ttu-reader: The In-Browser E-Reader for Japanese
ttu-reader lets you read Japanese ebooks with Yomitan in your browser. It is a free, in-browser EPUB reader built so hover-dictionary popups work on real Japanese books.12 For an N4+ reader moving into native EPUBs, the promise is simple: upload a book, hover any word, and mine it straight to Anki.
What ttu Is
The reader's canonical name is ッツ Ebook Reader, written with the leading katakana ッツ in both the repository heading and the live application's page title.13 The repository slug is ttu-ttu/ebook-reader. The Yomitan documentation calls the tool "Ttsu Reader," and the community spellings "ttu," "ttsu," and "ttu ebook reader" all point to this one project.12
Its one-line self-description is "An online e-book reader that supports dictionary extensions like Yomitan."1 The live application runs at https://reader.ttsu.app.3
The project is maintained by the GitHub user ttu-ttu and released under the BSD-3-Clause license, a permissive open-source license.1
The repository describes itself as "Currently not actively worked on / Maintenance only."1 That is a statement of the project's posture, not a warning about stability; the reader continues to work as documented here.
Why a dedicated reader instead of Kindle or a generic EPUB app
ttu renders book text as ordinary, selectable HTML in the browser. The Yomitan documentation states the underlying principle: "Readers allow reading books and text on your browser which makes the text you read Yomitan-compatible."2
Because the page is normal web text, a browser dictionary extension can scan the characters under the cursor. It is not a canvas image or a DRM container that paints inaccessible glyphs. This is the property that generic store apps and image-based renderers typically lack.2
The Yomitan wiki lists ttu among browser-based readers and describes it as "A minimal e-book reader that loads HTMLZ, Plain Text and EPUB files. Supports offline mode that makes this ideal for mobile and e-readers."2
What it costs and what it runs on
ttu is free and open-source under BSD-3-Clause, and reading a local book requires no account.1 It is a browser application. The README lists "Installation and offline capabilities," meaning it can be installed as a Progressive Web App and used offline after the initial load.14
The Yomitan wiki corroborates the offline behaviour, noting that the reader "Supports offline mode that makes this ideal for mobile and e-readers."2
Getting Your Books In
Supported formats and the dropzone
ttu loads three formats: the README states it "Supports HTMLZ, Plain Text and EPUB files."14 For Japanese reading the common input is an EPUB, but HTMLZ and plain text work the same way.
| Format | Typical source |
|---|---|
| EPUB | Novels and light novels bought or exported as plain (unencrypted) EPUB |
| HTMLZ | Zipped HTML, often produced by a converter such as Calibre |
| Plain text | Scraped or exported running text |
The reader's import surface is its book manager, which the README lists alongside "Data import/export via local and external sources."4 You add a book by clicking the dropzone on the manager or dragging a file or folder onto it. Where the book itself comes from is the reader's own concern, not something this guide advises on.4
The book manager and library view
The README explicitly lists a "Book manager," which is the home screen for your library.4 It presents books as a cover grid with titles. From there, you can open a book, switch between books, and remove one you no longer need.
Each book carries its own reading position. The README lists "Character count and progress display," and the manager shows that per-book progress. You can see how far you are into each title before opening it.4
Reading and Formatting
Fonts, size, and line spacing
ttu exposes a "Customizable environment (themes, font size, image blur, furigana settings)."4 Font size is adjustable directly from that environment, which matters for Japanese because small kanji lose the stroke detail that distinguishes similar characters.
The reader also lets you choose a font family and adjust line height.43 A Japanese-capable font and generous line spacing reduce eye strain across the long sessions that extensive reading depends on.
Furigana, writing direction, and themes
Furigana display is one of the customizable settings named in the README's environment list.4 You can turn the reading aids on when you want support, or turn them off to test unaided recall.
Writing direction is switchable. The README lists "Vertical/Horizontal reading modes," so both tategaki (the vertical layout used by most Japanese print fiction) and yokogaki (horizontal layout) are available.4 Themes and an image-blur setting round out the environment. Image blur is useful for covers or illustrations you would rather not see in a public space.4
Making Yomitan popups work in ttu
Yomitan compatibility is the reader's design goal, restated in its own subtitle: "An online e-book reader that supports dictionary extensions like Yomitan."1 Because ttu is a normal web page served from reader.ttsu.app, Yomitan scans its text the same way it scans any website.32
One consequence is worth stating plainly: the hosted app does not need the "Allow access to file URLs" permission. That permission concerns extensions reading local file:// pages, which is not how you reach the hosted reader. If you have already set Yomitan up, reading on reader.ttsu.app needs no extra extension permission.
