Is this really running code, or a simulated console?

Real code. Python runs on CPython compiled to WebAssembly, JavaScript on your browser's own engine, TypeScript through the real TypeScript compiler, Java through the real OpenJDK javac, C++ and C through a real clang toolchain, C# through Roslyn and Mono's WebAssembly runtime, Go through the yaegi interpreter, Ruby through CRuby, PHP through php-wasm, R through webR, Bash through a simulated shell, and SQL on real SQLite — all inside a sandbox in your browser. HTML and CSS are rendered by your browser itself, in a locked-down preview. A language is listed as running here only after real code has been run in it through that sandbox and every check passed.

Does my code get sent to a server?

No. There is no server-side code execution on this site at all. Everything runs locally in your browser, in a sandbox whose browser-enforced security policy blocks requests to any other website. Your progress is saved in your browser's own storage and never uploaded.

Do I need an account to use the coding exercises?

No account exists to create. Every exercise, lesson, playground and practice problem is free, and your finished exercises, solved problems and streak are stored in this browser only. The progress page lets you export them as a file and import them elsewhere.

Which languages can I run here right now?

Thirteen languages run in the browser — Python, JavaScript, TypeScript, Java, C++, C, C#, Go, PHP, Ruby, R, SQL and Bash — and HTML and CSS have a live preview. Twelve of those have a free exercise path and a practice hub already (C# is next), and every one of them has a playground. The other language pages — Rust, Kotlin, Swift and Dart — are written guides with a first program and instructions for running the language on your own computer, and each says plainly that it does not run here.

How are the practice problems graded?

Your program is executed against sample tests and then against hidden tests, and its printed output is compared with the expected output. Your source code is never compared as text, so any correct approach passes and a memorised answer does not.

Python, JavaScript, TypeScript, Java, C++, C, C#, Go, PHP, Ruby, SQL, R and Bash & the Shell · Free · No account

Learn to code by writing, running and fixing real code

Most sites hand you a video and hope it sticks. Here you write code on the first screen, run it in your browser, and see something appear — a banner, a countdown, a receipt. Each exercise path takes you from your first line to a finished program, and nothing you write is ever sent to a server.

Start the first Python exercise Open a playground

130 free exercises across 13 languages
24 graded practice problems
43 in-depth lessons
19 programming terms explained

Exercise 5: Countdown

Python

print("========================")
print("    LAUNCH SEQUENCE")
print("========================")

for n in range(5, 0, -1):
    print("   T minus", n)

print("========================")
print("        LIFTOFF")
print("========================")
print("           ^")
print("          | |")
print("         (| |)")
print("          ***")

Output

========================
    LAUNCH SEQUENCE
========================
   T minus 5
   T minus 4
   T minus 3
   T minus 2
   T minus 1
========================
        LIFTOFF
========================
           ^
          | |
         (| |)
          ***

Runs in your browser

Pick a language and start

Each of these runs inside your own browser: Python on real CPython, compiled to WebAssembly; JavaScript on your browser's own JavaScript engine; TypeScript on the real TypeScript compiler, so types are genuinely checked; Java on the real OpenJDK javac, itself running as WebAssembly; C++ on a real clang toolchain, itself running as WebAssembly; C on the same clang toolchain, compiling C; C# on Roslyn compiling real C# to .NET IL, run by Mono's WebAssembly runtime; Go on yaegi, a real Go interpreter compiled to WebAssembly; PHP on real PHP 8, compiled to WebAssembly; Ruby on real CRuby, compiled to WebAssembly by the ruby.wasm project; SQL on real SQLite, compiled to WebAssembly; HTML & CSS on your browser's own rendering engine, in a locked-down preview frame; R on the real R interpreter, compiled to WebAssembly by webR; Bash & the Shell on a simulated shell that understands real bash syntax and coreutils. A language that runs in the sandbox is listed only after real code has been run in it and every check passed.

Python

Runs here

The most readable first language, and the one data and AI work is written in.

10-exercise path
9 lessons
Playground
Cheat sheet
24 graded problems

JavaScript

Runs here

The language every browser runs, and with Node, most servers too.

10-exercise path
9 lessons
Playground
Cheat sheet
3 graded problems

TypeScript

Runs here

JavaScript with a type checker that catches mistakes before the code runs.

10-exercise path
9 lessons
Playground
Cheat sheet

Java

Runs here

A strict, compiled language behind Android apps and much of enterprise software.

10-exercise path
Playground

C++

Runs here

Fast, close to the hardware, and the language of games, engines and browsers.

10-exercise path
Playground

C

Runs here

The small language operating systems are written in, and where memory is yours to manage.

10-exercise path
8 lessons
Playground
Cheat sheet

C#

Runs here

Microsoft's general-purpose language, used for Windows software, web backends and Unity games.

10-exercise path
Playground

Go

Runs here

A simple compiled language built for servers, tools and cloud infrastructure.

10-exercise path
Playground

PHP

Runs here

The server-side language behind a large share of the web, including WordPress.

10-exercise path
Playground

Ruby

Runs here

An expressive language known for the Rails web framework and readable code.

10-exercise path
Playground

SQL

Runs here

The language for asking questions of a database, used in almost every technical job.

10-exercise path
8 lessons
Playground
Cheat sheet

HTML & CSS

Live preview

The structure and styling of every web page; the first thing a web developer learns.

Playground

R

Runs here

A language built for statistics and data analysis, with plotting and modelling at its core.

10-exercise path
Playground

Bash & the Shell

Runs here

Automating a computer from the command line: scripts, pipes, and the glue of every server.

