EPUB is a popular e-book file format that has been in use for more than a decade. These file formats contain a small website complete with all kinds media and other elements. There are many WYSIWYG editors that allow the users to create a document and save it as EPUB file. There are other applications which can be used to convert existing e-books (in other file formats) into the EPUB file format easily.
While there are so many software that can produce EPUB files, not many of them follow the standards set by the latest versions of EPUB format. This might result in your EPUB files being displayed incorrectly or with errors on a e-book reader screen.
There is an official tool called EPUBCheck which can be used to check errors inside a EPUB file. It is command line Java application which can analyze the EPUB files and display the errors on the computer screen. The basic usage format of EPUBCheck is : java -jar epubcheck.jar ebook.epub where “ebook.epub” is the file being examined.
For finding some of the advanced options for scanning an EPUB file, you can either check the official documentation or you can give the command: java -jar epubcheck.jar –help which shows you a list of all the available options and command line switches.
We decided to test this tool by downloading an EPUB file from Archive.org. When we checked the downloaded file using this tool, it showed a large number of errors in the file. For example, it found out that the e-book had no cover image. Not having a cover image for an e-book could be a problem when it is viewed in e-book readers like Kindle.
It also found many errors saying that a media type has no fallback content. This type of error usually occurs when a scanned image is placed without a fallback text content for that image.
You can download EPUBCheck from https://github.com/w3c/epubcheck.