Online Playgrounds & Compilers

Write, run and share C# and .NET code in the browser. Instead of installing Visual Studio you try a small snippet at once — the .NET counterpart to JSFiddle.

A browser playground for HTML, CSS and JavaScript. Unlike JSFiddle its real value is discovery — you learn by taking apart other people’s CSS tricks.

A collaborative editor for technical interviews with live coding (many languages). Unlike simple shared editors such as CodeShare, it runs the code and can replay the session step by step afterwards.

Runs projects with full npm dependencies in the browser. Unlike CodePen it opens a real React or Node project as-is.

Real-time collaborative code editing in the browser with no install or account. Compared with CoderPad it does not run code, but it opens instantly — a fast option for remote pairing or an interview.

Puts the generated assembly beside your source, with optimisation level and compiler version switchable so you see the difference immediately. It moves performance arguments from opinion to measurement.

Compiles and runs 60+ languages in the browser and accepts an input stream. Unlike project environments such as Replit it is light, for single files — trying a language’s syntax without installing anything.

A JSFiddle-like scratchpad with a live output panel; showing console output on the same screen is handy when debugging.

The oldest and lightest way to test a small JavaScript snippet. Unlike CodePen it is about reproducible examples rather than discovery — the standard tool for attaching one to a bug report.

An open-source online compiler. Unlike closed services such as Ideone you can self-host its engine — the project people building code assessment systems use as infrastructure.

An in-browser playground to try HTML, CSS and JS with live preview. Unlike CodePen it is a plain, account-free scratchpad without the community and discovery layer.

An online IDE supporting many languages, with no install. Unlike Replit you can run and share single-file code by link without an account; the trade-off is limited multi-file project support.

Starting as the Gitpod cloud dev environment, it became Ona in 2025 — a platform for background AI coding agents. Unlike cloud environments such as GitHub Codespaces, it now centres on the agents running inside rather than the environment itself.

An experimental tool that converts code written in one language into others — C#, Java, Python, JavaScript. Against a syntax comparison table it produces working translations, which shows how one language’s idiom lands in another.

An online IDE that compiles C and many other languages in the browser. Unlike run-only sites such as Ideone it includes the gdb debugger, so you can set breakpoints and step through.

A JavaScript and TypeScript playground that runs as you type and accepts npm packages. Against CodePen the feedback is instant and the console always visible; against CodeSandbox it is lighter for trying a library.

A collaborative cloud IDE that writes and runs dozens of languages in the browser and can deploy a project in one click. Unlike snippet playgrounds such as JSFiddle, it runs whole projects with a filesystem, package installs and hosting.

A JavaScript playground that evaluates as you type. Unlike the browser console it shows each line’s value alongside without a console.log.

Runs Node.js in the browser through WebContainers. Unlike online IDEs that spin up server-side containers, install and restart are instant — it even works offline.

Runs dozens of C++ compiler versions side by side. Unlike Compiler Explorer it shows the program’s run output rather than the assembly — for testing which standard or compiler release a behaviour comes from.