Need help figuring out what's wrong with an ePub I generated

[Angius]

I noticed a lack of an ePub generation library for .NET and decided to make one. I thought that I was creating the final file properly, and Calibre was able to open and display it without any issues, but my Kindle won't read it, and the online ePub validators I tried just mostly hang without showing any useful errors.

I hope that perhaps someone more knowledgable about the format would be able to dissect what I generated and point me toward's what's wrong.

The generated ebook is attached to the post, and in case you don't trust random files downloaded from the internet, you can find the source code of the generator here and run the Demo project (requires .NET 8 SDK) to generate the exact same file I attached here.

[Karellen]

The epub is incomplete.
you have a single style in the css file being p
But the text in the html files have no p tags surrounding it. It is just raw text with no tags.

[PeterT]

Did you not see https://github.com/jonthysell/QuickEPUB ?

Additionally there is ePubCheck https://github.com/w3c/epubcheck?tab=readme-ov-file

[DNSB]

For what it is worth, I ran the epub through epubcheck and it came up with a list of 12 errors.
Some of them are trivial such as no <p></p> tags for text and the space before the first line in the ncx file.

Spoiler:

book.opf,N/A,N/A,Col: -1: ERROR(OPF-030): The unique-identifier ""BookId"" was not found.
book.opf,6,474,Col: 43: ERROR(OPF-054): Date value ""23.07.2024 23:09:36"" is not valid as per http://www.w3.org/TR/NOTE-datetime:Unexpected: ..
cover.jpg,N/A,N/A,Col: -1: ERROR(RSC-001): File ""cover.jpg"" could not be found.
chapter-1.html,10,256,"Col: 12: ERROR(RSC-005): Error while parsing file: element ""body"" incomplete; expected element ""address"", ""blockquote"", ""del"", ""div"", ""dl"", ""h1"", ""h2"", ""h3"", ""h4"", ""h5"", ""h6"", ""hr"", ""ins"", ""noscript"", ""ns:svg"", ""ol"", ""p"", ""pre"", ""script"", ""table"" or ""ul"" (with xmlns:ns=""http://www.w3.org/2000/svg"")"
chapter-2.html,10,252,"Col: 12: ERROR(RSC-005): Error while parsing file: element ""body"" incomplete; expected element ""address"", ""blockquote"", ""del"", ""div"", ""dl"", ""h1"", ""h2"", ""h3"", ""h4"", ""h5"", ""h6"", ""hr"", ""ins"", ""noscript"", ""ns:svg"", ""ol"", ""p"", ""pre"", ""script"", ""table"" or ""ul"" (with xmlns:ns=""http://www.w3.org/2000/svg"")"
chapter-3.html,10,251,"Col: 12: ERROR(RSC-005): Error while parsing file: element ""body"" incomplete; expected element ""address"", ""blockquote"", ""del"", ""div"", ""dl"", ""h1"", ""h2"", ""h3"", ""h4"", ""h5"", ""h6"", ""hr"", ""ins"", ""noscript"", ""ns:svg"", ""ol"", ""p"", ""pre"", ""script"", ""table"" or ""ul"" (with xmlns:ns=""http://www.w3.org/2000/svg"")"
book.opf,7,488,Col: 14: ERROR(RSC-005): Error while parsing file: element ""metadata"" incomplete; missing required elements ""dc:identifier"" and ""dc:language""
title.html,7,319,Col: 16: ERROR(RSC-005): Error while parsing file: element ""style"" missing required attribute ""type""
chapter-1.html,9,244,"Col: 17: ERROR(RSC-005): Error while parsing file: text not allowed here; expected element ""address"", ""blockquote"", ""del"", ""div"", ""dl"", ""h1"", ""h2"", ""h3"", ""h4"", ""h5"", ""h6"", ""hr"", ""ins"", ""noscript"", ""ns:svg"", ""ol"", ""p"", ""pre"", ""script"", ""table"" or ""ul"" (with xmlns:ns=""http://www.w3.org/2000/svg"")"
chapter-2.html,9,240,"Col: 14: ERROR(RSC-005): Error while parsing file: text not allowed here; expected element ""address"", ""blockquote"", ""del"", ""div"", ""dl"", ""h1"", ""h2"", ""h3"", ""h4"", ""h5"", ""h6"", ""hr"", ""ins"", ""noscript"", ""ns:svg"", ""ol"", ""p"", ""pre"", ""script"", ""table"" or ""ul"" (with xmlns:ns=""http://www.w3.org/2000/svg"")"
chapter-3.html,9,239,"Col: 19: ERROR(RSC-005): Error while parsing file: text not allowed here; expected element ""address"", ""blockquote"", ""del"", ""div"", ""dl"", ""h1"", ""h2"", ""h3"", ""h4"", ""h5"", ""h6"", ""hr"", ""ins"", ""noscript"", ""ns:svg"", ""ol"", ""p"", ""pre"", ""script"", ""table"" or ""ul"" (with xmlns:ns=""http://www.w3.org/2000/svg"")"
book.ncx,1,6,Col: 7: FATAL(RSC-016): Fatal Error while parsing file: The processing instruction target matching ""[xX][mM][lL]"" is not allowed.

Please note that calibre's viewer is very forgiving. Most dedicated renderers are not forgiving. If your ePub fails epubcheck, most publishers will bounce it back to you to be fixed.

[Angius]

Thanks for the answers! I did manage to fix my code, so it generates proper epubs now (at least according to EpubCheck)