AZW File (.azw): What It Is, How It Works + Sample Files

The basics

What is an AZW file?

AZW is the format of the e-books Amazon sold for the first Kindles from 2007. Amazon had bought Mobipocket in 2005, and AZW was its MOBI format with an Amazon extension, Amazon's DRM and, usually, stronger compression. A DRM-free AZW is simply a MOBI file: rename it to .mobi and MOBI readers open it.

Two other things go by the name AZW, which explains a lot of confusion:

Kindle books in general. "AZW" is used loosely for any Kindle Store book, whatever format is actually inside.
A family of extensions. AZW1 (Topaz), AZW3 (KF8), AZW4 (a PDF-like format for textbooks) and AZW8 (KFX) are different formats that share the prefix. They are not newer versions of AZW in the way the numbers suggest.

To tell an AZW from the rest, look at the inside: BOOKMOBI at byte 60 and file version 6 in the MOBI header mean classic AZW (KF7); file version 8 means KF8.

Anatomy

What's inside an AZW file

A DRM-free AZW file has exactly the structure of a MOBI file, and our sample-book.azw is one. Here it is taken apart, with the fields that are different in a book bought from the Kindle Store pointed out.

sample-book.azw (header, record 0, records)

sample-book.azw: 123,159 bytes, 11 records

Palm database header
00000000  41 5F 53 6D 61 6C 6C 5F …   A_Small_Guide_to_Paper_Boats
0000003C  42 4F 4F 4B 4D 4F 42 49     BOOKMOBI
0000004C  00 0B                       11 records

Record 0
000000A8  00 02 00 00 00 00 0F 83 00 01 10 00 00 00 00 00
          │           │           │     │     └ encryption: 0, none
          │           │           │     └ text record size: 4,096
          │           │           └ 1 text record
          │           └ 3,971 bytes of text
          └ compression: 2, PalmDOC
000000B8  4D 4F 42 49 00 00 00 E8 00 00 00 02 00 00 FD E9
          MOBI, header 232 bytes, type 2 (book), UTF-8
000000C8  E2 20 26 0B 00 00 00 06 …
          unique ID, file version 6
          EXTH: 22 records, including
            100 author        Ada Example
            113 asin          (a Calibre ID here; an ASIN in store books)
            501 cdetype       EBOK
            524 language      en

rec  1        the text, PalmDOC-compressed HTML
rec  2-4      INDX, INDX, CNCX: table of contents
rec  5-7      JPEG images: cover, thumbnail, diagram
rec  8-9      FLIS, FCIS
rec 10        E9 8E 0D 0A  end of file

142 4F 4F 4B 4D 4F 42 49
BOOKMOBI
The Palm database type and creator at bytes 60 to 67, the same as in MOBI and AZW3 files. Nothing in the file says "AZW": only the extension does.
200 02
Compression
2 is PalmDOC compression. MobileRead describes the original AZW as MOBI with the high compression option, which this field records as 17480, HUFF/CDIC.
300 00
The encryption field
0 here, so any MOBI reader can open the file. In a protected book this field is non-zero and the text records are encrypted. This is the one value that decides whether an AZW opens outside Amazon's apps.
44D 4F 42 49
The MOBI header
The same header as any MOBI 6 book: length, book type, text encoding, a unique ID and file version 6.
5113 asin
The ASIN record
Named after the Amazon Standard Identification Number, Amazon's product number, which books from the Kindle Store carry here. Calibre fills it with its own book ID.
6501 cdetype
The document type
EBOK marks a book; other values include PDOC for a personal document.
7rec 5-7
Images
Each image is its own record. The text refers to them by number.

