Repl from Repo

Amjad Masad

When I think of GitHub I imagine a vast network of people and code; a superorganism that changed how we make software. When I was getting into programming, starting a new project was daunting -- you had to imagine and build everything nearly from scratch. My version of code-sharing was calling my older cousin who was going to college for CS and getting code dictated to me over the phone. When the Internet arrived in my home town, it made hacking on new projects so much more fun. Starting a new project, at least initially, became about discovery:

  • I would walk to the Internet cafe and Yahoo search “vb code online”
  • There were a number of pseudo-GitHub sites that hosted Visual Basic projects
  • I’d download projects related to what I wanted to build, burn them on a CD and head back home
  • I’d run these projects, change & tinker with them, and get inspired on how to build my own

This mirrors the experience of many developers today, except, thanks to GitHub, they have many more options and a lot smoother UX. However, one thing that has remained the same: You still have to download projects you discover on GitHub and figure out how to run them just to start tinkering. While easier than walking to the Internet cafe, it’s enough friction that many people will give up.

That’s why today we’re making it easier to run repos on Now you can instantly run code from a GitHub repository without the hassle of configuring a local development environment. Simply click the import button on or click a run on badge, which will be coming to README files near you.

Here’s how it works

After cloning a GitHub repo into a repl we detect the run command, and if we’re unable to do so we help the user configure a .replit file that includes the run command information. We then help the user create a Pull Request back to GitHub so that other users won’t have to search for the run command in the future.

How is it possible?

At we built multiple layers of abstractions in pursuit of minimum configuration instant programming environments:

  • Polygott: This is our base monster docker image that we hope includes most of the native dependencies necessary to run most projects (we’re also aiming to make this image swappable with your own in the future)
  • UPM is our universal package manager that knows how to install packages in a number of different programming languages we support.
  • Window manager: Our novel approach to window management allows us to reconfigure the IDE on the fly to create any number of environments: from web apps to command line or even data science environments.
  • Collaborative Development Protocol (crosis): Makes it possible for us to operate Git from the browser. It’s as simple as opening an exec channel and streaming git commands to the server.
  • Distributed filesystem: A snapshot-based filesystem with atomic writes is necessary when dealing with large-scale file changes which happens when running git.

This is all work in progress and doesn’t give us anywhere near 100% coverage on all GitHub repos, however, all the essential components are there and it’s a matter of improving our infrastructure to cover more and more projects that can be instantly run in the browser.

As much as possible, we're building our infrastructure in the open, and with participation from our community. If we don't support your favorite language or runtime, please consider contributing to Polygott and UPM.

Try it out

This feature was silently earlier this week to our community, and since then we’ve seen a lot of excitement from both our users and repo authors when they receive a pull-request. Here are some of our favorites so far. Just go to the repo and click “run on” to see it in action.

  • ascii_racer is a python race game in the terminal; it’s super fun.
  • Minesweeper is a Minesweeper in C++
  • ddgr: search DuckDuckGo from your terminal
  • pycraft: 2D minecraft in Python!
  • legit: Human-friendly git utility
  • progress-bot: a discord/slack bot to report your anime progress on the web.
  • water.css: a super simple CSS framework.
  • snake-go: a snake implementation in go.

If you’d like to add it to your repo, simply import a repo and follow the prompts. I also wrote a quick guide here.

If you have any trouble getting your repo to work, consider asking a question on our community, or visit the #developers channel on our Discord server.

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