OpenKoto

OpenKoto is an open-source, privacy-first language-learning app. Turn the articles, books, and videos you genuinely care about into study material, understand sentences in context, collect vocabulary, and review it on a schedule.

Key features:

• Paste text or import TXT, Markdown, and web content
• Import TXT and EPUB books with automatic chapter splitting, in either a sentence-by-sentence view or the book's original layout
• Import video and audio with SRT / VTT subtitles — or generate subtitles on device when you have none (requires iOS 26)
• Subtitles follow playback sentence by sentence; tap a line to jump to it, loop a single sentence, change speed without changing pitch, and hide the text to shadow by ear
• Read sentence by sentence, resume where you left off, and add bookmarks and highlights
• Show word-level readings above Japanese and Chinese text (furigana / pinyin), generated entirely on device
• Search the full text of everything you have imported — articles, book chapters, and media transcripts — and jump straight to the sentence
• Save vocabulary, organize word packs, and use spaced-repetition review; jump from any card back to the sentence it came from
• View reading and review statistics
• Use the app in English, Simplified Chinese, or Japanese
• Choose light, dark, and multiple visual themes
• Send web pages or selected text to OpenKoto from the iOS share sheet

Optional AI features use a bring-your-own-key model. Configure a compatible provider of your choice for translations and sentence explanations. API keys are stored in the iOS Keychain, while learning content and progress stay on your device. AI requests go directly from your device to your selected provider and do not pass through an OpenKoto app server.

No account is required. Sample articles are included, so reading, vocabulary, and review features work without configuring an AI provider.

OpenKoto is free and open source.