What is the AZW3 file format?
An .azw3 file contains a digital publication saved in the proprietary Amazon Kindle Format 8 (KF8). .azw3 files support a wide array of formatting options for better device compatibility, based on HTML5 and CSS3. .azw3 also supports DRM features for copy-protected titles. The format is backward-compatible with .mobi format containers - a single .azw3 file can carry both a KF8 section and a legacy MOBI fallback, allowing older Kindle firmware to still read the content.
.azw3 files can be viewed on mobile devices and e-readers, as well as using PC or Mac applications. Compared to its predecessor, the .azw format, KF8 supports:
- Wider range of CSS styles,
- More font types including embedded custom fonts,
- More flexible page layout designs.
AZW3 was developed in 2011 as a successor to the older .azw format, which was used in Kindle devices since their debut in 2007. The Kindle Fire was the first device to use the .azw3 format, and all fourth-generation Kindle devices and PC/Mac applications support it. The format soon started to replace the MOBI format as the standard Kindle container.
Since 2015, .azw3 files have been gradually replaced by the .kfx format (Kindle Format 10), which brings further typographic refinements. Nevertheless, .azw3 remains widely distributed and is fully supported across current Kindle apps and devices, and can be converted to open formats like .epub using tools such as Calibre.
Security & safety
RISK: LOWAZW3 is e-book data and safe to read. The real friction is DRM, not malware: purchased Kindle books are account-locked, so generic apps refuse them and conversion is blocked - that's a rights restriction, not a virus. Removing DRM violates Amazon's terms and may be illegal in your jurisdiction. The practical risk is pirated-e-book download sites (bundled adware/fake downloads). Treat DRM-free files you create as ordinary documents.
Format details
in a nutshellPrograms that open AZW3 files
Windows3 apps
Calibre
Open-source Add the .azw3 to the library to read and convert it (EPUB/PDF/etc.). Works on DRM-free files; DRM books won't import without authorisation. 
Kindle for PC
Free Read AZW3 books delivered to your Amazon account; the official reader for purchased (DRM) Kindle books. 
macOS3 apps
Linux2 apps
Calibre
Open-source Primary option on Linux: add the .azw3, read in the built-in viewer, convert to EPUB/PDF. 
Android2 apps
Amazon Kindle (app)
Free Read Kindle books on your account; sideload DRM-free AZW3 via the app's import or the Documents folder.
Amazon Kindle (app)
Free Read account books; the iOS app no longer links to the Kindle Store (since 2022) but reads delivered books. Technical details
deep spec| Container structure | Palm Database (PDB) binary format; the same underlying container used by .mobi and .prc files, extended with KF8-specific records |
| File identification | 8-byte type+creator field "BOOKMOBI" at offset 60 in the PDB header; no fixed magic bytes exist at offset 0 |
| Internal markup | HTML5 and CSS3 content stored in compressed records within the Palm Database container |
| MIME type | application/vnd.amazon.ebook |
| DRM support | Amazon KFX/Topaz DRM (AES-based encryption) for purchased content; DRM-free variant used for sideloaded and Kindle Direct Publishing titles |
| Dual-section layout | A single file may contain both a KF8 section and a legacy MOBI section; a BOUNDARY record in the PDB separates them, enabling fallback on older Kindle firmware |
| Font embedding | Subsetted OTF and TTF custom fonts can be embedded; a capability absent from earlier .azw and MOBI formats |
| CSS capabilities | CSS3 subset including media queries, multi-column layout, advanced selectors, and explicit page-break controls |
| Supported image formats | JPEG, GIF, PNG, and BMP images stored as individual records within the PDB container |
| Metadata storage | EXTH header block inside the MOBI structure stores title, author, publisher, language, ISBN, ASIN, and cover thumbnail |
| Text compression | PalmDOC record-level zlib compression applied to text content records within the container |
| Character encoding | UTF-8 Unicode; KF8 mandated full Unicode support, replacing the CP1252/Latin-1 encoding used by earlier MOBI files |
| Navigation structure | NCX-style table of contents document for structured chapter navigation, a concept inherited from the EPUB/DAISY standard |
| Device compatibility | Kindle 4th-generation and later e-readers, Kindle Fire tablets, and Kindle apps for Windows, macOS, iOS, and Android |
| Successor format | .kfx (Kindle Format 10), introduced around 2015, supersedes .azw3 with improved typography and enhanced layout capabilities |
| Typical file size | Text-only novels generally range from 300 KB to 800 KB; illustrated or comic books can exceed 50 MB due to embedded images |
| Released | 2011 (Kindle Format 8 / KF8, introduced with the Kindle Fire) |
| Specification | kdp.amazon.com |
AZW3 conversions
Community Q&A
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