AI agent for learning languages
Learn English from anything you love
Add a video, book or article, or ask for a topic. Subtlex turns it into English lessons at your level.
If you can watch it, read it or paste it, you can learn English from it
In Subtlex, you choose what you study.
so honestly, I procrastinated for weeks
Videos
The YouTuber you watch every week
00:41:07,220 → 00:41:09,010
You don’t get to walk away from this.
00:41:09,400 → 00:41:12,150
I’m not bailing on you. Not this time.
00:41:12,600 → 00:41:14,000
Shows & movies
The series you’re watching, through its subtitles
CHAPTER ONE
It was a bright cold day in April, and the clocks were striking thirteen. Winston slipped quickly through the glass doors…Books
The novel on your nightstand, in the original
medium.com/@anna.kowalski/why-remote-teams-end-up-writing-more-3f9c2e1a7b4d
Why remote teams end up writing more
Async work forces you to be explicit about decisions that used to happen in hallways.
Articles
News, blogs, docs: anything with a link
hey, can we push the call to Thursday?
sure, I’m swamped today anyway
perfect, talk soon
Any text
Emails, chats, lyrics, notes: paste them in
Write a dialogue at a coffee shop. I’m B1, I want to sound more natural
topic · B1
Any topic
Nothing at hand? Ask, and the agent writes it at your level
Subtlex counts every word and tracks how well you remember it
- 01
Builds a word base from your content and counts every word, in any form
Other AIs only guess these numbersHow we ship 100 times a dayYouTube video- the×182
- we×96
- shipships · shipped×41
- release×23
- roll backrolled it back×12
- bottleneck×9
- 02
Picks the most frequent words in your content that you don’t know yet
Other apps give everyone the same list84% words known- theI know
- weI know
- shipNew
- releaseI know
- roll backNew
- bottleneckNew
- 03
Gathers a word from all your courses: the more real examples, the better you remember it
Other AIs don’t build your personal word basebottleneckCode review was our biggest bottleneck.How we ship 100 times a dayIn a remote team, one slow reply becomes a bottleneck.Why remote teams end up writing moreHow would you find the bottleneck in this service?Mock interview: backend developer - 04
Knows when you’ll forget each word and brings it back right before
Other AIs don’t know your memorybottleneckReinforcingreviewed every 4–20 daysNext review in 6 days4 reviews · 3 rightOct 9Oct 10Oct 13Oct 19
They teach sentences nobody says
Other apps
Subtlex
Same catalog for everyone
Your own content
Made-up sentences
Real English
Stop helping around B1
Grow with you, beginner to advanced
Lessons on their schedule
Lessons on your goals
Everything a tutor would do
Code review was our biggest bottleneck.
bottleneck/ˈbɒt.əl.nek/
AI definition in context
Here: the step that slows the whole team down.
Ask AIUnderstand every word
Tap any word to get its meaning in that sentence, hear it and see how it’s used. Still unsure? Ask the AI.
Next
WritePractice every skill
Listen, speak and write with your new words. The AI corrects you when you speak.
bottleneckreview today
roll backin 2 days
ship itin 6 days
deployin 3 weeks
meetingknown
Never forget what you learned
Subtlex reminds you about each word at the right moment and skips the ones you know.
Whatever you’re learning English for
Start with a ready-made video or article for your goal, or ask the agent for anything else.
Starting from zero? We’ll go slower.
Tap “I'm a complete beginner, skip the test” and get 31 ready-made lessons in order, from greetings to talking about yesterday. The agent keeps its sentences short and explains everything in your language.
Pay only for what you use
No subscription. You pay in tokens, and each AI action costs what it uses.
Why I built Subtlex
I’m Leven, an engineer and team lead who left a big corporation to build Subtlex on my own. I love learning languages, and I was tired of apps that stop being useful once you pass the basics.
None of them would let me learn from the new Spider-Man movie, a book I’d just bought or the game I was playing. So I built one that learns from whatever you care about.
I read every message, so I’d love to hear your feedback.
FAQ
YouTube videos, subtitles, books, articles and websites, or any text you paste. You can also ask the agent to write something on any topic.
It analyzes all of your content first: it counts every word and phrase precisely, and how often each one appears. Then it gives you the most frequent ones you don’t know yet. They make up most of the text, so every word you learn makes more of it clear, and you understand it faster.
Any, from your very first words to advanced. A 30-second test sets your level, and every lesson follows it as you grow. Starting from zero? Choose “I'm a complete beginner, skip the test” and get a ready-made path of 31 beginner lessons in order: each one becomes a course in a tap, and the agent keeps its sentences short and explains everything in your language.
ChatGPT waits for your question, then forgets the answer. Subtlex builds each day’s lessons from the words that are due and reminds you to take them. Reviews follow FSRS, a spaced repetition model from memory research, so a word comes back shortly before you’d forget it. Subtlex picks the words to learn by how common they are and by your level. Every word you know or learn sits in your personal dictionary, with examples from all your courses. Subtlex stores this exact data about you and your learning in your account. A neural network sees only the chat’s context. That context has a size limit, the network compresses long conversations, and a new chat starts from zero. So it can only guess data like this.
Duolingo keeps you busy with points, gems and streaks, and everyone gets the same made-up sentences. Subtlex has no points to chase. Every lesson is made only from your content and your words: the ones you don’t know yet, from the series you watch or the book you read. You read and watch them in context, then listen, speak and write until they stick, so no minute goes to words you’ll never use. And the more content you add and lessons you take, the better the agent knows you and the more precise it gets, from beginner to advanced.
What you spend on AI features. You start with 200,000 free ones, and each action costs what it uses.
Not a language learning game
Learn English from what you love
Your videos, books and texts, turned into English lessons.