The reader's setup is covered in Yomitan (Yomichan): The Hover-Dictionary Workflow. This article assumes that work is done and the extension is installed.
The README warns that with wheel navigation enabled, "mouse wheel clicks are intercepted and may not work as expected. E. g. for Yomitan you need to keep the wheel pressed while moving the cursor."4 If a Yomitan scan does not fire in pagination mode, hold the mouse wheel down while you move the cursor over the word, or turn wheel navigation off.
History and Progress Tracking
Per-book progress and statistics
ttu keeps reading statistics, not just a bookmark. The README lists a "Time/Character and Reading Goals Tracker" and "Reading Data Statistics."4
The statistics view reports reading time, characters read, minimum and maximum reading speed per hour, and the dates a book was started and finished.3 These figures let you measure reading volume instead of guessing at it. Reading volume is the metric that extensive reading is built on.
Bookmarks come in two forms. The README lists "Auto bookmark functionality," which records your position automatically so you resume where you stopped. The live app adds a manual bookmark and a return-to-bookmark shortcut.43
Syncing across devices
By default, ttu is local-first: your library and progress live in the browser, and the README's import/export runs "via local and external sources."4 Sync is optional. You turn it on yourself, rather than having your data uploaded by default.
Two cloud providers are supported for carrying reading data and your library between machines: Google Drive and OneDrive.43 The README also offers a desktop-only filesystem option and zip export/import. Those are manual transfer paths rather than cloud sync, so the cloud-provider count is two, not four.4
ttu in the Mining Loop
ttu is where the hover-dictionary and the card-creation workflow meet a real book. The loop is short and repeats on every unknown word: load the book once, then read, hover, and mine without leaving the page.
From hover to Anki card
ttu's contribution to mining is one fact: it presents selectable web text that Yomitan can scan, so any word you hover can become a card.12 The card-creation mechanics themselves belong to Yomitan + Anki: One-Click Card Creation. That article covers the path from the Yomitan popup's add button to the Anki note that lands in your deck.
The wider method is the subject of Sentence Mining: Building Your Own Japanese Anki Deck From What You Read. That includes choosing which sentences are worth keeping and how to format the cards.
What to read in ttu
ttu loads EPUB, HTMLZ, and plain-text books, which makes native prose its natural input.4 Novels and light novels exported as plain EPUB are the obvious starting material. Both come in a format ttu reads and reward the hover-and-mine loop with a steady supply of new words.
For where to begin with that material, see Reading Japanese Novels: Where to Start and Reading Japanese Light Novels: The Stepping Stone Between Manga and Novels.
Good to know
DRM-locked store books will not load
ttu parses plain EPUB, HTMLZ, and plain-text files.14 A DRM-encrypted EPUB sold by a store is an encrypted container rather than a plain EPUB, so it does not open in ttu as delivered. Treat this as a format limitation: the book has to be a plain EPUB before ttu can read it. Handling store DRM is something you deal with outside the reader. For reading inside a store's own DRM container instead of converting out of it, see Kindle for Japanese Learners.
Local-first means clearing browser data wipes your library
Books and reading data are stored locally in your browser storage, and the app requests persistent storage to hold them.4 Clearing the browser's site data therefore removes the locally stored library and progress. To avoid that, first export them or enable sync through Google Drive, OneDrive, the filesystem option, or a zip export.4
Page-turn vs continuous scroll preference
ttu offers both layouts: the README lists "Continuous/Pagination reader modes," and continuous mode includes an "Auto scroll" option.4 Pagination mode mimics turning pages. Continuous scroll suits long extensive-reading sessions where stopping to turn a page would break the flow. Which you prefer is a matter of reading habit, not a setting you have to get right.
See also
- Mokuro: OCR for Japanese Manga
- ASBPlayer: Subtitle-Based Sentence Mining for Anime
- When to Look Up a Word vs. Infer It (Japanese)
- Manga for Japanese Learners: A Difficulty-Sorted Guide
- Building a Daily Japanese Reading Habit
- Tracking Japanese Progress: What to Measure and What to Ignore