What automated accessibility testing can and cannot catch

Automated testing is quick and consistent, but it covers only part of accessibility. Here is where it helps, where it stops and what to do next.

By Allie. Published and last reviewed October 16, 2026.

We built Allie on an automated engine, so we want to be plain about its limits. We will not quote a percentage, because the share of issues that tools find depends on how issues are counted and on the site. What is certain is that automated testing covers only part of accessibility.

What automated testing is good at

Rules that can be answered by inspecting code and computed styles are a good fit for software. Examples from the axe rule list include:

• Missing alternate text on images (image-alt).
• Text contrast that falls below the required ratio (color-contrast), in many cases.
• Form fields without a label (label).
• Links and buttons without a name (link-name, button-name).
• A missing page language or title (html-has-lang, document-title).
• Invalid or misused ARIA attributes and roles.

Software is also good at repeating the same check on every page and every release, which makes it useful for catching regressions.

What it cannot decide

• Whether alt text is meaningful. A tool can see that alt text exists, not whether “image123” or a good description is in it.
• Whether the reading and focus order make sense.
• Whether captions and transcripts are accurate.
• Whether a task can be completed with only a keyboard, a screen reader or voice control.
• Whether instructions and error messages are clear and whether content is understandable.
• Anything that needs a user to be logged in or to go through several steps, unless a test is set up to do it. A single-page scan sees the page as first loaded.

Deque's published rule list marks many rules with “needs review”, meaning the tool flags something a person must judge. Deque's own rule page says: “These are automated accessibility checks. Manual checks are also required.”

What the Department of Justice says

ADA.gov's web guidance says automated checkers and overlays can be helpful but need to be used carefully, like spelling or grammar checkers. It adds that a “clean” report does not necessarily mean everything is accessible, and that a report with a few errors does not necessarily mean there are accessibility barriers. It suggests pairing a manual check of a website with automated checkers.

A practical routine

1. Scan your key pages and fix what the tool finds.
2. Use your keyboard on the same pages: Tab through, check focus is always visible, open every menu and submit every form.
3. Zoom the page to 200 percent and check it still works, and view it at a narrow width.
4. Try a screen reader on your most important flow, such as checkout or contact.
5. Read your own content for link text, headings, error messages and captions.
6. Re-scan after changes and keep dated records of what you tested.
7. Ask real users who rely on assistive technology to try your key tasks, when you can.

Use the WCAG 2.2 checklist to plan the manual part, and read how Allie works on the methodology page.

What Allie does and does not claim

Allie tests one page against WCAG 2.2 A and AA rules using axe-core and tells you what failed and where. It does not certify conformance with WCAG or any law, and it does not replace a manual audit or legal advice.

Frequently asked questions

Can an automated tool tell me my site is accessible?

No. A tool can show failures it can detect. A page with no automated failures can still be hard to use. ADA.gov says a clean report does not necessarily mean everything is accessible.

What do I need besides an automated scan?

Manual checks with a keyboard, zoom and a screen reader, a review of your content, and, where possible, testing with people who use assistive technology.

Why not quote a percentage of issues found?

Published figures vary with how issues are counted and which sites are tested, so we do not quote one. We simply say that automated testing covers only part of accessibility.

Sources

We checked these pages when writing this guide.

• List of axe 4.10 rules, Deque University
• Guidance on Web Accessibility and the ADA, ADA.gov
• WCAG 2.2, W3C Recommendation

More guides

• WCAG 2.2 checklist
• Accessibility for nonprofits
• Accessibility barriers for small businesses
• Fixing common axe issues

This guide is general information, not legal advice, and Allie reports do not certify conformance with WCAG or any law.