Kindle File Format is a proprietary e-book file format created by

Amazon.com Amazon.com, Inc. ( ) is an American multinational technology company focusing on e-commerce, cloud computing, online advertising, digital streaming, and artificial intelligence. It has been referred to as "one of the most influential economi ...

that can be downloaded and read on devices like

smartphones A smartphone is a portable computer device that combines mobile telephone and computing functions into one unit. They are distinguished from feature phones by their stronger hardware capabilities and extensive mobile operating systems, which ...

, tablets,

computers A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These prog ...

, or

e-reader An e-reader, also called an e-book reader or e-book device, is a mobile electronic device that is designed primarily for the purpose of reading digital e-books and periodicals. Any device that can display text on a screen may act as an e-read ...

s that have Amazon's Kindle app. E-book files in the Kindle File Format originally had the

filename extension A filename extension, file name extension or file extension is a suffix to the name of a computer file (e.g., .txt, .docx, .md). The extension indicates a characteristic of the file contents or its intended use. A filename extension is typically d ...

.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.

History

Kindle devices and apps are designed to use Amazon's e-book formats: AZW that is based on

Mobipocket Mobipocket SA was a French company incorporated in March 2000 that created the .mobi e-book file format and produced the Mobipocket Reader software for mobile phones, personal digital assistants (PDA) and desktop operating systems. The Mobipoc ...

; in fourth generation and later Kindles, AZW3, also called KF8; and in seventh generation and later Kindles, KFX. Kindles now support the

EPUB EPUB is an e-book file format that uses the ".epub" file extension. The term is short for ''electronic publication'' and is sometimes styled ''ePub''. EPUB is supported by many e-readers, and compatible software is available for most smartphones ...

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 format A proprietary file format is a file format of a company, organization, or individual that contains data that is ordered and stored according to a particular encoding-scheme, designed by the company or organization to be secret, such that the decodi ...

s. AZW files debuted with the first Amazon Kindle in 2007. Software such as the

free and open source Free and open-source software (FOSS) is a term used to refer to groups of software consisting of both free software and open-source software where anyone is freely licensed to use, copy, study, and change the software in any way, and the sour ...

Calibre In guns, particularly firearms, caliber (or calibre; sometimes abbreviated as "cal") is the specified nominal internal diameter of the gun barrel bore – regardless of how or where the bore is measured and whether the finished bore match ...

, Amazon's ''KindleGen'', 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 In computing, plain text is a loose term for data (e.g. file contents) that represent only characters of readable material but not its graphical representation nor other objects ( floating-point numbers, images, etc.). It may also include a lim ...

(TXT) and

Portable Document Format Portable Document Format (PDF), standardized as ISO 32000, is a file format developed by Adobe in 1992 to present documents, including text formatting and images, in a manner independent of application software, hardware, and operating systems ...

(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. AZW3 supports a subset of

HTML5 HTML5 is a markup language used for structuring and presenting content on the World Wide Web. It is the fifth and final major HTML version that is a World Wide Web Consortium (W3C) recommendation. The current specification is known as the HTML ...

and CSS3 features, while acting as a container for a backwards-compatible MOBI content document."Amazon Throws A Minor Curveball With HTML5-Powered Kindle Format 8"
TechCrunch, October 20, 2011. 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

hyphen The hyphen is a punctuation mark used to join words and to separate syllables of a single word. The use of hyphens is called hyphenation. ''Son-in-law'' is an example of a hyphenated word. The hyphen is sometimes confused with dashes ( figure ...

kerning In typography, kerning is the process of adjusting the spacing between characters in a proportional font, usually to achieve a visually pleasing result. Kerning adjusts the space between individual letterforms, while tracking (letter-spacin ...

and

ligatures Ligature may refer to: * Ligature (medicine), a piece of suture used to shut off a blood vessel or other anatomical structure ** Ligature (orthodontic), used in dentistry * Ligature (music), an element of musical notation used especially in the me ...

to the text; e-books that support this engine require the use of the "Kindle Format 10" (KFX) file format. 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. In 2022, while the Send-to-Kindle service only supported the original .mobi/.azw ebook formats (along with some other non-ebook file formats), Amazon announced removing this support in favor of

.epub EPUB is an e-book file format that uses the ".epub" file extension. The term is short for ''electronic publication'' and is sometimes styled ''ePub''. EPUB is supported by many e-readers, and compatible software is available for most smartphones ...

which will be converted to Amazon's KF8 (.azw3) from late-2022.

References

{{Ebooks Amazon (company) Computer file formats Electronic paper technology Ebooks