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MOBI

Mobipocket E-Book

MOBI (Mobipocket) is the original e-book format used by Amazon Kindle. Based on the PalmDOC format and developed by Mobipocket (acquired by Amazon in 2005), MOBI was Kindle's native format until Amazon introduced AZW3/KF8 and later began supporting EPUB. MOBI files are still common in e-book libraries, especially for older Kindle content and books distributed outside Amazon's store. Calibre, the universal e-book manager, handles MOBI natively.

What is MOBI?

MOBI is a derivative of the PalmDOC format, extended with proprietary Amazon features. It stores e-book content as compressed HTML with images and metadata in a binary container. MOBI supports basic formatting (bold, italic, headings), images, tables of contents, and DRM (Digital Rights Management). Amazon's proprietary variants include AZW (early Kindle DRM-protected MOBI), KF8/AZW3 (newer format with better CSS support), and AZW4 (PDF wrapper). The original MOBI format (without DRM) is open enough that Calibre, KindleGen, and many converters handle it. DRM-protected MOBI/AZW files are locked to specific devices or accounts.

MOBI pros and cons

Advantages

  • Native Kindle format — compatible with older Kindle devices and Kindle apps
  • Widely distributed as a DRM-free format by independent authors and publishers
  • Good support in Calibre for both reading and conversion
  • Smaller file sizes than EPUB for the same content
  • Supported by older Kindle hardware that doesn't support KF8/AZW3
  • Easy to obtain from Project Gutenberg and many DRM-free e-book stores

Limitations

  • Not natively supported on non-Kindle e-readers (Kobo, Nook, Apple Books)
  • Amazon stopped accepting MOBI uploads to KDP in 2022 (replaced by EPUB)
  • Inferior formatting support compared to EPUB and KF8/AZW3
  • Limited CSS support — complex layouts may not render correctly
  • No native browser support
  • DRM-protected MOBI files are tied to the purchase account
  • Being phased out by Amazon in favour of newer Kindle formats

When should you convert MOBI files?

Convert MOBI to EPUB to use on Kobo, Apple Books, Nook, or any non-Kindle e-reader — Calibre does this excellently: right-click the book → Convert Books → set output to EPUB. Convert EPUB or PDF to MOBI for older Kindle devices or personal Kindle libraries — Calibre converts from virtually any format to MOBI. Convert MOBI to PDF for printing or sharing as a fixed-layout document. Amazon's Send to Kindle service accepts EPUB since 2022 and converts to Kindle format automatically; you no longer need to convert to MOBI for Kindle.

All FormatDrop conversions run entirely in your browser — no file upload, no server processing. Your files stay on your device.

MOBI FAQ

Can I read MOBI files on a Kobo or other non-Kindle e-reader?
Not natively — MOBI is a Kindle-specific format. To read MOBI on Kobo, Nook, or Apple Books, convert to EPUB using Calibre: add the MOBI file to Calibre, right-click → Convert Books → set output format to EPUB. The conversion is usually high-quality for text-based books.
What is the difference between MOBI, AZW, AZW3, and KFX?
MOBI is the original Mobipocket format. AZW is Amazon's DRM-protected MOBI. AZW3 (also called KF8) is the newer format with better CSS and layout support, used on Kindle devices since 2011. KFX is Amazon's latest format with enhanced typography. For practical purposes: DRM-free e-books are usually MOBI or EPUB; Amazon-purchased Kindle books are usually AZW or AZW3 (locked by DRM).
How do I convert MOBI to EPUB?
Calibre (free, calibre-ebook.com): add the MOBI file → right-click → Convert Books → Convert individually → set Output format to EPUB → click OK. Pandoc: `pandoc input.mobi -o output.epub`. Online converters like Zamzar handle MOBI to EPUB without software installation. For DRM-protected MOBI (AZW) files, conversion requires removing the DRM first, which requires the KFX Input plugin and DeDRM tools in Calibre.
Does Amazon still use MOBI?
Amazon phased out MOBI for author uploads to Kindle Direct Publishing (KDP) in August 2022 — KDP now requires EPUB. For sending books to your personal Kindle via the Send to Kindle service, Amazon converts various formats automatically. Existing MOBI files in your Kindle library continue to work on older Kindle devices, and Kindle apps still read MOBI. However, MOBI is a legacy format being replaced by KF8/AZW3 and EPUB.

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