EPUB travels. Kindle formats are fussier.
EPUB is the format to keep if you want the widest choice of reading apps. Kindle formats are fussier. This site can often read MOBI or AZW3 that you are allowed to convert, and it cannot write those formats. Use Calibre on a computer when you must create them.
Comics are simpler. CBZ is a ZIP of images and is the practical copy. CBR is RAR, which we can unpack and cannot create. Do not convert books under DRM or books you do not have rights to convert.
If you already know the job, start with EPUB to MOBI or MOBI to EPUB.
Every format on the site is listed from the homepage.
DRM and comics
Open the tool that names your two formats and read what the download will contain before you delete the original. If a result does not match that description, tell us.
Chapter text, not a print replica
EPUB is the copy that opens in the widest set of reading apps. Kindle formats are fussier. This site can often read MOBI or AZW3 that you are allowed to convert, and it cannot write those formats. Create them in Calibre on a computer if you must. FB2 and EPUB can exchange chapter text. Fixed illustrated layouts are simplified.
DRM-locked books fail. Do not convert a book you are not allowed to convert. Comics are a different job. CBZ is pictures in a ZIP and is the practical copy. CBR is RAR, which can be unpacked and cannot be created here. Check the page order after you open the new archive. Keep the original ebook until the new file opens in the reader you actually use.
Open the new file in the reading app before you delete the old one. Chapter order and a missing image are easier to see in the app than in a file listing. Kindle formats you must create belong in Calibre. DRM is a lock, not a conversion problem this site will break. Comics should be checked page by page if the archive was large. If a chapter title is missing, the source file may have stored the title only as an image. The text tools cannot invent that title. Keep the original until the reading app shows every chapter you expect.
Read a chapter before you trust the file
Open the EPUB or FB2 in the reading app and check the first chapter, a middle chapter, and the last one. A missing image is obvious there and invisible in a file listing. If the book was a comic, check the page order the same way. CBZ should show pictures, not a single nested archive. DRM will fail with an error rather than a partial book. That error is the stop sign. Do not look for a workaround on this site.
Kindle files you must create still belong in Calibre or Kindle tools on a computer. Sending someone an EPUB when they asked for AZW3 is a different favor, and you should say which file you made. Keep the purchased file. The converted copy is for the reader app that could not open the original.
Library apps sometimes show a cover and still hide later chapters until you open them. Scroll the table of contents. If the last chapter title is missing, the conversion dropped it or the source never had it as text. Compare the chapter count with the original app before you remove the file you bought. A short sample chapter at the end of a book is normal for some stores. Do not confuse that sample with a failed conversion.