Free Accessibility Checkers

Automated checks find only part of the problems

Every tool in this list says so in its own words. WebAIM writes on the WAVE help page that "WAVE cannot check all of the issues in these guidelines - no automated tool can", that the absence of errors does not mean a page is accessible or compliant, and that only a human can determine true accessibility. Deque's axe-core README states that the engine can find on average 57% of WCAG issues automatically and returns uncertain results as "incomplete" for manual review; Deque's product page puts the share at up to 80% with its tools, with manual testing still needed for the rest. WebAIM's overview of evaluation tools says tools "can only partially check accessibility through automation".

The scale of the problem is documented too. The WebAIM Million 2026 report found detectable WCAG 2 failures on 95.9% of the one million home pages it scanned, and notes that not all conformance failures can be detected automatically. So treat the tools below as a first pass that catches the obvious errors fast, and plan the manual checks in the routine further down.

Which tool for which job

The tools overlap, but each has a job it does best. From the official pages:

Some of these tools share rules. Pa11y can run with the axe runner instead of its default HTML_CodeSniffer, and Deque publishes the axe-core engine that its own extension builds on. Two checkers on the same engine mostly confirm the same findings, so pair one automated checker with a contrast tool and a screen reader instead of stacking checkers.

A check routine for a page

Work through the same five steps for every important page. Each one takes a few minutes and covers something the step before cannot.

1. Contrast. Check text and UI colors against the WCAG thresholds with the Colour Contrast Analyser or our color contrast checker. Large text and icons have lower thresholds than body text.
2. Headings. Run an extension or paste the page into the heading structure checker: one H1, no skipped levels, headings that describe the section. Screen reader users jump between headings, so the outline is the page's table of contents.
3. Alt text. WAVE shows every alternative text so a person can judge it, because the tool cannot decide if it is equivalent and appropriate. Our guide on how to write alt text covers decorative images, charts and product photos.
4. Keyboard. Put the mouse away and tab through the page. Every link, button and form field must be reachable, visibly focused and usable with Enter or Space. Check that tap targets are large enough with our touch target sizes guide.
5. Screen reader. Listen to the page once with NVDA on Windows or VoiceOver on a Mac. Silktide's extension includes a screen reader simulator for a first impression, but its own page recommends real screen readers such as NVDA, VoiceOver or TalkBack for proper testing.

Our WCAG accessibility basics guide explains the levels A, AA and AAA and the success criteria these checks map to.

What our tools cover

Four of our browser tools fit into the routine above and run without an account:

• The color contrast checker gives the ratio for a text and background pair and the AA and AAA results for normal and large text.
• The heading structure checker lists the H1 to H6 outline of a page and flags skipped levels.
• The readability checker scores how hard a text is to read, which matters for plain language and for users with cognitive disabilities.
• The HTML formatter makes markup readable, so missing labels, landmarks and alt attributes are easier to spot in the source.

None of them replaces a full checker or a screen reader. They are for the quick questions that come up while writing and designing, before the page goes through the full routine.

Checked and written by Tobias. Updated October 24, 2026.

Frequently asked questions