WAVE by WebAIM: How the Free Accessibility Checker Works

WAVE is the most widely used free web accessibility checker — a suite of tools from WebAIM, a non-profit at Utah State University, that shows exactly where your pages have accessibility problems for people with disabilities. Paste a URL into wave.webaim.org, or use the browser extension, and WAVE overlays icons for errors, contrast problems, alerts, and structure, all checked against WCAG. It is excellent and free — but by design it helps a human evaluate accessibility rather than declaring a site "compliant." Here is how to use it and what it can and cannot tell you.

How WAVE works

WAVE comes in three forms:

• Online tool — enter a URL at wave.webaim.org and it evaluates that single page. Free. It cannot reach password-protected, intranet, or local pages, and the page is sent to WAVE's servers for analysis.
• Browser extension — available for Chrome, Firefox, and Edge, it evaluates any page open in your browser, including logged-in, local, and dynamically generated content. It runs entirely on your machine, so nothing is sent to WAVE. Free.
• WAVE API — automated, remote evaluation for bulk or continuous testing, returning JSON or XML. This is the paid option, priced by credits.

What WAVE reports: six categories

Instead of a single pass-or-fail score, WAVE injects icons directly into the page and groups findings into six colored categories:

• Errors (red) — clear accessibility failures such as missing alt text, empty links or buttons, and missing form labels.
• Contrast Errors (blue) — text that fails color-contrast requirements.
• Alerts (yellow) — things that may be problems and need a human to judge.
• Features (green) — elements that likely help accessibility, surfaced so you can confirm they are used correctly.
• Structural Elements (purple) — headings, lists, and landmark regions.
• ARIA (pink) — ARIA roles and attributes in use.

A sidebar summarizes the counts and explains each item, mapping issues to WCAG (versions 2.1 and 2.2, primarily levels A and AA) and Section 508.

The most important thing WAVE tells you

WebAIM is refreshingly blunt about the limits of automation. In their own words, WAVE cannot tell you if your web content is accessible — only a human can — and the absence of errors does not mean your page is accessible or compliant. WAVE deliberately issues no badges or certifications.

This is a feature, not a flaw. Automated tools only catch a portion of accessibility issues. Estimates vary by study; Deque reports that its axe-core engine finds about 57 percent of WCAG problems. So rather than pretend, WAVE reveals things — such as the actual alt text on an image — and asks a human to judge whether they are appropriate, instead of auto-passing them.

Free, but single-page by design

The online tool and the extensions are free, but they evaluate one page at a time — they do not crawl an entire site. Whole-site or automated monitoring lives in the paid API, an enterprise engine, or WebAIM's separate human-evaluation services.

WAVE and axe-core

The other dominant engine in this space is axe-core by Deque, an open-source library embedded in many scanners and developer tools, including the accessibility audit in Chrome's Lighthouse. WAVE is visual, in-context, and oriented toward human evaluation; axe-core is a developer and CI engine that lives inside other products. Both are reputable, and many teams use both.

Where a whole-site scan fits

WAVE is perfect for reviewing a single important page in depth. But real sites have dozens or hundreds of pages. VitalSite runs an accessibility scan across your whole domain using the axe-core engine — the same class of tool — and folds the results into one report alongside security and AI visibility, with a fix guide for each issue. The same honesty applies to every automated tool, WAVE and VitalSite included: scanning catches the machine-detectable share, and final accessibility still needs human testing with real assistive technology. Use WAVE to go deep on a page, a whole-domain scan to find issues at scale, and human review to confirm.

→ Scan your whole site free with VitalSite