What AZW3 to EPUB can read, and what it cannot write
Move a Kindle book you have the right to convert into a format other readers accept.
The tool extracts chapter text and builds an EPUB.
Kindle files and DRM
DRM-protected Kindle files will not convert. Illustrated fixed-layout books lose their design.
Why AZW3 to EPUB is its own job
AZW3 to EPUB sits on this site because AZW3 and EPUB are not interchangeable, even when they look similar in a file list. Move a Kindle book you have the right to convert into a format other readers accept. People convert AZW3 they own into EPUB so the book opens off the Kindle. EPUB is the copy to keep if you want the widest choice of reading apps. Kindle prefers its own formats.
The tool extracts chapter text and builds an EPUB.
The AZW3 file you already have
AZW3 is a Kindle format. Kindle reading apps understand it. Creating one needs Kindle tools or Calibre, not a browser. This site does not write a new AZW3.
Keep the Kindle file if you still read on Kindle.
What a EPUB result is for
The download has to be EPUB, because that is the format the next step named. EPUB is the copy to keep if you want the widest choice of reading apps. Kindle prefers its own formats. Chapter text you own can be repacked into EPUB or out of EPUB.
Pictures and precise page design will not match a print book.
How to tell that AZW3 to EPUB worked
AZW3 to EPUB is worth using only when EPUB is what the next step actually named. Move a Kindle book you have the right to convert into a format other readers accept. What you get from AZW3 to EPUB: The tool extracts chapter text and builds an EPUB. Before you trust it: DRM-protected Kindle files will not convert. Illustrated fixed-layout books lose their design. The file stays in your browser and is not uploaded. The limit is 100 MB. Keep the original until the download has been opened in the program that will use it. A second pass rarely helps. If the first EPUB file is rejected, read the error from the program that rejected it. Another conversion of a bad result usually makes the file worse, not more compatible. When you are done, you should still have the AZW3 original and one EPUB download that you have opened. If those two are the same kind of failure, this was the wrong tool and the page above is the place that says so. Convert only a book you own and are allowed to convert. AZW3 to EPUB moves chapter text. A fixed illustrated layout is simplified, and DRM-locked files fail. Kindle formats can often be read here and not written. Keep the original ebook until the new file opens in the reader you actually use.
Here is the decision for AZW3 to EPUB. You start with AZW3 and you stop when a real program accepts EPUB. Reading the text out of a file you are allowed to convert is the useful direction. A fixed, illustrated layout is simplified. DRM-locked books fail. If those two sentences describe a tradeoff you do not want, do not convert. Renaming the extension by hand will not do this job. Running the tool twice on its own output will not do it either.
DRM-protected Kindle files will not convert. Illustrated fixed-layout books lose their design.
A related step, if you still need one, is EPUB to AZW3.
Other jobs start from the homepage, where each tool is named for the conversion it actually does.