Bunkai

Bunkai (分解, “breakdown”) is a Chrome extension for people learning Japanese. Highlight any Japanese text on any webpage and a popup appears with the sentence translated naturally into English, followed by a per-word analysis: reading in hiragana, part of speech, dictionary meaning, and what the word is actually doing in that specific sentence.

Dictionary lookups tell you what a word means. Bunkai tells you what it means here.

How it works

Four files carry the whole extension:

• manifest.json: Manifest V3 declaration, permissions (activeTab, scripting, contextMenus, storage), content script matches on <all_urls>
• content.js: injected on every page, listens for text selection, positions and renders the breakdown popup
• background.js: service worker that receives the selected text, calls Gemini, and returns structured JSON back to the content script
• popup.css: Catppuccin Mocha color palette, dismisses on outside click

A separate settings.html + settings.js handles the extension popup for storing your Gemini API key in chrome.storage, with two toggles: enable/disable the extension globally, and require Shift+highlight to trigger analysis (on by default, so casual selecting doesn’t burn quota).

Design

The icon is the kanji 分 in a pink-to-purple gradient on a transparent background, designed in Inkscape and exported at 16 / 48 / 128 px for the manifest.

Stack

• JavaScript, no framework and no bundler. The whole extension ships as raw files.
• Chrome Extensions API on Manifest V3
• Google Gemini API with gemini-2.5-flash-lite for the breakdown, prompted for a strict JSON schema so the popup can render each field without any parsing acrobatics