CONVERT
TXTZ → MOBI
Fast, secure TXTZ to MOBI conversion. No registration required.
DRAG. DROP. DONE.
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Max 100 MB · Free plan · No signup required
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TXTZ is an ebook format tuned for reflowable reading on e-readers and mobile devices. Reaching a MOBI from there is one hop. Going from TXTZ to MOBI preserves the book structure — ToC, chapters, cover image, bold/italic runs, embedded fonts where licensing permits — and emits a MOBI file that reflows correctly on small screens. The pipeline handles the CSS remapping and image re-encoding automatically. Technical note: TXTZ is an ebook format tuned for reflowable reading on e-readers and mobile devices. Compare that with MOBI is Amazon's legacy Mobipocket ebook format, the older Kindle delivery format.
TXTZ eBook
Source 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.
Mobipocket eBook
Target 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.
Why convert TXTZ to MOBI
Library applications (Calibre, Apple Books, Kindle library) prefer a single format for indexing. Converting mixed TXTZ/MOBI collections to one canonical MOBI makes search, filter and sync work reliably.
HOW TO CONVERT
TXTZ → MOBI
Start the job
Upload a TXTZ; we read metadata, cover image and table of contents from the source container.
Rewrite as MOBI
The content is flowed into the MOBI format with appropriate CSS, images re-encoded at recommended dimensions.
Save the ebook
Download the MOBI. 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 MOBI in most reader apps than on TXTZ.
Technical book reading
Code blocks and tables render more reliably in MOBI across devices; TXTZ can break them on narrow screens.
Audiobook companion
Whispersync-style features expect MOBI; convert the TXTZ of your book to pair text and audio.
Giveaways and mailing lists
Subscribers want a MOBI they can open instantly; a TXTZ introduces install friction that kills open rates.
TXTZ vs MOBI — Strengths and limitations
What each format does best, and where it falls short.
TXTZ Strengths
- Minimalist ebook wrapper.
- Plain-text core.
Limitations
- Niche.
- No reader adoption.
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 vs MOBI — Technical specifications
Side-by-side comparison of the technical details.
| Specification | TXTZ | MOBI |
|---|---|---|
| MIME type | application/x-txtz | application/x-mobipocket-ebook |
| Extension | .txtz | .mobi, .prc (PalmDOC variant) |
| Container | ZIP + TXT | Palm Database (PDB) |
| Tool | Calibre | — |
| Markup | — | Compressed HTML subset |
| Successor | — | .azw, .azw3 (Kindle-specific) |
TXTZ vs MOBI — Typical file sizes
Approximate file sizes for common scenarios.
TXTZ
- Novel (plain text) 200 KB - 1.5 MB
MOBI
- Text-only novel 200 KB - 1 MB
- Illustrated book 2-10 MB
Quality & Compatibility
DRM-protected TXTZ files cannot be converted — KaijuConverter respects publisher encryption and returns an error rather than stripping protection. Unprotected or self-published TXTZ ebooks convert without restriction.
Tips for Best Results
- Use structure detection (TOC > chapters) to regenerate a clean table of contents in the MOBI if the TXTZ 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 MOBI cover rather than auto-generating per TXTZ.
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 TXTZ itself has a well-formed ToC. Calibre reads the navigation structure and writes an equivalent ToC into the MOBI. 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 TXTZ and the MOBI 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 TXTZ 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 TXTZ and re-embedded in the MOBI at device-appropriate dimensions. You can also override it in Advanced by uploading a custom cover image alongside the book file.
RELATED CONVERSIONS
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Related comparisons
See these formats side by side to understand which fits your use case best.
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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.