.azw3 File Extension

What kind of file is an .azw3?

An .azw3 file is usually an Amazon Kindle Format 8 ebook, also called KF8. It uses the registered application/vnd.amazon.mobi8-ebook MIME type. KF8 supports richer HTML and CSS book layouts than the older MOBI format, including reflowable text, fixed-layout pages, embedded fonts, and SVG graphics.¹²

The extension alone does not prove that a file is readable. IANA records no magic number for this format, so software must inspect its internal structure instead of trusting a short signature. An otherwise valid book may also be encrypted or protected by Kindle DRM.¹

How do I open an .azw3 on my computer?

Use an ebook reader rather than a web browser:

• Windows, macOS, and Linux: calibre can view and manage unprotected AZW3 books.
• Kindle devices and apps: Amazon Kindle software is the format's intended reader, although transfer and DRM rules depend on how the book was acquired.
• Other devices: convert an unprotected copy to EPUB if your preferred reader does not support AZW3.

calibre lists AZW3 as both an input and output format. It can convert an unprotected book to EPUB, PDF, DOCX, and several other formats.³ calibre does not open DRM-protected books.⁴

Poly support for .azw3

Poly gives supported AZW3 ebooks a thumbnail, paginated preview, full-text search, page-level visual search, and agent reading. This makes a successfully processed book searchable by its title, filename, and content.

The preview presents fixed pages rather than a native Kindle reading experience. Adjustable fonts, themes, reflow controls, and Kindle-specific navigation are therefore not interactive. DRM-protected, damaged, or otherwise unreadable books remain safely stored and searchable by filename, but their contents cannot be previewed, indexed, or read by the agent.

History of .azw3

Amazon introduced Kindle Format 8 in 2011 as a successor to its older Mobipocket-based publishing format. KF8 expanded ebook design with substantially broader HTML and CSS support, while remaining a proprietary Amazon format.²⁵

IANA registered application/vnd.amazon.mobi8-ebook on July 1, 2016. The registration assigns .azw3 as the extension, names Amazon's Kindle application and calibre as compatible software, and records application/x-mobi8-ebook as a deprecated alias.¹

Working with .azw3 and alternatives

Choose the destination according to the reading workflow:

When conversion is permitted, inspect the table of contents, fonts, images, page breaks, footnotes, and right-to-left text afterward. KF8 and EPUB use different package models, while PDF freezes a flexible ebook into pages. Keep the original .azw3 alongside any converted copy because reader-specific behavior or metadata may not survive conversion.

For long-term access, an open EPUB derivative is often more portable. Keep AZW3 when a Kindle device or established library requires it, and use PDF when preserving a particular paginated appearance matters.