Lighthouse Accessibility Score vs axe-core: What's the Difference?

How does Lighthouse calculate its accessibility score?

According to Chrome's documentation, the Lighthouse accessibility score is a weighted average of its accessibility audits. Each audit is pass or fail, and the weights are based on axe's user-impact assessments, so a failing high-impact audit costs more than a low-impact one. Manual audits and low-impact or best-practice audits do not affect the score.

Because each audit is simply pass or fail, one missing label and fifty missing labels cost the same. And because only automatable checks are scored, a page can score 100 while still being hard or impossible to use with a keyboard or screen reader.

What does axe-core report that a Lighthouse score hides?

axe-core returns four kinds of results for each rule: violations, passes, incomplete and inapplicable. Incomplete results are checks that ran but could not decide, such as text contrast over a background image, and they need a person to review them. A single pass/fail score cannot represent them.

Running axe-core directly also lets you choose rule sets, for example only the rules tagged for WCAG 2.2 Level AA, and see every affected element for each rule.

Why do Lighthouse, axe DevTools and AccessibilityScore.in give different results?

Even tools built on the same engine differ in what they run and how they count:

• Rule selection: Lighthouse runs a chosen set of axe checks as audits; other tools run more or fewer rules.
• Scoring: Lighthouse weights pass/fail audits by impact; AccessibilityScore.in starts at 100 and deducts 8, 4, 2 or 1 points for each failing critical, serious, moderate or minor rule.
• Extra rules: AccessibilityScore.in adds its own rules for visible focus, target size, accessible names, page language and page title.
• Page state: results depend on what has loaded, the viewport and whether a cookie banner or pop-up is open when the scan runs.
• Review items: AccessibilityScore.in lists axe's incomplete results as Needs review findings instead of dropping them.

When should you use Lighthouse, axe-core or AccessibilityScore.in?

Use each where it fits:

• Lighthouse: a quick check while developing in Chrome, alongside performance and SEO audits.
• axe-core directly, or axe DevTools: automated accessibility tests in your test suite or CI, with rules you choose.
• AccessibilityScore.in: a shareable report for a public page or a whole site of up to 250 pages, with CSV and PDF exports and scheduled re-scans.
• All of them: as a first pass before manual keyboard and screen reader testing, never instead of it.