Select a Language

Example Code


What is
It is an online environment for interactively exploring programming languages. The name comes from the read-eval-print loop, the interactive toplevel used by languages like Lisp and Python.
How do I start?
Once you have selected a language, start by typing an expression into the console on the right side of the screen and pressing Enter. Your expression will be evaluated in the selected language and its result will be printed. Repeat until satisfied. You can also try some ready-to-run examples by clicking on the button labeled "eg".
Can I use variables or other state?
Yes! The interpreters fully support variables, state and side effects in all the supported languages.
Can I save my session?
Yes! You can save your session and share it with others by clicking on the chain link icon in the top right corner. Both the editor's content and the REPL session will be preserved and can be executed once again using the created link to continue from where you left off.
Is open source?
Yes! You can explore the code and contribute to various parts of through our GitHub repositories.
Can I use on my phone or tablet?
Yes! As a web application, can be used on any device that has a modern web browser. Currently, we have full support for Android devices, and partial support for iOS.
How does work?
All code processed by runs entirely on your computer, with no server-side evaluation. It uses language interpreters written in JavaScript to execute your code and keep track of state. Some of the interpreters (like BiwaScheme) are originally implemented in JavaScript, while others (like Python) were compiled from their original lower-level implementations using Emscripten.
Console Shortcuts
Evaluate the entered command.
Continue to the next line.
Previous history item.
Next history item.
Move to the line above the cursor.
Move to the line below the cursor.
Move to the end of the current line.
Move to the start of the current line.
Clears the console.
Cancel current prompt.
Open languages selector.
Open examples preview.
Open this help page.
Save session (new revision).
Close current view.

About Us

The project is an attempt to create an online environment for interactively exploring programming languages. It provides a fully-featured terminal emulator and code editor, powered by interpreter engines for more than 15 languages.

All our interpreters are written in (or compiled to) JavaScript, and run completely on the user's device, regardless or whether it's a desktop, laptop or phone.

The code is open source and is available on GitHub.


Amjad MasadAmjad Masad is a software engineer at Facebook on the JavaScript infrastructure team. He lives in NYC and dabbles in improv comedy.

Max ShawabkehMax Shawabkeh is a software engineer at Google and a Python enthusiast. He fancies himself a jack of many programming trades but a master of none. He reads fantasy books and likes good food.

Haya OdehHaya Odeh is a freelance designer based in NYC. Coming from a visual design background, she can be seen obsessing over pixel perfection but also cares deeply about the user experience. She runs long distance and likes to cook food.


This application is a result of their sushi-powered collaboration.

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We are offering the code execution infrastructure that powers as service for developers to build on top of.


  • User programs run in full linux environments with access to resources
  • Persistent REPL session for interpreted languages
  • Easy to use client-side JavaScript library
  • Languages: Python 3, Ruby 2, Go 1.4, Java (request a language)
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try the API with the Hello World Example
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Browser Version Not Supported
Due to's reliance on advanced JavaScript techniques, older browsers might have problems running it correctly. Please download the latest version of your favourite browser.
Chrome 13+ Firefox 4+ Opera 11.51+
IE 10+ Safari 5+
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