Variants

AZW, AZW3, KFX and the other Kindle formats

Name	What it is
AZW (KF7)	A MOBI book with Amazon's extension and usually its DRM. Amazon's first Kindle format.
`.mobi`, `.prc`	The same format from Mobipocket and other tools, normally without DRM. See MOBI.
AZW1 / `.tpz`	Topaz, an older and separate Amazon format.
AZW3 (KF8)	Kindle Format 8, from 2011: HTML5 and CSS in the same container as MOBI. See AZW3.
AZW4	A PDF-like format for textbooks.
AZW8 / KFX	Amazon's newest format.

Files that come with an AZW

Kindles keep reading data in separate files next to a book: .mbp for bookmarks, highlights and notes on MOBI and AZW books, and .apnx to map locations to printed page numbers. Copy a book without them and it still opens, just without those extras.

Protection

DRM: why an AZW file won't open

Most AZW files you find on a computer came from Amazon and have DRM. The book's text records are encrypted, and the key is tied to a Kindle device or app registered to the Amazon account that bought it. The file's headers, title and author aren't encrypted, so a library or a file manager can show a book that no app outside Amazon's can open.

Read a protected AZW on a Kindle or in a Kindle app signed in to the account that bought it. Downloading the book again from your Amazon library is easier than moving the file.
Other apps can't open it. Calibre and other e-book tools check the encryption field and stop with an error. That's the DRM working, not a damaged file.
Removing DRM breaks the Kindle Store's terms and is illegal in many countries, even for books you bought. If you need a book outside Kindle, look for a DRM-free edition: some publishers and shops sell them.

An AZW with DRM is still a valid Palm database: it has BOOKMOBI at byte 60 and readable metadata. A tool that reports "not an e-book" or "corrupt" for one is reading the encrypted text as if it were plain.

Status

AZW and Kindle today

2011: Amazon introduces KF8 (later known by the .azw3 extension), replacing the old format for new devices.
2022: as EPUB support arrives, Amazon's help pages announce that from late 2022 you'll no longer be able to send MOBI (.azw, .mobi) files with Send to Kindle. The deadline slips.
November to 20 December 2023: Amazon winds down MOBI support in Send to Kindle, naming .mobi, .azw and .prc files, and ends it by 20 December 2023.

The change only concerns sending files: documents already in your Kindle library weren't affected. To add a DRM-free book of your own, send an EPUB instead.

Troubleshooting

Why won't my AZW file open or send?

Calibre says the book has DRM. It came from the Kindle Store. Read it in a Kindle app on the account that bought it.
Send to Kindle rejects it. The service no longer accepts .azw files. Convert a DRM-free AZW to EPUB with Calibre and send that.
It opens in Calibre but not in a MOBI-only reader. It may be a joint MOBI/KF8 or a KF8-only file with an .azw name. Check the file version in the MOBI header, or whether BOOKMOBI is there at all.
An app doesn't recognise the extension. Rename a DRM-free AZW to .mobi; nothing else needs to change.
Highlights and notes are missing after copying a book to another device. They live in the .mbp file next to it, not in the AZW itself.

How to

How to open and convert an AZW file

Protected books: read them on a Kindle or in a Kindle app on the account that bought them.
DRM-free files: Calibre's e-book viewer opens them on Windows, macOS and Linux; Amazon's Kindle Previewer opens them too.
Check the metadata: ebook-meta book.azw prints the title, author and other details, often even for protected books, whose metadata isn't encrypted.
Convert a DRM-free AZW: ebook-convert book.azw book.epub (or .azw3, .pdf) with Calibre. If a tool doesn't accept the .azw extension, rename the file to .mobi first.
Make one: there's no reason to. Make a MOBI or, better, an AZW3 or EPUB. Any DRM-free .azw is a MOBI file with a different name, which is how our samples were made.

Free downloads

Sample AZW files to download

Free, DRM-free sample AZW files for testing upload filters, file-type detection, metadata extraction and converters. Real AZW files from the Kindle Store carry Amazon's DRM and can't be shared, so these are what a DRM-free AZW is: Mobipocket files made with Calibre 7.6 and saved with the .azw extension. They hold "A Small Guide to Paper Boats" by the fictional Ada Example.

sample-book.azw · 120.3 KBDownload

Browsers can't show this kind of file in a page. Download it to open it in the app it belongs to.

