.mobi

File format · Released 2000 · By Mobipocket SA

About MOBI Files

Mobipocket eBook

MOBI is the Mobipocket eBook format historically used by Amazon Kindle devices. While Amazon has moved to newer formats, MOBI remains relevant for older Kindles and legacy eBook libraries.

Family

eBooks

Extension

.mobi

MIME Type

application/x-mobipocket-ebook

Can Use As

Input Output

● Hex Magic-Bytes Signature (Offset 0x00) eBooks Binary/Text Stream

4D 4F 42 49 00 01 00 00 4B 41 49 4A ASCII: MOBI....KAIJ

Convert MOBI → PDF → 13+ CONVERSIONS ↓

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Lossless JPEG Q100 + standard COM segment padding for government & exam portals

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The story

HOW MOBI CAME TO BE.

2000

2005

2007

2022

MOBI was developed by Mobipocket, a French software company founded in 2000 by Thierry Brethes and Nathalie Ting. Their ebook reader ran on Palm devices, Pocket PCs, Symbian phones, and later BlackBerry. The format was a PalmDOC-based container using compressed HTML — elegantly simple for the hardware of its day.

Amazon bought Mobipocket in April 2005 and used MOBI as the direct ancestor of AZW when the first Kindle launched in November 2007. For a decade MOBI was the lingua franca of pre-Kindle ereaders. Amazon stopped accepting MOBI uploads to Kindle Direct Publishing in 2022 (EPUB is now preferred), effectively ending MOBI’s commercial life. Calibre and other tools still produce MOBI for legacy devices.

ISO / MIME SPECS

Technical Specifications

MIME type: application/x-mobipocket-ebook
Extension: .mobi, .prc (PalmDOC variant)
Container: Palm Database (PDB)
Markup: Compressed HTML subset
Successor: .azw, .azw3 (Kindle-specific)

Typical Sizes & Weights

Text-only novel

200 KB - 1 MB

Illustrated book

2-10 MB

STRENGTHS & LIMITATIONS.

Strengths

Universal Kindle support on every device ever released.
Very small file sizes for text-heavy books.
Mature tooling via Calibre and Amazon's KindleGen.
Simple container structure — easy to parse.

Limitations

Deprecated by Amazon for new uploads since 2022.
Poor support for rich typography (drop caps, ligatures, fixed layout).
No embedded fonts in the base format.
Proprietary container discouraged use outside Kindle.
Effectively a legacy format — new books go to AZW3/EPUB.

CURIOSITIES & TRIVIA.

Amazon's first Kindle (2007) ran MOBI files internally — AZW was just MOBI with added DRM.

Amazon bought Mobipocket in 2005 specifically to own the ebook format they would build the Kindle on.

A MOBI file uses Palm Database (PDB) containers — the same structure as Palm Pilot apps from the 1990s.

Every Kindle device reads MOBI out of the box, even if Amazon has stopped shipping it.

Kindle Direct Publishing stopped accepting MOBI uploads in August 2022 — EPUB is now the required submission format.

STUDIO TOOLS FOR MOBI

Specialized Utilities for .MOBI Files

View all 45 tools →

merge →

Merge PDF

Combine multiple PDF files into a single document. Drag and drop to reorder pages before merging. No software installation required.

split →

Split PDF

Split a PDF into separate files by page ranges or extract individual pages. Perfect for isolating chapters, invoices, or specific sections.

compress →

Compress PDF

Reduce PDF file size without visible quality loss. Choose from low, medium, or high compression levels. Ideal for email attachments and web uploads.

convert →

PDF to Word Converter

Convert PDF documents into editable Microsoft Word (DOCX) files online for free while preserving layout, tables, and typography.

convert →

Word to PDF Converter

Convert Microsoft Word documents (DOCX, DOC) into print-ready PDF files with exact font embedding and layout preservation.

convert →

PDF to Excel Converter

Extract tables, financial rows, and structured columns from PDF files directly into editable Microsoft Excel (XLSX) spreadsheets.

ocr →

Make PDF Searchable (OCR)

Add a searchable text layer to scanned PDF documents using OCR. The visual appearance stays the same but you can now search, select, and copy text.

decrypt →

Unlock PDF

Remove owner printing/copying restrictions and decrypt password-protected PDF files instantaneously once you enter the known password.

CONVERT FROM MOBI

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CONVERT TO MOBI

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Common Use Cases

Older Kindle devices, legacy eBook collections.