# WordByWord.io > Learn languages while browsing the web by highlighting, translating, and building vocabulary across websites, PDFs, and videos with AI-powered tools — and see in advance what share of any page or video you already understand. WordByWord.io is an AI-driven language learning service built around a Chrome extension and a web app. It helps learners immerse themselves in real content — articles, PDFs, YouTube videos — instead of artificial textbook exercises. Highlight any unknown word or phrase to translate it instantly, save it to a collection, and turn it into lasting knowledge with smart flashcards and adaptive training algorithms with spaced repetition. It supports 50+ languages to learn (including English, Spanish, French, German, Japanese, Chinese, Korean), and multiple languages can be learned at the same time. The web app interface is available in English, Russian and German. Vocabulary can be imported (CSV) and exported (Anki, CSV, PDF), and the community shares curated public collections. ## How It Works 1. Read what you love: read websites and PDFs or watch YouTube in your target language — the extension works everywhere. 2. Check the level before you start: Comprehension Level scores the page, video or PDF against your own vocabulary and shows the share of words you already know, sorted into four zones (Easy 95%+, Your level 85–94%, Challenging 70–84%, Too hard below 70%). It also lists the most frequent new words with a forecast such as "these 11 words add +6% understanding". 3. Discover and save new words: click any word or phrase to translate and save it in one tap. Spotlight mode highlights unknown words directly on the page, colour-coded by how well you know them. 4. Remember forever: smart flashcards (Word Player) and an AI trainer adapt to you, showing words at the right moment and in the right sequence, with clear progress tracking for collections and each word. YouTube integration: hover over words in subtitles to translate them, the video auto-pauses so you don't miss anything, and full sentences are displayed for context. A comprehension score for the video is computed from its subtitles before you press play. Comprehension Level details: a word counts as known only from the "Learned" level upwards; the ignore list, other writing systems, URLs and non-word tokens are excluded from the calculation; pages with fewer than 20 counted words get no score; 99.5% rounds down to 99, so 100% only appears at genuinely complete coverage. The score works in every supported learning language, because content is compared with the user's own vocabulary rather than with English. ## Core Content - [How it works](https://wordbyword.io/en#how-it-works) - [Pricing](https://wordbyword.io/en#pricing) - [FAQ](https://wordbyword.io/en#faq) - [Log In](https://wordbyword.io/en/auth/sign-in) - [Sign Up](https://wordbyword.io/en/auth/sign-up) - [Download Extension (Chrome Web Store)](https://chromewebstore.google.com/detail/wordbyword-%E2%80%93-translator-f/nnikiceohfnfopndpmmkkeojiijhcbbg) ## Pricing - Free Forever plan: translations, voiceover, collections and vocabulary tracking with no limits; includes 5 trainings and limited AI generations (10 AI term generations, 10 AI example generations per day). - Premium plan: unlimited trainings, unlimited AI term and example generation, enhanced natural voiceover. Yearly billing gives 2 months free. - Getting started is free: install the extension and sign in with a Google account. ## Docs - [Quick Start Guide](https://wordbyword.io/en/docs/quick-start): get started with WordByWord in minutes - [Chrome Extension Setup](https://wordbyword.io/en/docs/chrome-extension-setup): install and configure the browser extension - [Keyboard Shortcuts](https://wordbyword.io/en/docs/chrome-extension-keyboard-shortcuts): work faster with hotkeys - [Creating and Managing Collections](https://wordbyword.io/en/docs/creating-and-managing-collections): organize your vocabulary - [Generating Words with AI](https://wordbyword.io/en/docs/ai-term-generation): generate themed vocabulary sets with AI - [Importing Words from CSV](https://wordbyword.io/en/docs/csv-import): import existing vocabulary lists - [Training Modes Explained](https://wordbyword.io/en/docs/training-modes): ways to practice your vocabulary - [Flashcards (Word Player)](https://wordbyword.io/en/docs/flashcards): smart flashcards with spaced repetition - [Spotlight Mode](https://wordbyword.io/en/docs/spotlight-mode): see known and unknown words on any page - [Comprehension Level](https://wordbyword.io/en/docs/comprehension-level): see what share of a video, article or PDF you already understand before you start - [Reading and Translating PDFs](https://wordbyword.io/en/docs/pdf-translation): learn from PDF documents - [Learning with YouTube Subtitles](https://wordbyword.io/en/docs/youtube-subtitles): learn from video subtitles - [Learning Statistics](https://wordbyword.io/en/docs/learning-statistics): track your progress with detailed statistics and a contribution graph - [Free Plan vs Premium](https://wordbyword.io/en/docs/free-vs-premium): plan comparison - [Account Settings](https://wordbyword.io/en/docs/account-settings): manage your account ## FAQ - Is WordByWord free? Yes. The core features — translations, vocabulary tracking, and flashcards — are completely free with no limits. A Premium plan unlocks unlimited training sessions, unlimited AI generation, and enhanced voiceover. - How do I get started? Install the Chrome extension and sign in with your Google account — it takes just a few seconds. Then open any website and start highlighting words to translate and save them. - Does it work with YouTube? Yes. WordByWord integrates with YouTube subtitles: hover over words to translate them, save to collections, and the video auto-pauses. - How do I know whether a video or article is at my level? Comprehension Level shows the share of words you already know before you start — 95% and up is comfortable, 85–94% is the growth zone, below 70% is too early. It works on YouTube videos, any web article and PDFs, and it also lists the few frequent words that would raise the score the most. - What languages are supported? 50+ languages including English, Spanish, French, German, Japanese, Chinese and Korean. Multiple languages can be learned at the same time. - Is my data safe? Vocabulary and learning progress are stored to power the app and are never sold to third parties. See the Privacy Policy for details. ## Blog - [Language learning blog](https://wordbyword.io/en/blog): articles about vocabulary, memorization techniques and language learning habits - [Blog RSS feed](https://wordbyword.io/en/blog/rss.xml) ## Optional - [Privacy Policy](https://wordbyword.io/en/privacy-policy) - [Terms of Service](https://wordbyword.io/en/terms-of-service)