The short answer
- MOBI is a proprietary binary eBook format that stores reflowable text, images, navigation, and metadata, but DRM and uneven reader support can restrict opening or conversion.
- For an unencrypted file, open MOBI with a Kindle device or app, or with software such as Calibre that supports unprotected MOBI. On Windows or macOS, install a compatible reader and use its Open or Add Books command. On a phone, use a compatible eBook-reading app and import the file. Support differs by reader, especially for newer KF8 features. A DRM-protected file may require the authorized account and application.
- Treat an unfamiliar MOBI as more than plain static text. The format can permit JavaScript and frames, and proprietary extensions may include forms, indexes, databases, SQL queries, and framesets. Use a trusted reader, keep it updated, and avoid bypassing DRM. A valid extension or internal signature identifies the format but does not establish that the content is trustworthy.
MOBI File: Identify, Open, Check, and Convert Mobipocket eBooks
Mobipocket SA introduced MOBI in 2000, and Amazon acquired the company in 2005. The compiled format derives from the PalmDOC/PRC container and uses material based on OeBPS/EPUB. Record 0 contains the MOBI header and may include EXTH metadata. Its complete compiled specification was never officially published.
For an unprotected MOBI, a compatible converter may create EPUB or another supported eBook format. Conversion is not necessarily reversible: original component filenames may be absent, and fonts, layout, or enhanced features can change across readers. Amazon KDP no longer accepts reflowable or fixed-layout MOBI; Amazon directs new or updated books to EPUB, DOCX, or KPF and recommends checking them with Kindle Previewer or KDP Online Previewer.
How to open it
For an unencrypted file, open MOBI with a Kindle device or app, or with software such as Calibre that supports unprotected MOBI. On Windows or macOS, install a compatible reader and use its Open or Add Books command. On a phone, use a compatible eBook-reading app and import the file. Support differs by reader, especially for newer KF8 features. A DRM-protected file may require the authorized account and application.
For an unencrypted file, open MOBI with a Kindle device or app, or with software such as Calibre that supports unprotected MOBI. On Windows or macOS, install a compatible reader and use its Open or Add Books command. On a phone, use a compatible eBook-reading app and import the file. Support differs by reader, especially for newer KF8 features. A DRM-protected file may require the authorized account and application.
For an unprotected MOBI, a compatible converter may create EPUB or another supported eBook format. Conversion is not necessarily reversible: original component filenames may be absent, and fonts, layout, or enhanced features can change across readers. Amazon KDP no longer accepts reflowable or fixed-layout MOBI; Amazon directs new or updated books to EPUB, DOCX, or KPF and recommends checking them with Kindle Previewer or KDP Online Previewer.
File safety
Treat an unfamiliar MOBI as more than plain static text. The format can permit JavaScript and frames, and proprietary extensions may include forms, indexes, databases, SQL queries, and framesets. Use a trusted reader, keep it updated, and avoid bypassing DRM. A valid extension or internal signature identifies the format but does not establish that the content is trustworthy.
An unknown sender, a name ending in two extensions, or contents that do not match the extension — check before you open it.
Converting it
For an unprotected MOBI, a compatible converter may create EPUB or another supported eBook format. Conversion is not necessarily reversible: original component filenames may be absent, and fonts, layout, or enhanced features can change across readers. Amazon KDP no longer accepts reflowable or fixed-layout MOBI; Amazon directs new or updated books to EPUB, DOCX, or KPF and recommends checking them with Kindle Previewer or KDP Online Previewer.
Convert a copy, never the original, then compare quality, metadata, and layout against what you started with.
Common questions
What is a MOBI eBook file used for?
A MOBI file is a compiled binary eBook designed mainly for reflowable reading. It can contain text, images, navigation information, and metadata, with optional compression, encryption, or DRM.
How do I open a MOBI file on Windows?
Use a Windows eBook reader that supports unprotected MOBI, such as Calibre, then choose its Open or Add Books command. DRM-protected files may open only through the authorized account and application.
How do I read a MOBI file on a Mac?
Install a macOS reader that supports unprotected MOBI, import the file, and check its text and navigation. Rendering can differ because readers do not necessarily support every MOBI or KF8 feature.
How can I open a MOBI eBook on an Android phone?
Import it into an Android reading app that explicitly supports MOBI. If the app rejects the book, check for DRM or convert an unprotected copy to a format that the app supports.
Why will my MOBI file not open or show a DRM error?
The file may be encrypted or protected by DRM, unsupported by that reader, damaged, or mislabeled. Try the authorized reading application first and compare the file header with a recognized MOBI signature; conversion tools generally require an unprotected file.
Should I use MOBI or EPUB for a new eBook?
EPUB is the appropriate choice for new or updated Amazon submissions because KDP stopped accepting reflowable MOBI in 2021 and fixed-layout MOBI in 2025. MOBI remains relevant mainly for existing files and compatible legacy readers.
How do I convert a MOBI file to EPUB, and what can be lost?
Open an unprotected MOBI in a compatible converter and select EPUB as the output. Original component filenames cannot always be recovered, and fonts, layout, or enhanced features may change.
Is an unknown MOBI file safe to open?
Safety cannot be established from the extension alone. MOBI can permit JavaScript, frames, forms, and other extensions, so open unfamiliar files only in a trusted, updated reader and treat unexpected active content cautiously.
Does a BOOKMOBI or TEXtREAd signature prove a MOBI file is trustworthy?
No. Those byte sequences at absolute offset 60 can help identify the format, but a matching signature does not verify the book's source, content, integrity, or safety.
Can I convert a DRM-protected MOBI file with Calibre?
The cited preservation guidance describes Calibre and reverse-engineering tools as generally applicable to unprotected or unencrypted files. DRM can restrict opening, extraction, and conversion, so use the authorized service or application.
Related formats
Sources
Mobipocket File Format (FDD000472) · 美国国会图书馆（Library of Congress）格式描述文档
PRONOM PocketMobi (Palm Resource) File — Signatures, PUID fmt/396 · 英国国家档案馆 PRONOM 文件格式注册库签名分页
MOBI Support for eBooks Frequently Asked Questions · Amazon Kindle Direct Publishing 官方帮助中心
Mobipocket Format Preservation Assessment, Version 1.1 · 英国图书馆数字保存团队格式评估