Not sure if this is the correct place to post -- if not please move, sorry.
I realised that most people here probably use calibre and would have no problem fixing their EPUB to be cleanly processed by Amazon's Send to Kindle by themselves.
But I saw a lot of people on Reddit who asked about the EPUB encoding problem and have no idea how to use calibre, so I created this web tool to quickly add proper UTF-8 encoding declaration to the EPUB file. A few people so far have used them on reddit and liked them, so I decided maybe I should also post here as an alternative for less tech-savvy people.
The tool works by reading through .xhtml file in the EPUB, check if it has XML encoding declaration, and if not, just add the UTF-8 declaration. It's all done in the browser -- no data are uploaded to any servers.
Right now it only fixes the UTF-8 encoding problem, but if there are any other common errors in EPUB that cause send to kindle to failed, I may add them, too.
Note: UTF-8 is assumed. If the EPUB doesn't have encoding declaration, but is not in UTF-8, the tool will still mark them as UTF-8.
I believe the tool is capable enough to NOT destroy any EPUB file, but
no guarantee on that.
The Tool:
https://kindle-epub-fix.netlify.app/
GitHub :
https://github.com/innocenat/kindle-epub-fix