Free A11y Tools Tested on 5 Real Sites

I'll be honest with you: I went into this little experiment fully expecting to confirm what I already believed. I thought all these tools would basically tell me the same thing in slightly different fonts, and I'd wrap this up in an afternoon.

Reader, I was wrong. Embarrassingly wrong. Let me walk you through what happened.

The Setup

I picked five websites that represented a realistic cross-section of the web. A small restaurant with a static site, a mid-size e-commerce shop, a municipal government page, a nonprofit's donation portal, and a personal portfolio. I ran each through a free browser-based accessibility checker, an open-source accessibility engine (the free browser extension), the browser's built-in audit tool, and SCOUTb2, and I took notes. Lots of notes. My desk looked like a conspiracy board by the end.

The goal wasn't to "win" for any particular tool. I just genuinely wanted to know: if you're a freelancer, a solo developer, or a curious human being who cares about accessibility, what does each of these tools actually tell you for free?

The Nonprofit's Accessibility Checker: The Visual Storyteller

I have a soft spot for this checker. It's been around forever (an accessibility research nonprofit launched it in 2001, which means it's old enough to vote and buy beer), and the visual overlay approach is genuinely clever. You load a page, hit the extension, and suddenly the page is covered in little icons showing you where errors and warnings live, right in context.

On the restaurant site, the accessibility checker found 14 accessibility errors: missing image alt text, empty form labels, and some low-contrast text. On the government page, it flagged 38 issues, which honestly felt about right for a government page.

But here's where it gets interesting. The checker found zero SEO issues because it doesn't check SEO. It found zero performance data because it doesn't check performance. It found no broken links, no security headers, no Core Web Vitals. It does one thing, and it does that thing well, but it is a single instrument in what needs to be a full orchestra.

On the e-commerce site, the checker flagged missing form labels on the checkout page. That's real and that matters. But it said nothing about the fact that the page had a Largest Contentful Paint of 6.4 seconds, which is also real and also matters, just in a different discipline.

The Open-Source Accessibility Engine: The Developer's Best Friend

The engine (the free version, built into browser DevTools or available as its own extension) is the tool I'd hand to a developer over a designer. It lives in the DevTools panel, it speaks in code-level specifics, and it's excellent at what it does.

On the nonprofit donation portal, the engine found 11 violations that the accessibility checker had also caught, plus 3 that the checker missed: an ARIA attribute used incorrectly, a focus management issue in their donation modal, and a landmark region problem. Those are meaningful catches.

The engine is powered by a leading accessibility consultancy's rules engine, which is genuinely respected. The free version tests for around 80 rules automatically, and the issue descriptions are detailed enough that a developer can act on them immediately without searching for clarification.

The limitation is the same as the accessibility checker's: accessibility only. No SEO, no performance, no broken links. It's also clearly built for developers rather than for someone who just wants to understand why their site might be failing users. If you hand the engine to a non-technical client, they will stare at it like it owes them money.

The Browser's Built-In Auditor: The Performance Giant with Accessibility Side Quests

The built-in auditor is part of browser DevTools and it is genuinely impressive for performance analysis. Core Web Vitals, time to interactive, cumulative layout shift: the built-in auditor gives you real numbers with real context.

But here's something that surprised me when I actually dug into the numbers. The built-in auditor's accessibility audit covers somewhere around 30 to 40 percent of WCAG issues. That's their own documentation talking, not me being unfair. It catches the automatable stuff and flags the rest as "additional items to manually review." Which is honest! But it means you're getting a partial picture.

On the personal portfolio site, the built-in auditor gave an accessibility score of 94. Sounds great. The accessibility checker and the engine each found 4 issues on that same page that the built-in auditor didn't flag at all, including a keyboard navigation trap in the contact form. A score of 94 with a keyboard trap hiding underneath it is a useful reminder that scores aren't the same as audits.

The built-in auditor is also single-page only by default. You run it on the URL you have open. For a five-page brochure site that's fine. For anything larger, you're doing a lot of tab management.

SEO coverage in the built-in auditor is basic: title tags, meta descriptions, mobile viewport, robots.txt. It's a starting point, not a comprehensive audit.

SCOUTb2: The One That Made Me Recalibrate

I'll tell you where my prior assumptions collapsed. I was running SCOUTb2 on the government page, mostly expecting it to echo what the accessibility checker and the engine had already told me. And it did echo most of those accessibility findings. But then it kept going.

It flagged 6 broken links (which I then manually verified: all 6 were genuinely broken). It flagged missing X-Frame-Options and Content-Security-Policy headers. It found 3 images larger than 500KB that had no lazy loading. It found a missing canonical tag and duplicate H1s. It surfaced the Core Web Vitals data. It caught 2 pages with no lang attribute. It identified 4 missing aria-labels that the accessibility checker had actually missed.

All of that from one scan. All free. No account needed to run the scan (you do need a free account to export reports, which seems fair).

The 25+ accessibility checks cover the major WCAG 2.1 categories: images, forms, headings, keyboard navigation, color contrast, ARIA, landmark regions, and more. It's not going to replace a full manual audit with a screen reader, but neither will any of the other tools on this list.

What SCOUTb2 does that none of the others do is run the browser rendering the actual DOM. You get what a real user sees, including content rendered by JavaScript, content behind login walls (since you're already logged in when you scan), and dynamic elements that a server-side crawler would miss entirely.

The Honest Scorecard

If I had to summarize what I found across all five sites:

The accessibility checker catches accessibility issues visually and contextually. Excellent for non-developers. Misses everything outside accessibility.

The accessibility engine is the most technically rigorous free accessibility tool. Built for developers. Misses everything outside accessibility.

The built-in auditor is the best free performance tool and gives you a useful (but partial) accessibility score. Misses SEO depth, broken links, security headers, i18n.

SCOUTb2 covers the most ground in a single pass: accessibility (25+ checks), Core Web Vitals, SEO, broken links, security headers, i18n, and screenshot capture. For single-page audits it's free. Multi-page scanning (up to 10,000 pages) is available with PRO.

I'm not going to tell you to delete the accessibility checker or the engine. They're good at what they do, and sometimes a specialist tool is exactly what you need. But if I had to pick one free tool for a general site health check, SCOUTb2 is the one I'd reach for first, because I'd rather triage everything in one pass before deciding which specialist to call in.

You can install it free and run it on your own site in about 90 seconds. If that sounds worthwhile, the pricing page has the full breakdown of what's free versus what's in PRO.

My conspiracy board is down now. The desk is clean. But I did not expect to spend a weekend rethinking my entire tool stack.

Note: Tool capabilities and pricing may change. Information reflects conditions at time of writing. All automated tools, including SCOUTb2, detect a subset of possible issues; they do not replace thorough manual testing with assistive technologies.

Disclaimer: This article is for informational purposes only and does not constitute legal, professional, or compliance advice. SCOUTb2 is an automated scanning tool that helps identify common issues but does not guarantee full compliance with any standard or regulation.