Accessibility - EPUB 3 Resources and Guidance
There is a range of guidance available for creating Accessible EPUB files - some high level and some more technical.
See idpf.org for comprehensive guidance on creating accessible EPUB files: http://www.idpf.org/accessibility/guidelines/
The EPUB 3 Resources and Guidance and EPUB Tools and Solution Gallery. provide a directory of EPUB tools and resources for all areas of the industry. Use the search functions to find the perfect solution for you or submit your own tool for listing within the gallery.
The epubcheck tool is the gold standard as far as EPUB 3 validation goes. epubcheck is currently hosted on a github project under the same name. The latest stable build is typically linked to from the main page, but can also be found by clicking on the Downloads tab. An online version of the tools is available here.
The new website epubtest.org has been launched in a collaboration between BISG, DAISY Consortium and the IDPF to provide a unified home for the definitive EPUB 3 Reading System Conformance Testsuite.