What is a .mobi file?
Mobipocket eBook · eBook · Mobipocket / Amazon · 2000
MOBI is an older eBook format that Amazon adopted for early Kindles. It holds reflowable text like EPUB but is now largely retired in favour of EPUB and Amazon's newer formats.
What is a .mobi file used for?
MOBI was one of the first widely used eBook formats and became the basis for Amazon's early Kindle books.
Amazon has since moved on to AZW3 and KFX, and now accepts EPUB directly, so MOBI is mostly a legacy format you meet in older libraries.
Calibre reads MOBI and converts it to and from EPUB with ease.
What opens a .mobi file?
The .mobi format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list.
Windows
- Calibre
- Kindle app
macOS
- Calibre
- Kindle app
Linux
- Calibre
- Foliate
Web
- Not common; convert first
Open a .mobi file step by step
- Confirm the file really is a .mobi. Drop it into the WhatFileType identifier, which reads its signature in your browser without uploading anything.
- On Windows, open it with Calibre or Kindle app.
- On Mac, use Calibre or Kindle app.
- On Linux, try Calibre or Foliate.
- Still stuck? Convert the .mobi to EPUB, which opens more widely.
Why can't I open my .mobi file?
Almost always because no installed app understands MOBI. Install one of the apps above, or convert the file to a format your existing software already reads. If double-clicking opens the wrong program instead of nothing at all, the file association is set to the wrong app rather than the file being broken.
The other possibility is that the file is not really a .mobi at all. Drop it into the file identifier to check it by its bytes instead of its name. Nothing is uploaded.
How to convert a .mobi file
You can convert a .mobi file to EPUB, PDF, AZW3.
Calibre converts MOBI to EPUB, which is the direction worth taking: MOBI is retired and EPUB is what current readers want. Books bought with DRM will not convert.
What is the .mobi file signature (magic bytes)?
A .mobi file carries the hex bytes 42 4F 4F 4B 4D 4F 42 49 at offset 60, which read as BOOKMOBI in ASCII. Programs identify MOBI by those bytes, not by the filename, so a renamed file still gives itself away.
These are the documented signatures for MOBI. For a full breakdown, see the Mobipocket file signature page.
| Hex signature | Offset | ASCII | Note |
|---|---|---|---|
| 42 4F 4F 4B 4D 4F 42 49 | 60 | BOOKMOBI | 'BOOKMOBI' at offset 60 |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .mobi file?
MOBI is an older eBook format that Amazon adopted for early Kindles. It holds reflowable text like EPUB but is now largely retired in favour of EPUB and Amazon's newer formats.
Is MOBI still supported?
Barely. Amazon has phased out MOBI in favour of EPUB and AZW3. Convert old MOBI files to EPUB with Calibre for future-proofing.
Comparisons
Related formats
Sources
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