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Ebook format

MOBI converter

The .mobi extension belongs to Mobipocket, one of the earliest commercial ebook formats and the direct ancestor of Amazon's Kindle files. A .mobi book packs compressed HTML-style markup and images into a Palm database shell, a design inherited from the handheld organizers it originally targeted.

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Runs on your device

Drop MOBI files here

Batch files can each use a different output. Nothing uploads for local conversions.

Working inputs include camera RAW, browser-local audio/video, PDF, CBZ/CBR comics, office documents, ebooks, markup, 3D models, structured text, images, and archives.

Where MOBI comes from

French company Mobipocket SA launched the format in 2000 for PDAs and early smartphones, building on the PalmDOC container. Amazon bought Mobipocket in 2005 and used its technology as the foundation of the Kindle. Amazon then retired it in stages, and Send-to-Kindle stopped accepting .mobi documents in 2022.

How MOBI works

  • Stored inside a PalmDB container as a sequence of numbered records, with text records capped at 4,096 bytes.
  • Text is compressed with PalmDOC LZ77 or the dictionary-based HUFF/CDIC scheme.
  • Markup is a constrained HTML 3.2-era dialect; CSS support is minimal and embedded fonts are absent.
  • Metadata lives in EXTH records appended to the MOBI header.
  • Images sit in separate records and are referenced by record index rather than by filename.

When to use MOBI

  • Reading DRM-free books on any Kindle generation, including the very first
  • Maintaining legacy ebook collections assembled before 2011
  • Converting old Mobipocket purchases to EPUB or AZW3 for modern devices
  • Feeding vintage PDA and smartphone reading apps that predate modern formats

Strengths and limitations

Strengths

  • Opens on every Kindle ever sold plus a long tail of legacy readers
  • Compact files thanks to record-level compression
  • Single self-contained file with embedded images and metadata

Limitations

  • DRM-protected copies cannot be converted; only DRM-free files are usable outside the Kindle ecosystem
  • No embedded fonts and only rudimentary CSS, so modern typography is impossible
  • Amazon's Send-to-Kindle service dropped the format in 2022
  • No fixed-layout support, ruling out comics and heavily designed books

Compatibility

Every Kindle device and app ever shipped can open a DRM-free .mobi, as can Calibre and most desktop readers. Modern non-Amazon hardware such as Kobo generally ignores it, so the format survives mainly as a legacy input for conversion.

Title, author, description, ISBN, and publisher data are carried in EXTH header records, and most conversion tools read and rewrite them.

Convert MOBI to another format