Lingoku: Browser extension replacing English words with Japanese vocabulary.

What it does

Lingoku is a browser extension that annotates Japanese text across websites with furigana (phonetic readings), kanji explanations, and word meanings. When hovering over unfamiliar kanji or words, users see contextual explanations powered by an LLM backend. The tool works on video subtitles from Netflix and YouTube, news sites, social media, and any webpage containing Japanese text. Users can save words with one click, which automatically generates flashcards with the original sentence, reading, meaning, and JLPT level.

Who it is for

The extension targets English speakers learning Japanese who consume Japanese media like anime, J-dramas, and news. The tool applies the comprehensible input (i+1) method—learning from content slightly above current skill level. It suits learners who already spend time on these platforms and want passive vocabulary acquisition without switching to dedicated learning apps.

Pricing

The site indicates a free basic plan with permanent access. A Chrome, Edge, and Firefox extension is available. Installation requires 30 seconds and no sign-up.

How it stands out

Lingoku positions itself around context-aware learning rather than isolated vocabulary drills. The LLM backend detects word sense from surrounding dialogue—distinguishing homographs and false cognates that confuse learners (for example, the kanji 手紙 has different meanings depending on context). The extension identifies keigo politeness levels automatically and tags words with JLPT difficulty levels. Integration into everyday browsing—anime, news, social media—avoids forcing habit changes or app-switching.

What a founder should check

A rival builder should verify how many active learners already use Lingoku's approach and whether the free model generates sufficient data to improve the LLM. The competitive moat depends on the quality of context-aware explanations; if the AI simply looks up dictionary definitions, switching costs are low. Third, examine pricing strategy—Lingoku currently offers free access, so a paid competitor must clearly justify premium features (faster explanations, offline mode, better spaced repetition) or risk losing users to the free version.

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