The TypeScript playground
for your desktop
A scratchpad with TypeScript built in. Live type checking, real npm, no tsconfig — all in one place.
This is one of my favorite tools
Joe PreviteDev Advocate at Facebook Open Source
Free downloadOther platforms
Explore types. Test interfaces. Try a package. Catch bugs at design time.
Sketch types as you type. Define an interface, narrow a union, see the type checker work — all without a project, a tsconfig, or a build step.
I wish I had RunJS when I was a student at Flatiron School. Awesome way to learn JavaScript and TypeScript fundamentals. Also perfect for exploring new libraries.
EdenFront End Developer
Hit any API, with types. Model the response shape, then watch TypeScript flag mistakes before the request even runs.
RunJS is a fantastic tool for prototyping and testing JavaScript and TypeScript code.
Mathew LaytonPrincipal Software Engineer
Try any npm package in seconds. Search, install, import — no project, no setup. The fastest way to evaluate a library before committing to it.
Just discovered RunJS and it's a game changer! Much better than opening VSCode, creating a test.js file and running 'node test.js'. 😅
Maxim OrlovWeb Dev and Teacher