Kindle File Format

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Kindle File Format
Amazon logo.svg
Filename extension
.azw, .azw3, .kfx
Internet media type
Initial release2007
Latest release
11 August 2015
Type of formate-book file format
Extended fromHTML5, CSS3, MOBI
Open format?No

Kindle File Format is a proprietary e-book file format created by that can be downloaded and read on devices like smartphones, tablets, computers, or e-readers that have Amazon's Kindle app. E-book files in the Kindle File Format originally had the filename extension .azw; version 8 (KF8) introduced HTML5 & CSS3 features and have the .azw3 extension, and version 10 introduced a new typesetting and layout engine featuring hyphens, kerning, & ligatures and have the .kfx extension.


Kindle devices and apps are designed to use Amazon's e-book formats: AZW that is based on Mobipocket; in fourth generation and later Kindles, AZW3, also called KF8; and in seventh generation and later Kindles, KFX.[1] Kindles now support the EPUB file format used by many other e-book readers. Similar to EPUB, Amazon's file formats are intended for reflowable, richly formatted e-book content and support DRM restrictions, but unlike EPUB, they are proprietary formats. AZW files debuted with the first Amazon Kindle in 2007.

Software such as the free and open source Calibre, Amazon's KindleGen,[2][3] and the email based Send-to-Kindle service are available to convert e-books into supported Kindle file formats. Kindle devices can also display some generic document formats such as plain text (TXT) and Portable Document Format (PDF) files; however, reflowing is not supported for these file types.

In late 2011, the Kindle Fire introduced "Kindle Format 8" (KF8), also known as AZW3 file format.[4] AZW3 supports a subset of HTML5 and CSS3 features,[5] while acting as a container for a backwards-compatible MOBI content document.[6][7]

In August 2015, all the Kindle e-readers released within the previous two years were updated with a new typesetting and layout engine that adds hyphens, kerning and ligatures to the text; e-books that support this engine require the use of the "Kindle Format 10" (KFX) file format.[8] E-books that support the enhanced typesetting format are indicated in the e-book's description on its product page.

In 2017, Amazon released Kindle Create, a tool that can convert Microsoft Word files to Kindle file format.[9]

In 2022, while the Send-to-Kindle service only supported the original .mobi/.azw ebook formats (along with some other non-ebook file formats),[10] Amazon announced removing this support in favor of .epub which will be converted to Amazon's KF8 (.azw3) from late-2022.[11][12][10]


  1. ^ "AZW3 file - Zamzar - Free online file conversion".
  2. ^ "Kindle Publishing Programs". July 12, 2011. Archived from the original on August 15, 2011. Retrieved August 15, 2011. Now via Internet Archive.
  3. ^ "KindleGen". Retrieved February 7, 2019.
  4. ^ Kindle Format 8,, October 2011.
  5. ^ "List of supported HTML tags and CSS elements". Amazon. Retrieved 4 August 2012.
  6. ^ Sabrina Ricci (March 6, 2012). "The New Kindle Format (KF8)". Digital Pubbing. Retrieved September 29, 2018.
  7. ^ "Amazon Throws A Minor Curveball With HTML5-Powered Kindle Format 8", TechCrunch, October 20, 2011.
  8. ^ Kindle eBooks with Improved Typography Use New KFX File Format. Retrieved 11 August 2015
  9. ^ "Kindle Create: A New Ebook Conversion Tool". EpubSecrets. April 6, 2017.
  10. ^ a b "Learn About Sending Documents to Your Kindle Library". Amazon. Archived from the original on January 25, 2022. Retrieved 2022-05-04.
  11. ^ Michael Kozlowski (April 30, 2022). "The Amazon Kindle will support EPUB in late 2022". Good E-Reader. Retrieved May 7, 2022.
  12. ^ Michael Cavacini (2022-05-04). "Amazon Kindle Will Support EPUB Books, Abandoning MOBI Format". Retrieved 2022-05-04.