Automated accessibility testing tools reliably catch a genuine but limited subset of accessibility issues — missing alt text, insufficient colour contrast, form inputs without labels, malformed heading hierarchy. Published figures generally put this at somewhere around a third of real-world issues, which sounds like a modest number until you consider what it actually buys: catching that third continuously, on every pull request, for close to no ongoing cost, rather than catching it once a year during an expensive manual audit.
Running an automated scanner in continuous integration, failing the build on new violations, converts accessibility from a periodic audit exercise into an ongoing discipline the same way automated testing did for functional correctness. It doesn't replace the manual review covered in the piece on accessibility procurement — the two-thirds of issues automated tools miss are exactly the ones requiring human judgement, like whether a screen reader experience of a complex interactive widget actually makes sense — but it prevents the easy third from accumulating silently between audits.
The trap that undermines these tools in practice is treating every flagged issue as equally urgent, which produces the same alert fatigue covered elsewhere on this site regarding security scanning and monitoring. A scanner reporting two hundred issues on first run, many of them low-impact or false positives specific to how the tool interprets a particular component, trains a team to ignore the report entirely rather than triaging it properly. Starting with a smaller, curated ruleset covering the highest-impact issues, and expanding it deliberately, produces a report that actually gets acted on.
Manual testing with an actual screen reader, on your own primary user journeys, remains irreplaceable and should happen on a schedule regardless of what automation catches. The two together — continuous automated scanning preventing regression, periodic manual testing catching what automation structurally cannot — is a considerably more realistic and sustainable accessibility programme than either alone.
