MOBI file format: what it is and how to use it
MOBI is the legacy Kindle format: Mobipocket's container that powered Amazon's early e-books before KFX and EPUB took over. Learn when to use it and what to choose instead.
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What is a MOBI file?
A .mobi file is an e-book in the Mobipocket format, the container Amazon bought in 2005 and built the early Kindle ecosystem on: HTML content packaged in a Palm-era database structure with Kindle metadata, optionally DRM-wrapped (.azw/.azw3 are its Amazon-grown descendants). It powered a decade of e-books, until Amazon deprecated it for sideloading in 2022 and embraced EPUB.
When should you use MOBI?
- Very old Kindles: first-generation devices and apps that predate EPUB support.
- Reading existing collections: libraries still hold large .mobi backlists.
- Understanding AZW variants: it is the ancestor of Amazon's proprietary formats.
When is another format a better fit?
For anything new, EPUB is the answer: Kindle's Send-to-Kindle converts it, and every other reader speaks it natively. For print-replica content PDF; for structured sources FB2. MOBI is a format you convert from now, not to.
The short version: MOBI is the retired Kindle container. Keep it working on old devices, and convert to EPUB for everything else.
How to open a MOBI file
On Windows
Double-click the file, or open it with Amazon Kindle (legacy).
On macOS
Calibre opens MOBI files on macOS.
In your browser
Open MOBI files right in a browser tab or with the dexrr viewer. No install, no upload.
Also opens in
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Amazon Kindle (legacy) -
Calibre -
FBReader
View or convert MOBI files
A quick preview or a new format. No install, no upload.
MOBI technical details
- Full name
- Mobipocket e-book
- Extensions
- .mobi .prc .azw
- MIME type
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application/x-mobipocket-ebook - Magic bytes
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42 4F 4F 4B 4D 4F 42 49 (BOOKMOBI, offset 60) - Compression
- Lossless or lossy
- Developer
- Mobipocket SA / Amazon
MOBI questions, answered
How do I open a .mobi file?
Calibre, older Kindle apps and FBReader open it; the current Kindle app no longer imports it. dexrr displays and converts mobi files directly in your browser.
Can I convert MOBI files online?
Yes, dexrr converts mobi locally in your browser: MOBI to EPUB for modern readers or MOBI to PDF for printing.
Is MOBI better than EPUB?
No, it is the older, weaker format Amazon itself deprecated. EPUB wins on features, openness and current support.
Why can't I email a .mobi to my Kindle anymore?
Amazon dropped MOBI sideloading in 2022. Send-to-Kindle now accepts EPUB and converts it to the modern format internally.
Is the MOBI format outdated?
Officially yes: deprecated by Amazon, kept alive only by old devices and existing library files.