Every team shopping for accessibility tooling hits the same wall: dozens of products promise to make your site compliant, but no scanner can do that alone. Choosing well means understanding exactly where automation is strong, where it is blind, and how to fill the gap with human testing.
This guide cuts through the marketing. We will cover what the best accessibility checkers can and cannot detect, when free tools are enough versus when paid features earn their keep, the real difference between one-off scans and continuous monitoring, and how to build a workflow that combines automated and manual testing into something defensible.
What automated checkers actually catch
Automated tools parse your rendered DOM and apply rules. They are excellent at finding things with an unambiguous machine signature: an <img> with no alt attribute, a form <input> with no associated <label>, a button with no accessible name, a missing page <title>, duplicate id values, or text that fails the contrast thresholds of 4.5:1 for normal text and 3:1 for large text (at least 18pt, or 14pt bold) and UI components.
A large share of WCAG 2.2 criteria can only be confirmed by a person, because they depend on meaning and context that a rule engine cannot evaluate. So the central question when comparing the best accessibility checkers is not 'how many rules does it run' but 'how clearly does it separate confirmed failures from things a human must check'.
What automation cannot catch
A scanner can confirm that alt text exists; it cannot tell you whether alt="image123.jpg" describes the photo. It can confirm a heading is marked up as a heading, but not whether your heading order is logical. These judgment calls are where automation goes quiet:
- Whether alt text and link text are actually meaningful and describe their target
- Keyboard operability and a visible, logical focus order across interactive components
- Screen-reader output: does the announced experience match the visual one
- WCAG 2.2 additions like 2.5.8 Target Size Minimum (24x24 CSS px, AA), 2.4.11 Focus Not Obscured Minimum (AA), and 3.3.8 Accessible Authentication Minimum (AA), which usually need real interaction to verify
- Reading order, error recovery in forms, and whether motion and dragging movements have accessible alternatives
Treat any tool that markets '100% compliance' or an automatic overlay fix with suspicion. There is no automated path to WCAG 2.2 AA; the trade-off between automated and manual testing is something you manage, not eliminate.
Free vs paid: where the line really is
A capable free checker handles what most teams need first: run it, get a prioritized list of confirmed code-level defects, and fix them. AccessScan does this in the browser and also offers a free contrast checker and accessibility statement generator, which covers a lot of ground at zero cost. For a small site or an initial cleanup, free is genuinely sufficient.
Paid tiers earn their price on three things, not rule count: scale (crawling hundreds of URLs and authenticated pages behind a login), workflow (issue assignment, ticket export, history, and trend lines), and automation (CI integration plus scheduled monitoring). A one-page consultancy may never need these. A product that ships weekly recoups the cost the first time monitoring catches a regression before a customer does.
Scan vs monitoring
A scan is a snapshot. Monitoring is the same scan on a schedule with alerting on regressions. The distinction matters because accessibility is not a state you reach once - it decays. A designer tweaks a brand color and breaks contrast; a developer ships a new modal without a focus trap; a marketer publishes a CMS page with an unlabeled embedded form. None of these show up in a scan you ran last quarter.
Match the cadence to your release rhythm. A static brochure site is fine with a quarterly scan plus a re-scan after any redesign. A frequently updated app wants automated checks in the pull-request pipeline so a contrast or labeling regression fails the build, backed by a weekly full-site crawl that catches problems in content engineers never touch.
Combining automated and manual testing
The reliable pattern is a funnel. Automation does the wide, cheap first pass and removes the noise so humans spend their expensive time on judgment, not on hunting for missing alt attributes.
- Run an automated scan to clear all machine-detectable failures first
- Do a keyboard-only pass: tab through every interactive element and confirm focus is visible and the order is logical
- Run a screen reader (VoiceOver, NVDA, or JAWS) on key flows - checkout, signup, contact
- Spot-check the WCAG 2.2 judgment criteria automation skips, especially accessible authentication and target size
- Track everything against the accessibility checklist so coverage is documented, not remembered
This combination is also what regulators expect. The European Accessibility Act, which applies from 28 June 2025, points to WCAG 2.2 Level A and AA through EN 301 549 - a bar no scanner can clear by itself. A documented mix of automated and manual testing, plus a published accessibility statement, is what makes a conformance claim defensible.
A short checklist for choosing a tool
- Does it clearly separate confirmed failures from 'needs review' items, rather than inflating a single score?
- Does it map findings to specific WCAG 2.2 success criteria you can verify?
- Does it cover WCAG 2.2, not just 2.0 or 2.1, given the newer AA criteria?
- Can it crawl multiple and authenticated pages if your site needs that?
- Does it offer scheduled monitoring and CI integration if you ship often?
- Does it avoid overlay-style 'auto-fix' claims that no real tool can deliver?
- Is the free tier enough to start today and prove value before you pay?
Start by running a free scan now, fix what it confirms, then decide whether your release cadence justifies paid monitoring. The best accessibility checker is the one whose honest output you will actually act on - paired with the manual testing it can never replace.