Validation is the process of checking a publication for deviations from the requirements of the EPUB standards and WCAG accessibility guidelines. Some of the testing can be automated to speed up the process, but other tests can only be reliably carried out by a human. For example, a machine can detect whether an image has alternative text, but only a human can verify if the text is sufficiently meaningful.

Although deciphering validation messages can sometimes be complex, the process of finding and fixing errors is essential to perform. It ensures not just that a publication is accessible for persons with disabilities, but that the publication will render as expected for any readers. Skipping this step can lead to EPUB publications that are completely unusable.

To fully check a publication, the following validation sequence needs to be run:

  1. EPUBCheck — Validating the publication using EPUBCheck ensures that it conforms to the requirements of the EPUB standard.
  2. Ace by DAISY — Validating the publication using the Ace tool helps discover accessibility issues that can be tested automatically.
  3. Ace SMART — Manually checking the publication using the SMART tool ensure that it meets all the requirements of WCAG, thereby allowing a conformance claim to be made.

These steps can be followed for both EPUB 3 and EPUB 2 publications, although the Ace and SMART tools are not specifically optimized for checking EPUB 2. Refer to each tool's knowledge base page for more information.


This process is expected to be simplified in the future as efforts are made to integrate the three steps into a single application.

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