Scanning Engines

AllyProof uses three engines to maximize detection coverage while maintaining a zero false-positive baseline. Combined estimated coverage: ~70% of automatable WCAG issues.

Engine Pipeline

Page loaded in Playwright
  ├── Engine 1: axe-core         → "Confirmed violations" (zero false positives)
  ├── Engine 2: HTML_CodeSniffer → "Additional findings" (deduped against axe-core)
  └── Engine 3: APCA             → "WCAG 3.0 Preview" (informational contrast)

Engines 2 and 3 run concurrently after axe-core completes.

Engine 1: axe-core (Primary)

axe-core is the industry standard. It has a zero false-positive policy, meaning it stays silent rather than risk reporting something that isn't a real violation. This makes it the trusted baseline for all AllyProof scans.

Enabled experimental rules

• css-orientation-lock — WCAG 1.3.4 Orientation
• label-content-name-mismatch — WCAG 2.5.3 Label in Name
• p-as-heading — WCAG 1.3.1 Info and Relationships
• table-fake-caption — WCAG 1.3.1 Info and Relationships
• td-has-header — WCAG 1.3.1 Info and Relationships

Engine 2: HTML_CodeSniffer (Secondary)

HTML_CodeSniffer uses different detection algorithms than axe-core, catching issues that axe-core's strict policy causes it to skip. Results are deduplicated against axe-core by matching HTML snippets — if axe-core already found the issue, HTMLCS findings are discarded.

Only errors and warnings are included. Notices (informational items) are excluded as too verbose. Rule IDs are prefixed with htmlcs- for source identification.

Engine 3: APCA Contrast (Preview)

WCAG 3.0 replaces the WCAG 2.x contrast ratio formula with APCA (Advanced Perceptual Contrast Algorithm). APCA accounts for font size, weight, and perceptual uniformity, producing more accurate readability predictions.

APCA Lc thresholds

Coverage Comparison