are errors normal in epubs?

[abe]

are these kind of errors normal with calibre ? almost all of my books have several types of errors. database isn't corrupted however


https://imgur.com/a/tRoeSMb

[DNSB]

Those errors are not normal. The first two relate to the dc:identifier element which is a required element and is not supposed to be blank or absent.

As for the third item, that looks like a Kobo epub which has structural issues.

The following snippet is the first 7 lines of the .opf file from a blank ePub3 generated by Sigil. The identifier, language, title and modified items MUST be present for an ePub3 file.

<?xml version="1.0" encoding="utf-8"?>
<package version="3.0" unique-identifier="BookId" xmlns="http://www.idpf.org/2007/opf">
<metadata xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:opf="http://www.idpf.org/2007/opf">
<dc:identifier id="BookId">urn:uuid:982c9231-abdd-4c4c-9ff5-d4814ae29041</dc:identifier>
<dc:language>en</dc:language>
<dc:title>[Main title here]</dc:title>
<meta property="dcterms:modified">2025-03-23T18:40:12Z</meta>

[KevinH]

No those errors are not normal in any spec epub. It looks like someone who does not know what they are doing, has edited the epub's OPF, removing the package tag unique id attribute or its target and improperly re-used an id.

This can be a sign that the epub was edited using poorly written software or that the epub itself was pirated by someone who feared the unique-id would somehow identify them so they removed it.

Either way, not normal.

[abe]

and is it problematic ? for me i mean, the user

it's weird because it never caused me issues, but now i've just updated the metadata for all books and created tag-based collections, and my device is much slower (i might make a separate post about it)

what's the quickest way to solve these errors, can i do a batch fix , or do i have to do it individually ?

[abe]

it seems my reply didnt work . you can see my response above

[KevinH]

Lack of a unique book id can cause some ebook organizing software to slow down because the book's unique id is often used alone or in combination with the modification date and time to uniquely identify a specific instance of the epub.

Also duplicate ids in an opf depending on where it is used in the opf can result in broken metadata or missing spine items, or lost manifest data.

You should probably fix those issues, little by little. Use the calibre editor to fix those issues or something like Sigil.

If you understand the form and function of an epub OPF you could fix things in the opf using simple text editor.

A batch script to add in the bookid metadata would be doable but if epub2, do not forget to update the unique identifier used in the ncx as well.

[JSWolf]

Originally Posted by KevinH

LA batch script to add in the bookid metadata would be doable but if epub2, do not forget to update the unique identifier used in the ncx as well.

It it's an ePub3 that you want to be backwards compatible with ePub2, then you'll want an NCX ToC that also has the ID.