I built a Chrome extension to make Japanese katakana loanwords easier to read — meet YomiMark

For a developer still learning Japanese, nothing is more frustrating when reading Japanese tech pages than this:

• A wall of kanji — you know what they mean, but not how to pronounce them.
• A wall of katakana loanwords — you recognize every character, yet can't tell what they spell out together. "コンテキスト" is obviously the English word Context, but it takes you several seconds to register.

Like this:

There are plenty of furigana-style annotation extensions out there, but I couldn't find a single one that handled katakana loanwords.

So I decided to build my own. I named it YomiMark.

Its mission is simple: show up only when you need it, and give you the most precise help when you do.

Here's what it looks like in action:

Why YomiMark? The three principles

Three design principles guided the build.

1. Minimalism: select-to-annotate, never intrusive

I didn't want the extension to disrupt the visual flow of any page. YomiMark uses a select-to-trigger flow — annotations only appear after you select some text and click a small purple button. The interaction encourages "read first, look up second," which actually helps long-term memory for learners.

2. More than kanji: a rescue line for katakana

This is YomiMark's signature feature. It doesn't just add furigana to kanji — it ships with a built-in loanword dictionary. Select a word like "イノベーション" and it doesn't just tell you the kana reading; it shows you the original English word (Innovation). For beginners surfing tech docs, this is a game-changer.

3. Privacy and speed: fully offline

I don't believe everything needs to go through the cloud. YomiMark bundles the morphological analyzer (kuromoji.js) and the full dictionary directly inside the extension. That means selected text never leaves your browser — preserving your reading privacy and delivering instant response without waiting on network latency.

Feature highlights

• Smart tokenization — built on a mature morphological engine that detects word boundaries accurately.
• Native rendering — uses the HTML standard <ruby> tag, so annotations look as natural as a textbook and adapt to any font style.
• Dark mode — the popup ships with a minimal, refined dark theme. Taste matters.
• Fully customizable — find the default colors too subtle? Adjust the kanji and loanword annotation colors freely in settings.

Who is YomiMark for?

• IT professionals browsing Japanese corporate sites or tech docs who need to pick up domain vocabulary quickly.
• News readers working through NHK News or Yahoo Japan who keep getting stuck on dense place names and political terms.
• JLPT learners training real-world reading instincts on actual web pages.

Getting started

YomiMark is in active V1 iteration. Grab it from the Chrome Web Store.

1. Select text — just like copying text, highlight the Japanese you want to read.
2. Click "読" — a small button appears above your selection.
3. Instant unlock — annotations appear right away.
4. Personalize — pick the annotation colors that suit your eye.

Closing notes

YomiMark grew out of my own pain point as a developer learning Japanese — wanting katakana loanwords to feel a little less alien.

I hope this small extension can be a stepping stone on someone else's Japanese journey. If you find it useful, please share it with anyone else still climbing the same hill.

Developed with care by Toshiki.Tech