# What is Ace by DAISY?

Source: https://epubcc.com/glossary/ace-by-daisy/ (updated 2026-11-04)

Ace by DAISY is a free accessibility checker for EPUB from the DAISY Consortium, available as a command-line tool and a desktop app. It helps evaluate an EPUB against accessibility practice; it does not replace a human review.

## Why it matters when you convert a PDF to EPUB

EPUBCheck tells you whether an EPUB is valid; Ace tells you about accessibility: missing accessibility metadata, images without alt text, headings out of order, page lists that the metadata promises but the book does not have. Running both is the usual check before publishing an EPUB.

Under the hood most of its checks of the HTML come from the axe engine (a DAISY fork with EPUB-specific rules), plus Ace's own checks of the package metadata. It runs on Node.js; version 1.4.6 was current on 2026-11-04.

How EpubCC handles it: Ace is not run on conversions. An EpubCC book lacks accessibility metadata, which Ace reports, and its images have empty alt text, which Ace accepts as decorative, so deciding which images need a description is still a job for a person.

**Is Ace by DAISY free?** Yes. It is an open-source project of the DAISY Consortium, installed with npm as @daisy/ace or as the Ace App for desktop.