EPUB Accessibility Checker: ACE vs Pagina vs Manual Review

If your organization needs EPUB files that satisfy WCAG 2.2 AA, Section 508, or the European Accessibility Act, you need to validate them. Three tools dominate the workflow: ACE by DAISY, EPUBCheck, and Pagina EPUB Checker. Here's what each actually catches — and what it misses.

Why automated checking isn't enough

Automated EPUB checkers can flag structural issues — missing alt attributes, heading order violations, missing language declarations. But they cannot determine whether alt text is meaningful, whether reading order matches visual order, or whether a table's headers convey the right semantics. A passing automated check does not mean your EPUB is accessible — it means it cleared the machine-checkable rules.

ACE by DAISY (free, open source)

What it checks:

EPUB Accessibility 1.1 conformance claims in the OPF package
WCAG 2.x success criteria (A and AA) for HTML content
Missing alt attributes on images
Heading hierarchy
Language attributes (xml:lang, lang)
Color contrast (basic automated checks)
Form and table accessibility

Output: HTML report with pass/fail/warning per rule, screenshots of flagged content. Also exports JSON and EARL for pipeline integration.

How to run:

npm install -g @daisy/ace
ace --outdir ./ace-report your-book.epub

What it misses: Reading order issues not reflected in markup order, meaningful alt text quality, complex table semantics, logical structure beyond heading nesting.

EPUBCheck (free, W3C reference validator)

What it checks:

EPUB specification conformance (3.x and 2.x)
OPF, NCX/NAV, and spine integrity
Media type and resource reference errors
CSS and HTML validity errors that affect rendering

Not an accessibility checker — EPUBCheck validates structural and specification conformance, not WCAG. Run it first to ensure a valid EPUB, then run ACE for accessibility.

java -jar epubcheck.jar your-book.epub

Pagina EPUB Checker (browser-based)

Pagina offers a free online EPUB checker at accessibility-checker.pagina.gmbh. It combines EPUBCheck and ACE in a single drag-and-drop interface. No install required — useful for one-off checks or when you can't run Node.js locally.

Limitation: upload size is restricted on the free tier; large EPUBs may time out.

Section 508 and EAA requirements

For Section 508 (US federal agencies and contractors): EPUB files must conform to WCAG 2.0 AA as a minimum. ACE + manual screen-reader review (NVDA/JAWS on Windows, VoiceOver on Mac) is the standard workflow. ACE gives you the automated baseline; screen-reader testing catches the rest.

For the European Accessibility Act (EAA 2026): WCAG 2.2 AA is required for digital products and services. EPUB3 with proper semantic markup satisfies EAA requirements by design in ways that PDF cannot. Full EAA compliance guide →

What toolkit.bot outputs

All EPUBs generated by toolkit.bot target EPUB Accessibility 1.1 + WCAG 2.2 AA:

Proper semantic HTML5 structure (headings, lists, tables as <table> elements)
Language attributes on the <html> element
NAV document with proper landmarks
Alt text on extracted images
EPUB 3.x valid (passes EPUBCheck)

Run ACE on any toolkit.bot output — it should pass all automated rules. If you find a failure, report it and we'll fix it.

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