A free, fully in-browser tool for aligning two books in different languages sentence-by-sentence for creating Parallel Texts.
Upload a book and its translation (EPUB, PDF, or TXT), run the alignment pipeline entirely in your browser, then read the result as a paginated parallel ebook or export it as a TSV.
main-demo.mp4
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align_your_own_books.mp4
- Upload two books (source + translation) on the homepage, or try a built-in sample.
- Align — pick languages, click Align books; the model downloads once and runs in your browser.
- Read — popover view (tap a sentence for its translation) or side-by-side view (parallel columns).
- Export — download as TSV or EPUB from the alignment details drawer.
| Popover | Side by side |
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"This is completely useless, why not just read a book as is with a popup dictionary and be done with it?"
Yeah, normally I would agree, but I've recently had the misfortune of having a large portion of my time being forcefully spend on unimportant things like not immersing. I've simply decided that immersion, even if not "pure" immersion, is better than no immersion at all.
That being said, even if you find this useless, you might be interested in my upcoming project which aligns sentences and images instead.
- Three input formats — EPUB, PDF, and plain TXT.
- Aligns sentences in 50+ languages
- Fully in-browser ML — The model runs in the browser, so no need for a backend. The tradeoff is that you have to download a model.
- Two reading modes — popover view (tap a sentence to see its translation) and side-by-side view.
- TSV export and import — one sentence pair per row; gap rows preserved; any 2- or 3-column TSV works on import.
- Beginner learning with real content — align a book you're studying with a translation you already understand, then read sentence by sentence instead of grinding through a textbook
- Reading above your level — keep the original text in front of you while dipping into the translation only when you need it
- Reading way way way above your level — you've done one month of immersion and you're ready for 雪国. sure bro.
Similar to this — but instead of aligning two texts, it aligns sentences in a book with image frames from an adaptation (anime, movie, drama, etc.).
Upload a light novel (or any book) plus a video or frame dump from its adaptation, and read with the corresponding scene right next to each sentence. Think Monogatari stills beside the original LN narration, or Classroom of the Elite images next to the LN text.
Feel free to hmu if you find this interesting.
ETA: ~2-6 months.
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- Private / incognito windows — embedding models (up to ~1.2 GB) are cached via the browser's Cache Storage API so they don't need to be re-downloaded every session. Private/incognito windows back that storage with an ephemeral, memory-limited partition instead of disk (by design, so nothing survives after the window closes), and writing a file that large to it can silently fail. When that happens the model has to be re-downloaded on every alignment instead of being reused, and in the worst case the failed cache write can cause the alignment itself to fail. Use a normal window for a reliable experience.
ParallelTexts is licensed under the GNU General Public License v3.0.
Copyright (c) 2026, nullspace05.
Third-party components (including BSD-3-Clause code adapted from
ttu-ttu/ebook-reader) are listed in
THIRD_PARTY_NOTICES.md.
ParallelTexts would not exist without Transformers.js. The whole alignment pipeline — multilingual sentence embeddings, ONNX inference, running entirely in the browser with no backend — is built on @huggingface/transformers.
Parts of the paginated book reader and reading-progress system are adapted from ttu-ttu/ebook-reader (BSD-3-Clause), including:
- Character-count bookmarking (
exploredCharCountapproach) — seesrc/lib/reading-progress.ts - CSS multi-column pagination workarounds for iOS/iPadOS WebKit — see
src/components/paginated-reader.tsx
Full upstream license text: THIRD_PARTY_NOTICES.md.
The homepage example alignments use texts from the sources below. ParallelTexts only hosts the aligned exports — not the underlying books.
アリスはふしぎの国で / Alice's Adventures in Wonderland
- Original: Lewis Carroll (1865). Public domain.
- English: Project Gutenberg #11
- Japanese: translation by 大久保ゆう (Yuu Okubo), from Aozora Bunko (CC BY 4.0)
銀河鉄道の夜 / Night on the Galactic Railroad
- Original: 宮沢賢治 Kenji Miyazawa (1924). Public domain.
- Japanese: Aozora Bunko
- English: translation by Composer 2.5
Aventures d'Alice au pays des merveilles / Alice's Adventures in Wonderland
- Original: Lewis Carroll (1865). Public domain.
- French: translation by Henri Bué, Project Gutenberg #55456
- English: Project Gutenberg #11