Shinkansen

Shinkansen is a fast, smooth, privacy-first translation extension for web pages, YouTube subtitles, and PDF documents. Three things make it different: • Watch the page start turning into your target language within one second of pressing translate (Instant Translation, Gemini engine) • Text is replaced in place — fonts, sizes, colors, and layout are preserved; links, bold, and italics survive untouched • You bring your own API key; every setting lives on your own computer; your reading never touches a third-party server The name Shinkansen (新幹線, "bullet train") evokes a fast, smooth, frictionless reading experience. Translate into 8 target languages: Traditional Chinese, Simplified Chinese, English, Japanese, Korean, Spanish, French, German. The extension UI is available in the same 8 languages — pick independently or follow your macOS system language. • Multiple translation engines: Google Gemini (best-quality AI, requires API key), Google Translate (free, no API key), and any OpenAI-compatible model (OpenRouter, Claude, Ollama, etc.) • Single-language overlay / bilingual side-by-side modes — one-click toggle, with 4 visual treatments for the bilingual layout • YouTube subtitle translation: automatic detection and real-time replacement; styling matches native captions; bilingual subtitles available (two lines simultaneously) • YouTube AI smart segmentation: auto-generated captions are re-segmented by AI for natural full sentences • PDF document translation: PDFs parsed locally, translated, and rebuilt as a new downloadable PDF • Three customizable shortcuts: pick the right translation preset (engine, model, label) for the content you're reading • Auto-translate specific sites: add domains to a list — those sites translate on load • Cross-tab translation continuity: opening a link from a translated page auto-translates the new tab with the same preset • Translation cache + live cost report: translated content is cached (next time is free); toast shows token count, cache hit rate, and cost after each translation • Custom glossary: pin specific terms to your preferred translations (global and domain-specific layers) • Blocked-word list: explicitly tell the model to never use words you don't want in the translation • Edit translations: directly edit the translated text on the page after translation — handy for printing to PDF or letting Readwise Reader pick it up [Bring your own API key] Shinkansen doesn't sell translation as a service — you bring your own Google Gemini API key for AI translation. Gemini's generous free tier means everyday use is typically free (an entire Wikipedia article translates for under $0.08 with Flash Lite). If you'd rather skip the API key, the Google Translate engine works free with no setup. Step-by-step API key setup is in the GitHub repo. Shinkansen has no server, no telemetry, no analytics. Every setting lives only in your browser: • Your API key is stored locally in Chrome — never synced, never uploaded • Translation content is fetched directly from your browser to the corresponding engine endpoint (Gemini, OpenRouter, Google Translate) • Shinkansen never relays, caches, or logs translation content • The local translation cache lives in your browser only; clearing browser data wipes it Shinkansen is licensed under Elastic License 2.0; source is on GitHub. You're free to view, learn from, modify, and use it yourself, but cannot package it (or any modified version) as a hosted or managed service to third parties.