The word tool covers three very different things in this field, and confusing them is expensive. There are testing tools that inspect your pages and report; there are authoring tools that help you produce accessible content; and there are overlays and toolbars that inject a script into your live site and change what visitors see. Only the first two are what this hub is about. This page is what each does, and why the third is a separate decision with its own risks.
Testing tools: what they report and what they miss
Browser extensions and CI scanners check the machine-decidable criteria and are worth running on every template and every pull request. They will not tell you whether a control is usable, and a clean scan on an unusable page is the most common false comfort in this field. On the worked example the manual half is 11 hours of an auditor's time against 240 pages.
Authoring tools: where the long tail is prevented
The CMS field that makes alt text required, the design tool plugin that checks contrast, the editor that will not let a heading level be skipped. These stop issues being created, which is the only way the content long tail stops regrowing after a remediation programme ends.
Overlays and toolbars: a different decision
A web accessibility toolbar or overlay injects a script that changes the rendered page: contrast switches, font sizing, sometimes generated alt text. It does not change your code, it does not fix the underlying markup, and installed overlays have appeared in the litigation this field produces. If you buy one, buy it knowing it is a visitor-facing widget rather than a fix, and keep the remediation programme.
Questions people ask about ada tools
Does an overlay make a site ADA compliant?
No product can make that claim honestly, and the run-time approach has been contested repeatedly. Fix the code.
Which testing tool is best?
The one your team will run every build. Overlap between the main engines is high.
Are browser extensions enough for an audit?
For the automated third, yes. The rest needs a keyboard, a screen reader and a person.