10-exercise path
Playground

Start here

The free exercise paths

In order, each teaching one idea, each ending with something you can look at. No account, nothing to install. You can finish the first one in about a minute.

Beyond the first steps

Lessons, practice, tools and a place to experiment

Lessons

In-depth written lessons with examples that were executed before publishing. Read the idea, run the code, then practise it.

43 lessons →

Practice problems

Interview-style problems graded against hidden test cases, not just the examples you can see — so a hard-coded answer does not pass.

24 problems →

Playgrounds

An editor and a Run button, nothing in the way. Try an idea in any of the 14 languages that run here.

Open a playground →

Cheat sheets

Fast-scanning syntax references, one per language, for the moment you remember an idea but not its exact shape.

5 cheat sheets →

DSA Visualizers

Watch sorting, binary search, linked lists, stacks, recursion and graph traversal run one step at a time — play, pause, and step through it yourself.

6 visualizers →

Developer tools

Format JSON, decode a JWT, test a regular expression, hash a string or convert a timestamp. Each one runs in your browser, with nothing uploaded.

10 tools →

Git commands

The commands that cover everyday version control, grouped by what you are trying to do, each with examples and a warning wherever one can lose work.

55 commands →

Linux commands

Files, text processing, pipes, permissions, processes and networking from the shell, with the macOS differences noted where they matter.

73 commands →

Build

Projects, and a route through all of it

Exercises teach one idea at a time; a project makes you combine them. A roadmap puts both in order for the kind of work you want to do.

Project briefs

What to build, the requirements that define done, milestones in a sensible order, hints, and how to test it yourself. Several can be built in a playground here.

12 projects →

Career roadmaps

Frontend, backend, full-stack, data, AI, DevOps, SAP and interview preparation — each an ordered route through the pages here, plus what you will need to learn elsewhere.

8 roadmaps →

Beyond the code

Interview prep and the concepts behind it all

Writing code is one skill; explaining how the web, databases, and the systems around your code actually work is another — and it's what technical interviews spend most of their time on.

Interview Prep

Original coding/DSA, SQL, frontend, backend, database, system design, DevOps/cloud, AI/ML and behavioral questions — each with a full explanation or model answer, plus a shuffled mock-interview mode.

Start practicing →

Concept Guides

Programming fundamentals, data structures, web & backend systems, databases, Git/Linux/ DevOps, security, AI/ML for developers, and SAP & enterprise systems — the ideas behind the code, in plain English.

Browse the guides →

Language guides

Deciding what to learn next

Plain-English guides to the languages people most often ask about: what each one is for, a first program, how to run it on your own computer, a learning order, and the honest trade-offs. These languages do not run in the browser here yet — each guide says so, and shows the real way to run them locally.

Rust

Guide

Systems-level speed with a compiler that refuses whole classes of memory bugs.

Kotlin

Guide

The modern language for Android, fully interoperable with Java.

Swift

Guide

Apple's language for iPhone, iPad and Mac apps.

Dart

Guide

The language behind Flutter, for building mobile, desktop and web apps from one codebase.

How this works

Real code, running privately

Not a simulator

Python, JavaScript, TypeScript, Java, C++, C, C#, Go, PHP, Ruby, SQL, R and Bash & the Shell all execute real runtimes in a sandbox inside your own browser. The errors you see are the language's own, not paraphrased.

Your code stays on your device

There is no server-side execution at all. The sandbox's security policy blocks every request to any other website, and your progress lives in your browser's own storage. How the sandbox works.

Progress without an account

Finished exercises, solved problems and your daily streak are saved in this browser. Export them as a file to move to another one. See your progress.

Questions people ask before starting

Is this really running code, or a simulated console?: Real code. Python runs on CPython compiled to WebAssembly, JavaScript on your browser's own engine, TypeScript through the real TypeScript compiler, Java through the real OpenJDK javac, C++ and C through a real clang toolchain, C# through Roslyn and Mono's WebAssembly runtime, Go through the yaegi interpreter, Ruby through CRuby, PHP through php-wasm, R through webR, Bash through a simulated shell, and SQL on real SQLite — all inside a sandbox in your browser. HTML and CSS are rendered by your browser itself, in a locked-down preview. A language is listed as running here only after real code has been run in it through that sandbox and every check passed.
Does my code get sent to a server?: No. There is no server-side code execution on this site at all. Everything runs locally in your browser, in a sandbox whose browser-enforced security policy blocks requests to any other website. Your progress is saved in your browser's own storage and never uploaded.
Do I need an account to use the coding exercises?: No account exists to create. Every exercise, lesson, playground and practice problem is free, and your finished exercises, solved problems and streak are stored in this browser only. The progress page lets you export them as a file and import them elsewhere.
Which languages can I run here right now?: Thirteen languages run in the browser — Python, JavaScript, TypeScript, Java, C++, C, C#, Go, PHP, Ruby, R, SQL and Bash — and HTML and CSS have a live preview. Twelve of those have a free exercise path and a practice hub already (C# is next), and every one of them has a playground. The other language pages — Rust, Kotlin, Swift and Dart — are written guides with a first program and instructions for running the language on your own computer, and each says plainly that it does not run here.
How are the practice problems graded?: Your program is executed against sample tests and then against hidden tests, and its printed output is compared with the expected output. Your source code is never compared as text, so any correct approach passes and a memorised answer does not.

Also on SkillAIVibe

The other half of this site teaches AI in plain English. If you want to understand the tools you will be coding alongside, the AI courses, the Agentic AI hub and the Cursor vs GitHub Copilot comparison are written for exactly that. The glossary now covers programming terms as well as AI ones.