Why Your Lighthouse Score of 100 Doesn't Mean You're Accessible
Google Lighthouse is built into Chrome DevTools and gives your site an accessibility score from 0 to 100. A score of 100 feels great. But it doesn't mean your site is accessible.
What Lighthouse actually checks
Lighthouse's accessibility audit runs a subset of axe-core rules - roughly 60 of axe-core's 84 rules. axe-core itself only covers about 30-40% of WCAG criteria that can be automated.
So Lighthouse checks a subset of a subset. A score of 100 means you passed ~60 automated checks. It says nothing about the hundreds of other accessibility requirements.
What Lighthouse misses
- Keyboard navigation - no tab order testing, no focus trap detection, no skip link verification
- Focus visibility - doesn't check if focused elements have visible indicators
- WCAG 2.2 criteria - Focus Not Obscured, Target Size, Accessible Authentication are all missing
- Alt text quality - checks existence, not whether 'IMG_0023.jpg' is actually descriptive
- Animation accessibility - no check for prefers-reduced-motion support
- ARIA live regions - no validation of dynamic content announcements
The real number
Automated tools reliably detect 30-40% of WCAG issues. Single-engine tools like Lighthouse detect even less. Multi-engine approaches push coverage closer to 50% by combining different rule sets and testing methodologies.
What to use instead
Lighthouse is a good starting point. But for genuine compliance:
- Run a multi-engine scanner (Lumi uses five engines)
- Integrate accessibility checks into your CI/CD pipeline
- Combine with periodic manual testing for the issues automation can't catch
