Run something now

Each language has its own page. Open it, replace what is there, run it. Nothing is installed and nothing is left behind on your machine.

Versions matter more than people expect

Every language offers several versions, and you choose which one runs. That turns a common argument into a two-minute check: run the same code on two versions and see whether the behaviour you are arguing about is actually a version difference.

It is also the honest way to reproduce a bug report. Matching the version the reporter used is usually the difference between seeing their problem and telling them it works fine.

Giving it input

• Input

  Fixed text your program reads when it runs. Set it once and re-run against the same input while you change the code.

  Good for reproducing something repeatedly.

• Interactive

  Answer the program as it asks, the way a terminal would.

  Good for anything that prompts, and for seeing what a user would see.

What this path does not give you

A single run is stateless. Nothing persists between runs, there is no shell, and a program that expects to be a long-running service has nowhere to run.

Those need an environment, which is a different thing on a different page.

What next

When one file stops being enough, or the code needs a library, the project side of the editor is where that happens.

If the code you want to run is usually something you found while reading, the browser extension runs it without leaving the page.