filled with content. Editors get feedback while they are writing, which is the only time fixing alt text is cheap.
The options let you choose which checks run and which parts of the page to ignore, so you can silence the warnings your template genuinely does not control and keep the ones your authors do.
The rest of the work
Keyboard navigation, focus outlines, landmarks and a sensible heading structure come from the template. Test with the keyboard alone before you ship, and be honest about what an automated check can and cannot see.
Doctor Joomla is a project of Cloudfaction, a Dutch agency building and maintaining Joomla sites since 1999. The articles are made with the help of AI, so tell us if something does not match your screen. Mail info@cloudfaction.nl if you want someone to look at yours.