CONVERT
MOBI → TXTZ
Fast, secure MOBI to TXTZ conversion. No registration required.
DRAG. DROP. DONE.
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Max 100 MB · Free plan · No signup required
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Situation. MOBI is Amazon's legacy Mobipocket ebook format, the older Kindle delivery format. Solution: a TXTZ, produced below. Going from MOBI to TXTZ preserves the book structure — ToC, chapters, cover image, bold/italic runs, embedded fonts where licensing permits — and emits a TXTZ file that reflows correctly on small screens. The pipeline handles the CSS remapping and image re-encoding automatically. Worth knowing: MOBI is Amazon's legacy Mobipocket ebook format, the older Kindle delivery format. Meanwhile TXTZ is an ebook format tuned for reflowable reading on e-readers and mobile devices.
Mobipocket eBook
Source formatMOBI 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.
TXTZ eBook
Target formatTXTZ is a zipped plain text ebook format used by Calibre that packages a text file with optional metadata into a ZIP archive. It provides a lightweight ebook container when rich formatting is not required.
Why convert MOBI to TXTZ
Library applications (Calibre, Apple Books, Kindle library) prefer a single format for indexing. Converting mixed MOBI/TXTZ collections to one canonical TXTZ makes search, filter and sync work reliably.
HOW TO CONVERT
MOBI → TXTZ
Start the job
Upload a MOBI; we read metadata, cover image and table of contents from the source container.
Rewrite as TXTZ
The content is flowed into the TXTZ format with appropriate CSS, images re-encoded at recommended dimensions.
Save the ebook
Download the TXTZ. Side-load to your device or drop into your reader library.
Common Use Cases
Language-learning ebooks
Dictionary lookup and sentence highlighting work better on TXTZ in most reader apps than on MOBI.
Technical book reading
Code blocks and tables render more reliably in TXTZ across devices; MOBI can break them on narrow screens.
Audiobook companion
Whispersync-style features expect TXTZ; convert the MOBI of your book to pair text and audio.
Giveaways and mailing lists
Subscribers want a TXTZ they can open instantly; a MOBI introduces install friction that kills open rates.
MOBI vs TXTZ — Strengths and limitations
What each format does best, and where it falls short.
MOBI 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.
TXTZ Strengths
- Minimalist ebook wrapper.
- Plain-text core.
Limitations
- Niche.
- No reader adoption.
MOBI vs TXTZ — Technical specifications
Side-by-side comparison of the technical details.
| Specification | MOBI | TXTZ |
|---|---|---|
| MIME type | application/x-mobipocket-ebook | application/x-txtz |
| Extension | .mobi, .prc (PalmDOC variant) | .txtz |
| Container | Palm Database (PDB) | ZIP + TXT |
| Markup | Compressed HTML subset | — |
| Successor | .azw, .azw3 (Kindle-specific) | — |
| Tool | — | Calibre |
MOBI vs TXTZ — Typical file sizes
Approximate file sizes for common scenarios.
MOBI
- Text-only novel 200 KB - 1 MB
- Illustrated book 2-10 MB
TXTZ
- Novel (plain text) 200 KB - 1.5 MB
Quality & Compatibility
DRM-protected MOBI files cannot be converted — KaijuConverter respects publisher encryption and returns an error rather than stripping protection. Unprotected or self-published MOBI ebooks convert without restriction.
Tips for Best Results
- Use structure detection (TOC > chapters) to regenerate a clean table of contents in the TXTZ if the MOBI has none.
- Embedded fonts bloat file size — consider dropping them in Advanced if your reader uses its own typography anyway.
- For serialised fiction, keep cover art consistent across episodes by re-using one TXTZ cover rather than auto-generating per MOBI.
Frequently Asked Questions
Frequently Asked Questions
Yes. The free tier accepts files up to 100 MB without registration, email capture or watermarks. Paid plans raise the size cap, enable batch conversions and provide a REST API for automation, but nothing on the free tier is quality-limited — the output is exactly the same as on any paid plan.
Yes, provided the MOBI itself has a well-formed ToC. Calibre reads the navigation structure and writes an equivalent ToC into the TXTZ. If the source lacks a ToC we can generate one from heading levels in Advanced → structure detection.
Uploads run over HTTPS, files are processed in isolated containers, and both the source MOBI and the TXTZ output are auto-deleted within two hours. No account is required, file contents are never logged, and KaijuConverter does not use uploads for AI training. The paid plan adds a signable data-processing agreement for regulated workflows.
No. KaijuConverter does not strip digital rights management. DRM-free MOBI files — anything you authored yourself, public-domain classics, files from DRM-free retailers — convert without any restriction.
Most files finish in well under a minute. Small images and documents are typically ready in a few seconds; large video or audio files scale roughly with duration. Upload speed from your network is usually the dominant factor, not server time.
Yes. The cover is extracted from the MOBI and re-embedded in the TXTZ at device-appropriate dimensions. You can also override it in Advanced by uploading a custom cover image alongside the book file.
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Read guideSecure & Private Conversion
Your files are encrypted during transfer, processed in isolated containers, and automatically deleted within 60 minutes. We never read, share, or store your data.