Accessibility ≠ Overlay: an automated 100/100 does not mean WCAG conformance
A perfect score can be a useful signal, but it describes the checks run by that tool and how they are weighted. In Lighthouse, the accessibility score is a weighted average of its automated audits; manual audits do not affect that score.
Lighthouse itself states the limitation
Chrome documentation is clear: passing every automated audit and scoring 100 in accessibility does not guarantee that the audited page is accessible. Manual testing remains important. A 100/100 score therefore does not by itself mean WCAG conformance.
WCAG is not a score
WCAG defines conformance criteria, not an overall mark from 0 to 100. W3C states that no tool alone can determine whether a site meets accessibility standards; knowledgeable human evaluation is required.
What a 100 can hide
A page can pass automated checks and still have barriers requiring manual review: focus order, keyboard interaction, meaningful text alternatives, complex component behaviour or clear instructions. Coverage also depends on which pages, states and content were evaluated.
Tools remain extremely valuable
This does not reduce the value of Lighthouse, axe or other tools. They are excellent for finding issues quickly and repeatedly during development. axe-core says it automatically finds a portion of WCAG issues and returns “incomplete” cases when manual review is needed. The mistake is turning a score into a certification the tool was not designed to provide.
What does this have to do with overlays?
The same caution applies to claims of “automatic compliance”. Detecting, modifying or scoring what can be identified programmatically does not by itself demonstrate full website conformance. More automation can improve coverage, but it does not remove context, interaction or human judgement.
What about Blind Reader?
Blind Reader belongs on the user-assistance side. It can help a person access or work with content, but it does not turn a score into WCAG conformance, certify a website or replace evaluation. 100/100 means 100/100 for the checks that make up that score; it does not automatically mean “this website conforms to WCAG”.