Look up whole phrases in the shows you watch.
Captionary is a free Chrome extension for YouTube, Netflix and Apple TV+. It puts a translation under the original subtitle. Click a word or drag across a phrase, and a tutor explains it in context using the AI you choose: your ChatGPT plan, your own API key, or a model on your own computer.
No account needed. Your saved words stay in your browser. Works on youtube.com, netflix.com and tv.apple.com.
Captionary runs in Chrome on a computer. Open this page there to install it.
Some meanings only exist as phrases
Look up cuenta and you get “bill”. In se dio cuenta it means “realized”, and no single word in the line tells you that. Phrasal verbs, idioms and set expressions work the same way in every language.
- Drag across the words, or click one and Shift+click another.
- With a tutor connected, click a single word and it names the phrase the word belongs to. One more click looks up the phrase instead.
- Phrases are saved in dictionary form. Se dio cuenta goes into your list as darse cuenta.
- Works in Chinese, Japanese and Thai too, where words aren’t separated by spaces.
mi hermano se dio cuenta de que…
- Word by word
- himself · gave · bill
- As a phrase
- darse cuenta · to realize
Bring the AI you already pay for
Captionary doesn’t sell AI credits or lock you to one model. Connect what you have and switch whenever you like.
- Sign in with ChatGPT
- Use your ChatGPT Plus, Pro or Business plan. No API key and nothing extra to pay; requests count toward your plan’s Codex usage limits.
- Use your own API key
- OpenAI, Anthropic (Claude), Google Gemini, OpenRouter, DeepSeek, Groq, Mistral, xAI, or any OpenAI-compatible endpoint. You pay the provider directly, at their prices.
- Run it on your computer
- Ollama, LM Studio, or Chrome’s built-in Gemini Nano. Nothing leaves your machine.
Give each job its own model: a fast, cheap one for word look-ups and a stronger one for sentence breakdowns. Add a fallback for outages and rate limits. Answers are cached, and an optional daily cap stops runaway spending.
- ChatGPTSigned in
- Anthropic (Claude)API key ••••3f9a
- OllamaOn this computer
- Word look-up
- Ollama · Qwen 2.5
- Sentence breakdown
- ChatGPT · GPT-5.5
- Follow-up chat
- Claude Sonnet 5.5
- Subtitle translation
- Claude Haiku 5.5
- If a provider fails
- Try ChatGPT
Your word list is free, and it stays yours
Save a word or phrase as learning or known. Captionary keeps the sentence, its translation, the video and the timestamp it came from. Learning words get a dotted underline wherever they turn up again: in subtitles, the subtitle list and the reader.
- Review with flashcards.
- Export to Anki or CSV, or keep a JSON backup.
- No account and no subscription. The list lives in your browser.
-
darse cuentaLearningto realizeAl final, mi hermano se dio cuenta de que yo tenía razón.
-
気がつくLearningto notice; 気がついたら, before I knew it気がついたら、もう朝になっていた。
-
tener razónKnownto be right
Captionary and Language Reactor compared
Language Reactor is the best-known tool for learning from Netflix and YouTube, with two million Chrome users, and it does a lot well. This is where the two differ. We checked every Language Reactor detail against its own pages on October 18, 2026.
| Feature | Captionary | Language Reactor |
|---|---|---|
| Look up several words at once | YesDrag across them, or Shift+click | NoOne word at a time. Its team said in June 2026 that it’s under consideration.1 |
| Save words and phrases | FreeFlashcards, Anki and CSV export included | ProFree only inside its PhrasePump drills2 |
| AI explanations | You set the capWord explanations, sentence breakdowns and follow-up chat, up to your provider’s limits and a daily cap you can change (300 requests by default) | 5 a dayLexa AI: five free questions a day when signed in, unlimited with Pro3 |
| Choose the AI model | YesChatGPT sign-in, 8 cloud providers with your own key, any OpenAI-compatible endpoint, or local models | NoLanguage Reactor’s own AI |
| Translation on Netflix when there’s no subtitle in your language | FreeChrome’s on-device translator, or your AI | ProMachine translation, about 5 hours of new content a day4 |
| Apple TV+ | YesPlus YouTube and Netflix | NoYouTube and Netflix5 |
| Account | NoneEverything is stored in your browser | NeededFor Pro, Lexa questions and sync |
| Price | FreeYour AI provider bills you for what you use, if anything | FreemiumPro is a monthly, 3-month or yearly subscription2 |
Where Language Reactor is ahead
- Its website works on phones and tablets. Captionary is desktop Chrome only.
- Settings, saved words and chats live in your account and follow you across devices. Captionary has no sync; you move a JSON backup yourself.
