Learn Spanish in
your own words.
Cielo reads the WhatsApp chat you have with your favourite person, finds the things you say most, and teaches you the Spanish for exactly those. The chat never leaves your phone.
Free Android app. No account needed.
Your chat
omw to the office, call me when you’re free12:31
Did you eat? Don’t skip lunch12:45
I’m home. I miss you so much19:15
Good night, I love you22:10
What you say most
- did you eat×5
- on my wayfrom “omw”×4
- i miss you×3
- i love you×3
In Spanish
- ¿Ya comiste?The “ya” makes it sound caring.
- Voy en caminoon my way
- Te extrañoi miss you
- Te quieroi love you
Your lesson
Build it in Spanish
“did you eat”
¿Yacomiste?prontocasa¡Perfecto!
Every lesson starts with something you said.
Cielo turns your top phrases into a path, grouped by topic: a few new ones each day and a recap to close it. There are five kinds of exercise: meet, pick, build, match and type.
Meet each phrase beside the message you actually wrote.
Build it from word tiles.
Type it. Missing accents and small typos are forgiven, and you always see the exact form.
Finish the lesson; missed answers come back before the end.
Spaced review. Every phrase gets a memory card (FSRS), so it comes back just before you would forget it, with a gentle daily streak.
A beginner day you can skip. “Primeros pasos” covers greetings first; if you know them, a short test lets you move straight to your own phrases.
It reads the way you text.
Real chats are messy. Before counting anything, Cielo cleans each message: links, numbers and @mentions go, and the words are repaired so “omw” and “on my way” count as the same thing.
- omw
- on my way
- Texting shorthand is expanded.
- tommorow
- tomorrow
- Typos are fixed with a 50,000-word dictionary.
- loooove
- love
- Stretched words are shortened.
- Kemi
- Kemi
- Names are never changed, and never taught.
Then it counts phrases up to six words long and ranks them by how often you use them. Out of the box it learns only from your own messages.
Your chat never leaves your phone.
A chat with your favourite person is private. Cielo is built so it can teach you without ever uploading it.
Sign-in and backup are switched off in the current Android build.
Read on your phone
The export is parsed on the device and kept in Cielo’s private storage. No server ever receives it.
Your messages, not theirs
By default Cielo learns only from what you wrote. Your person’s messages are used only if you switch that on.
Backup without message text
The optional backup keeps progress only: phrases, finished lessons, memory cards and your streak. The server rebuilds every upload from known fields, so nothing else can ride along.
See it in 43 seconds.
From opening the app and importing the sample chat to finishing the first lesson, recorded on an iPhone simulator with nothing sped up but the pauses.
The APK installs on Android phones. An iPhone version needs an App Store release first.
Under the hood
Cielo is a complete app, from the text-processing pipeline to the backend, and every line of it is open.
- Text pipeline
- Parses iOS and Android WhatsApp exports (both date orders, 12- and 24-hour clocks, multi-line messages), strips links and numbers, detects names, and ranks phrases of up to six words. TypeScript, on the phone.
- Spelling repair
- A self-contained SymSpell module with a 50,000-word frequency dictionary. It fixes typos and stretched words while leaving names and slang alone.
- Learning
- A topic-based path, five exercise types with accent- and typo-tolerant grading, and FSRS spaced repetition.
- App
- React Native with Expo SDK 57, Expo Router, SQLite on the device, Reanimated for motion, light and dark mode.
- Backend
- Expo Router API routes, Prisma with Neon Postgres, and Better Auth for Sign in with Apple and Google.
- Quality
- 69 unit tests with node:test. The app icon and splash screen are generated from code.