Common EPUB Validation Errors (And How to Fix Each One)

Converting a manuscript to EPUB often surfaces validation errors that look intimidating but usually have a quick, specific fix. Find your exact error below.

Missing or Invalid Attributes

element “img” missing required attribute “alt” Caused by images inserted without alt text — the fix takes two minutes in Word or a text editor.

attribute “vlink” not allowed here A legacy attribute Word inserts automatically on the body tag — invalid in EPUB’s stricter XHTML.

attribute “clear” not allowed here Another Word-inserted legacy attribute, this time on line breaks — same family of issue, same fix approach.

File Structure Errors

Filename contains spaces Not about your EPUB file itself, but the HTML files inside it — and why renaming instead of recreating can break your images.

Still Seeing an Error Not Listed Here?

Most EPUB validation errors trace back to the same root cause: Microsoft Word inserting legacy HTML attributes during its “Save As HTML” process that aren’t valid in EPUB’s stricter XHTML format. If you’re seeing an error that isn’t listed above, it’s very likely the same pattern — an attribute Word added automatically that needs to be stripped out in a plain text editor.