The EPUB Accessibility specification defines discoverability requirements and accessibility conformance for EPUB publications.


As EPUB is built on Open Web Platform technologies, like HTML and CSS, the EPUB Accessibility specification builds on the Web Content Accessibility Guidelines (WCAG) to define accessibility conformance for EPUB publications.

The primary advantage of this approach to accessibility is that it keeps EPUB aligned with the body of work that has already been done to make web content accessible. It also immediately makes web content accessibility specialists knowledgeable about the issues involved in ebook production. And, more generally, it means that content creators seeking to discover how to make their publications more accessible have a wealth of general resources available to them beyond this knowledge base.

But EPUB is also its own unique format, and WCAG is not a simple blanket set of practices that all apply in every situation. The knowledge base aims to bridge this gap for EPUB content by focusing on how to make rich publications that adhere to WCAG. Unlike the general web, where each site's design often brings its own unique issues, books are more often composed of the same sets of building blocks, making accessibility mappings useful to a broad range of publishers.


The EPUB Accessibility specification defines three key areas for conformance:

1. Discoverability

The discovery section of the specification identifies accessibility metadata that has to be included in the EPUB package document.

It is required that all publications include the following:

  • A summary describing their accessibility in human-readable language.
  • A list of all accessibility features.
  • The modes in which the content is expressed (e.g., textual, visual).
  • Any potential physical hazards the content might present (e.g., risk of seizure).

A more complete overview of this metadata is provided in the Metadata section of this knowledge base.

The inculsion of this metadata allows EPUB publications to be self-descriptive about their accessibility conformance, or lack thereof.

2. Accesibility

The accessibility section of the specification describes content conformance requirements. These requirements break down into two sections:

WCAG Conformance

EPUB publications must meet WCAG Level A or AA in order to conform to the specification, with AA being the recommended conformance level.

EPUB-specific Conformance

The specification defines two conformance criteria that are currently specific to EPUB: page navigation and synchronized media playback.

3. Optimizations

A third section of the specification deals with "optimized publications". These are publications that do not meet the WCAG definition of being widely accessible but that are optimized for users with very specific needs. An example of this type of publication is an audio book. Audio books are accessible for persons who are blind, for example, but not for the deaf. Optimized publications are expected to conform to a standard for their target audience, but the accessibility specification does not specify these standards (i.e., this conformance is outside the scope of the specification).


The accessibility specification defines the following reporting metadata for EPUB publications:

A complete listing of this metadata and how to use it is provided in the Evaluation Metadata section of this knowledge base.


The distribution section of the specification dives into issues in the distribution chain that can limit the accessiblity of a publication.

The most important of these issues is to not apply digital rights management schemes to a publication that limit access to the content. When this occurs, a perfectly accessible publication might no longer be readable at all if, for example, assistive technologies are prevented from reading out the text.

The other requirement is to provide accessibility metadata in whatever format a vendor uses to ingest the publication. It is common in trade publishing, for example, for ONIX records to be provided to distributors, which is also where they will harvest metadata about the publication. If the ONIX accessibility fields are not completed, users may lose the ability to search and discover the accessibility properties.


The EPUB Accessibility was published together with a set of advisory techniques that explain how to meet its requirements. The techniques do not delve into issues already covered by WCAG, but are primarily limited to explaining how to understand WCAG's requirements where they might be confusing when applied to EPUB publications.

Frequently Asked Questions

What tools are available to check conformance?

The DAISY Consortium maintains two tools to help check conformance of EPUB publications:


The Ace tool provides automated checking and reporting on a number of WCAG requirements. Passing the Ace validation tool is not sufficient to claim conformance to the specification, however, as not all WCAG requirements can be checked by machine.

The SMART tool is a complement to the Ace tool that helps evaluators walk through all of the manual checks needed to ensure conformance to the accessibility specification.