DualBook 8 languages

Free online tool — no sign-up

Translate an English book into Japanese

Upload an English EPUB and get the first fifteen pages back in Japanese. The decision that shapes the whole translation is which speech level each character uses — and the English never tells you.

The first 15 pages of text are sent to our server to be translated. The file itself stays on your device.

Translating into Japanese means supplying information the English original never contained. Every line of dialogue needs a speech level: does this character speak in keigo, in plain form, roughly? English marks none of it. The translator infers it from who the characters are to each other — which means knowing, before starting.

Reading the whole book first is what makes that inference possible. The guide records each character and their standing, so a subordinate still speaks to their superior the same way in chapter fifteen as in chapter one.

First-person pronouns are the same decision in miniature. I becomes 私, 僕, 俺 or あたし depending entirely on who is speaking, and switching between them mid-book makes one character read as two.

How it works

  1. Choose your English EPUB

    A DRM-free EPUB. The file stays on your device; only the text is sent.

  2. The model reads the whole book

    Each character's standing and speech level is decided once, from the whole book — information the English never stated.

  3. The first 15 pages come back in Japanese

    About 4,500 words, translated as continuous prose so register stays even across the sample.

  4. Download, or read it here

    A complete EPUB. Japanese needs CJK glyphs, and the file keeps its own fonts and stylesheets.

What this free tool does not do

No furigana is added. Ruby has to be authored; a translation cannot invent readings for a text that never had them.

The output stays horizontal. We keep the book's existing stylesheets rather than imposing vertical writing mode on a book never laid out for it.

Fifteen pages, not the book.

Speech level is inference. The guide keeps it consistent; a human translator who knows the book may still choose differently.

Questions

Can I choose the speech level?

Not directly. The model decides once, having read the whole book, and holds that decision to the end. What you get is consistency rather than control.

Is furigana added?

No. Ruby belongs to a Japanese original and does not exist in an English source book, so there is nothing to carry across.

Does the output become vertical text?

No. The book's own styling is preserved — forcing vertical writing on a horizontally-designed book breaks its layout.

How much is free?

About 4,500 words, roughly fifteen pages. Measured in words, so long and short books get the same allowance. Five books a day.

Translate the whole book

The app translates the entire book with the same engine and shows the Japanese beside the English.

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