What's inside sample-book.azw

Browsers can't display AZW, so there's no live preview here. Open sample-book.azw in Calibre (renaming it to .mobi works too) to read the book.

A classic AZW
File version 6 in the MOBI header and no KF8 part: the format of AZW books for the first Kindles, without the DRM.
No encryption
The encryption field in record 0 is 0. A Kindle Store copy of a book would have a non-zero value here.
Metadata
EXTH records for the title, the author Ada Example, publisher, language, EBOK document type and a description that names this page.
Contents
A cover, a contents page linking to three chapters, a folding diagram, a numbered list and a table.

All sample AZW files

DRM-free AZW (KF7)
sample-book.azw · 120.3 KB (123,159 bytes)
A three-chapter MOBI 6 book saved as .azw, with cover, contents page, image, list and table. It's the file taken apart in the anatomy above.
- Testing upload filters and apps that accept `.azw`
- Checking detection by content rather than extension
Download
DRM-free AZW with a KF8 part
sample-joint.azw · 134.4 KB (137,603 bytes)
The same book as MOBI 6 and KF8 in one file, the joint layout Amazon's KindleGen 2 introduced in 2011, saved as .azw.
- Testing readers that pick the KF8 part
- Checking detectors that report MOBI vs KF8
Download

Ways to test with them

Detection by content: both files start with BOOKMOBI at byte 60. A detector should report them as Mobipocket files whatever the extension; sample-joint.azw also has a KF8 part after record 10.
Extension filters: upload both to a service that claims to accept Kindle books and check .azw isn't rejected while .mobi passes, or the other way round.
DRM handling: the encryption field is 0, so a converter should open both. If yours reports DRM, it isn't reading the PalmDOC header correctly.
Metadata extraction: expect the title "A Small Guide to Paper Boats", the author Ada Example and a description mentioning 99helpers.com/file-types/azw.

Free to use for testing, teaching and demos, commercially or not, with no attribution needed. A link back to this page is always appreciated.

Put it online

Have an AZW file? Give it a link.

Drop a DRM-free AZW file on 99helpers and it gets its own link to share. Browsers can't display AZW files, so visitors download it and open it in an e-book app.

Put an AZW file online

Questions

AZW files, frequently asked

What is an AZW file?

An e-book in Amazon's original Kindle format. It's a Mobipocket (MOBI) file with an Amazon extension and usually Amazon's DRM.

How do I open an AZW file?

If it came from the Kindle Store, open it on a Kindle or in a Kindle app on the account that bought it. If it's DRM-free, Calibre opens it on any computer.

Why can't Calibre open my AZW file?

Because it has DRM. Calibre checks the file's encryption field and won't open or convert protected books.

What's the difference between AZW and AZW3?

AZW is the older format, a MOBI book (Kindle Format 7). AZW3 is Kindle Format 8, from 2011, with HTML5, CSS, embedded fonts and fixed layout. Both use the same container.

What's the difference between AZW and MOBI?

Without DRM, nothing but the extension: rename a DRM-free AZW to .mobi and it opens in MOBI readers. AZW files from Amazon usually have DRM, which MOBI files normally don't.

Can I send an AZW file with Send to Kindle?

No. Amazon stopped accepting MOBI files, including .azw, by 20 December 2023. Send an EPUB instead.

How do I convert AZW to EPUB or PDF?

For a DRM-free file, use Calibre: ebook-convert book.azw book.epub. Files with DRM can't be converted.

Related formats

Other file types explained

MOBI file AZW3 file EPUB file FB2 file PDF file All file types

Keep going

Host an AZW file

Put a DRM-free Kindle book online at its own address.

Share an AZW file

Send an AZW book as a link instead of an attachment.

Sources

Last reviewed 27 October 2026.