Automated tools are a genuinely useful first step, as long as you know what they can and can’t catch. Here’s an honest rundown.
What automated tools are good at
Automated scanners are fast, free, and excellent at catching specific, checkable problems: missing alt text, insufficient colour contrast, missing form labels, a missing page language attribute, and similar structural issues. Running one takes seconds and it’s a genuinely good habit to build.
The tools themselves
- WAVE: a free browser extension that overlays your page with icons showing errors, warnings and structural information directly where the problem is. Good for a quick visual sense of where issues sit on the page.
- axe DevTools: a free browser extension built into many developers’ workflow, known for a low false-positive rate. A solid choice if you want fewer things to double-check.
- Google Lighthouse: built into Chrome’s developer tools already, so no install needed. Gives you an accessibility score alongside performance and SEO scores, which is a handy way to see accessibility sitting next to metrics you may already track.
What none of them can tell you
This is the part that matters most, and it’s not a knock on the tools. It’s just the nature of automated testing. A scanner can tell you an image is missing alt text. It cannot tell you whether the alt text you did write actually makes sense, or whether your tab order is logical, or whether a screen reader announces your form correctly, or whether an error message is genuinely understandable to a real person hitting it for the first time. Those all require a person to actually try using the site the way someone with disability would.
This is a widely acknowledged limit of automated testing, not a fringe opinion. Most of the accessibility industry agrees automated tools catch a meaningful minority of the total picture, not the majority.
What free scanners miss: real examples
Every one of these problems can pass an automated scan and still stop someone from using your website:
- Alt text that says nothing useful. A scanner sees that alt text exists. It can’t tell that “IMG_2034” or “photo” doesn’t describe the image. Our step-by-step guide to alt text shows what good alt text looks like.
- Keyboard traps and focus order. A pop-up you can open with the keyboard but can’t close, or a tab order that jumps around the page, won’t show up in a scan.
- Focus you can’t see. Scanners rarely check whether keyboard users can see where they are on custom buttons, menus and sliders.
- Colour contrast on images and hover states. Text over photos, gradients, and colours that change on hover or focus are usually skipped. See our guide to fixing low contrast text.
- Error messages screen readers don’t announce. A form can have labels and still leave a screen reader user with no idea why it won’t submit.
- Headings that only look like headings. Bold text styled to look like a heading passes a scan but gives screen reader users nothing to navigate by.
- Link text that makes no sense on its own. Several “Read more” links on one page may not be flagged, but they are confusing in a screen reader’s list of links.
- Zoom and small screens. Content that overlaps or disappears at 200% or 400% zoom needs a person to check.
- Content scanners can’t reach. Menus, pop-ups, pages behind a login, and the PDFs and Word documents linked from your site are often not scanned at all.
- Captions and transcripts. A tool can detect that a video has captions. It can’t tell whether they are accurate.
This is why a clean scan result is not the same as an accessible website. Use scanners for quick wins, then test the things only a person can judge.
A sensible way to use them
- Run an automated scan first, it’s free and fast, and it’ll catch the easy, obvious wins.
- Fix what it finds.
- Then do a real keyboard-only pass yourself: see our guide to testing with just a keyboard for exactly how.
- For anything customer-facing or high-stakes, bring in a human review on top. That’s the only way to catch what a scanner structurally can’t.
Free tools find only some of the problems. A manual accessibility audit finds the rest.
Not ready for a full audit? Send us your web address and we will tell you the three biggest barriers on your homepage, free.
Want the human layer done properly?
A full WCAG audit combines the same automated checks with genuine manual testing (keyboard, screen reader, and real-world usability) and gives you a prioritised, plain-English report.