The common method today to test an EPUB file is using EPUBCHECK a Java software package maintained by the IDPF.
EPUBCHECK is always up to date with the latest standard, however it's error messages are somewhat cryptic and hard to understand. Many times it repeats the same message or similar message many times. All these make it hard to understand and use it.
The image on the left, shows a common test results screen from EPUBCHECK.
(The image shows EPUBCHECK 3.01 however the validator now uses EPUBCHECK 4)
Helicon Books validator uses EPUBCHECK internally as one of the steps for validating the EPUB file. The results are first analyzed and displayed in an easier to read method.
Validation according to EPUBCHECK only makes sure there are no coding errors, it shows nothing about readability. There are many more tests added using Helicon Books vas experience in EPUB files.
Some of the tests are:
We keep on adding tests based on our growing experience with EPUB