- With Pro, it makes subtitles by speech recognition, including for dubbed Netflix audio.
- It has a catalog of videos, books and podcasts, a chat partner called Aria, and an English course in beta.
- Its Anki export includes images and audio. Captionary exports text: the word, its meaning and the sentence.
What both do
Dual subtitles, a subtitle list, auto-pause and line repeat, keyboard shortcuts, transliteration, word-frequency colors, a text reader, local video files with your own subtitles, and Anki export.
Which to pick
Pick Captionary if you want to look up phrases, choose your own AI, or keep a word list without paying. Pick Language Reactor if you study on your phone, want your words in an online account, or watch dubbed Netflix shows that have no subtitles.
- Language Reactor forum, staff reply of June 26, 2026: How to select multiple word definitions?
- Language Reactor Pro page
- Language Reactor update history, September 2026
- Language Reactor FAQ
- Language Reactor on the Chrome Web Store
Language Reactor is made by Dioco. Captionary is independent and not affiliated with it. If something here is out of date, open an issue and we’ll correct it.
The rest of the toolkit
- Fits each player
- Captionary’s button sits in the player’s own control bar, and its menus and look-up card take the site’s look and font.
- Translation from the best source
- A human subtitle track when there is one, then YouTube’s auto-translate, then Chrome’s on-device translator, then your AI. Blur it until you hover, to test yourself.
- Subtitle list
- Follows playback. Search it, jump to any line, copy it, or download an .srt with both languages.
- Romanization
- Pinyin with tone marks, romaji for kana, and romanized Korean, Russian, Greek and more, under the original line.
- Sentence breakdown
- Press E for the current line’s translation, a literal gloss, its chunks and its grammar points.
- Playback for study
- Pause after every line, repeat it, step back or forward, change speed. A S D by default, and every shortcut can be remapped.
- Word frequency
- Optional underlines show how rare a word is in film and TV subtitles, so you know which ones are worth saving.
- Reader
- Paste text, open .txt, .srt or .vtt files, or right-click any web page to read it with clickable words.
- Your own videos
- Play a video file from your disk with its subtitle file and get the same overlay, list and look-ups.
Your keys and your words stay in your browser
There’s no Captionary account, no analytics and no ads. The code is on GitHub, so you can check all of this yourself.
- API keys and ChatGPT sign-in tokens are kept in the extension’s local storage on your computer. They’re never synced or exported, they go only to the service they belong to, and web pages can’t read them.
- Chrome asks your permission for each AI service when you add it, one site at a time, and Captionary gives the access back when you remove the service. ChatGPT sign-in also needs localhost for a moment, to read the result of OpenAI’s sign-in page; that access is given back as soon as you’re signed in.
- You choose how much context goes with a request: just the word, the sentence, or a couple of lines around it, and whether the video title is included.
- Subtitle text is marked as untrusted in every prompt, and answers can’t load images or HTML.
Questions
Is Captionary really free?
Yes. The extension is free. If you connect a paid API, the provider bills you for what you use. With ChatGPT sign-in, a local model or Chrome’s built-in AI, there’s nothing extra to pay.
Do I need an API key?
No. Dual subtitles, translations, the dictionary, saving words and review all work without any AI. For the tutor, you can sign in with ChatGPT, run a local model, or use Chrome’s built-in AI instead of a key.
How does “Sign in with ChatGPT” work?
You sign in on OpenAI’s own page, the same way OpenAI’s Codex CLI does, and Captionary uses your ChatGPT Plus, Pro or Business plan. Requests count toward the plan’s Codex usage limits. OpenAI hasn’t documented this route for other apps, so it could change. If it does, API keys and local models keep working. Captionary isn’t affiliated with OpenAI.
How much will my API key cost me?
That depends on the provider and model you pick. Captionary keeps it down: explanations are only generated when you ask, answers are cached, and you can set a daily request limit. The settings page counts requests and tokens for each model.
Which languages does it support?
Any language the video has subtitles in. Phrase selection also works in Chinese, Japanese and Thai, and romanization covers Chinese, Japanese kana, Korean, Russian, Ukrainian, Bulgarian, Serbian, Greek and more. The tutor answers in your own language.
Which browsers and devices?
Desktop Chrome. Captionary doesn’t run on phones or tablets.
Is Captionary connected to YouTube, Netflix, Apple or Language Reactor?
No. Captionary is an independent extension. Netflix and Apple TV+ need their own subscriptions, and subtitle availability depends on the video.
Try it on the next thing you watch
A short setup guide asks which language you’re learning and helps you connect a tutor, or skip that for now.
Add to Chrome, it’s free