Code together,in real time.
Pair in one shared room, watch your code run step by step, and practice 100 interview problems together, right in the browser.
Free · No install · Python, JavaScript and TypeScript
Everything in one room
The platform
One room. Everything you need to get better.
Pair on code, watch it run, practice interview problems and track your progress, all in the browser.
01 · Collaborate
Edit together. Never collide.
Everyone types in the same file at the same time, and every edit merges cleanly. Live cursors and selections show who's where, and Follow mode rides along with a teammate.
- Conflict-free editing
- Live cursors and selections
- Follow mode
- ⌘Z only undoes your own edits
02 · Lens
Watch your code run.
Step through Python, JavaScript or TypeScript one line at a time. Arrays get index markers, tables become grids, and linked lists and trees are drawn as they change. In a room, everyone sees the same step.
- Index markers on every array
- Linked lists, trees and grids
- 40 ready-made concepts
- Shared in every room
03 · Practice
100 problems, tested in the browser.
Classic interview problems from Easy to Hard, with instant tests in Python, JavaScript and TypeScript. Work alone, or share the link and solve it together.
- Instant test results
- 35 Easy · 46 Medium · 19 Hard
- Solve with a partner
- Every solve tracked
04 · Big-O meter
Know your Big-O as you type.
A live meter reads your code and shows its time and space complexity. Rewrite a nested loop and watch O(n²) become O(n).
- Time and space complexity
- Updates as you type
- Right there in the editor
05 · Progress
See yourself improve.
Your dashboard tracks the problems you've solved, your active days and streak, and the people you've coded with.
- Progress by difficulty
- 16-week activity map
- Streaks and coding partners
Features
Everything a pairing session needs.
One room for your code, your team, and the conversation around it.
Conflict-free editing
Type at the same time as everyone else. Edits merge cleanly, your cursor stays put, and ⌘Z only undoes your own changes.
2 people online
Live presence
See who's in the room and where they're working. Click Follow to ride along with anyone.
Built-in chat
Talk it through without leaving the editor, with reactions, inline code, and typing indicators.
Run it together
Run JavaScript, TypeScript, or Python right in the browser. The output is shared with the whole room.
Keyboard-first
⌘K for every action, ⌘↵ to run. Your hands never leave the keys.
One link to join
Send a link. They sign in, and they're in the room. No installs, no setup.
Games
Take a break. Play with friends.
Nine quick games for people who code. Play solo in seconds, with no account needed, or share a code and play together, live.
Code Racer
Race to type real code.
Type a real snippet as fast as you can, against friends or three computer racers. Every key counts.
Keyword
Guess the programming word in six tries.
Every guess colors its letters: green is right, yellow is in the word somewhere. Race friends on the same words, or play today's daily.
Bit Flip
Flip bits to hit the number. Fast.
A number appears; switch the eight bits on and off until they add up to it. How many can you hit before time runs out?
Output Oracle
What does this code print?
Read a short snippet and pick what it prints before the clock runs out. Faster right answers score more.
Big-O Blitz
Name the complexity before time runs out.
Constant, logarithmic, linear… Look at the code and call its time complexity. Quick and right wins.
Bug Hunt
Find the line with the bug.
Every snippet has exactly one bug. Click the line it's on, then see the fix.
Four in a Row
Drop discs. Connect four.
Take turns dropping discs into the grid. Four of yours in a line, any direction, wins. Play a friend or the computer.
Pair Programming
Match coding concepts from memory.
Flip two cards at a time to find matching pairs, like LIFO and Stack. With friends, take turns: a match means you go again.
Byte Snake
Eat bytes, grow long, don't crash.
Steer a neon snake around the grid eating bytes. With friends, everyone plays the same board at once and sees each other live.
How it works
From zero to pairing in three steps.
Create a room
Name it and pick a language. It takes about five seconds.
Share the link
Anyone with the link can sign in and join, straight from their browser.
Build together
Edit, chat, and run code live, with everyone looking at the same thing.