Free and open source

Learn to code, one clear step at a time.

Short lessons with examples you can run and change right in your browser. Practise with exercises that check your answer. No account, no installs, no paywall.

Start with Python Browse all courses
  • 32 courses
  • 330 lessons
  • 135 checked exercises

New to programming? Start here.

Pick one course and follow it in order. Each lesson takes about 10 to 20 minutes.

Try it now

This is what every lesson looks like: real code you can edit and run. Python loads the first time you press Run, which takes a few seconds.

# This is real Python, running in your browser.
# Change the list, then press Run (or Ctrl+Enter).
groceries = ["apples", "bread", "milk", "apples", "eggs", "milk", "apples"]

counts = {}
for item in groceries:
    counts[item] = counts.get(item, 0) + 1

for item, n in sorted(counts.items(), key=lambda pair: -pair[1]):
    print(f"{item:<7} {'#' * n} {n}")
Python (loads on first run)Ctrl+Enter runs
Output
Press Run (or Ctrl+Enter) to execute this code in your browser.

How the lessons work

Every lesson follows the same simple pattern, so you always know what comes next. More about the approach

  1. 1

    Read and run

    A short explanation, then an example you can run and change. Underlined words open a quick definition.

  2. 2

    Clear up common mix-ups

    Each lesson answers the question beginners most often get wrong, with the reasoning spelled out.

  3. 3

    Practise and check

    Exercises tell you which part passed and which did not. Hints and a solution are there if you get stuck.

All courses

Grouped by what they are for. Beginners: pick one from the first row.

Good first languages Friendly languages to learn programming with.

Python

Beginner

A readable, general-purpose language for scripts, data and the web.

34 lessons · 47 exercises

JavaScript

Beginner

The programming language of the web, used in browsers and on servers.

18 lessons · 23 exercises

TypeScript

Intermediate

JavaScript with types, for catching mistakes before your code runs.

13 lessons · 8 exercises

Ruby

Beginner

A readable, object-oriented scripting language, best known for web apps built with Rails.

11 lessons

Lua

Beginner

A small, simple scripting language used in games, mods and apps.

8 lessons

Build for the web Pages, styles, front-end frameworks and servers.

HTML

Beginner

The markup language that gives every web page its structure.

8 lessons

CSS

Beginner

The style sheet language that controls how web pages look.

9 lessons

Tailwind CSS

Beginner

A CSS framework built from small utility classes you apply directly in your HTML.

8 lessons

React

Intermediate

A JavaScript library for building user interfaces from components.

12 lessons

Vue

Intermediate

An approachable JavaScript framework for building web interfaces.

7 lessons

Vite

Intermediate

A fast development server and build tool for front-end projects.

6 lessons

Node.js

Intermediate

A runtime for running JavaScript outside the browser, on servers and in tools.

7 lessons

PHP

Beginner

A server-side language for building websites and web apps.

8 lessons

Data and everyday tools Databases, version control and the command line.

SQL

Beginner

The standard language for querying and changing data in relational databases.

12 lessons · 15 exercises

Git

Beginner

A version control tool that records the history of your project.

8 lessons

How the Terminal Works

Beginner

How the terminal and shell work, and what happens when you run a command.

7 lessons · 5 exercises

Bash

Beginner

The standard shell on Linux and macOS, used for commands and scripts.

8 lessons · 3 exercises

PowerShell

Beginner

Microsoft's cross-platform shell for automating Windows, Linux and macOS.

8 lessons

Apps and systems languages Compiled languages for apps, services and performance.

Go

Intermediate

A small, fast, compiled language for servers, command-line tools and cloud services.

12 lessons

Rust

Advanced

A fast systems language that prevents memory bugs at compile time.

12 lessons

Java

Intermediate

A statically typed, object-oriented language for Android apps and large backend systems.

13 lessons

Kotlin

Intermediate

A concise, modern language for Android apps that runs on the JVM.

8 lessons

Swift

Intermediate

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

8 lessons

C#

Intermediate

A modern, typed language from Microsoft for apps, games and web services on .NET.

13 lessons

C++

Advanced

A fast, compiled language that builds on C with classes, templates and a large standard library.

13 lessons

C

Intermediate

A small, fast systems language that shows you how computers really work.

12 lessons

How computers work The ideas underneath every program.

Data Structures & Algorithms

Intermediate

Common ways to organise data and solve problems efficiently.

9 lessons

How the Internet Works

Beginner

What happens between typing a URL and seeing the page.

7 lessons

Computer Architecture

Advanced

How the hardware runs your code.

7 lessons

Operating Systems

Advanced

The software that manages the hardware and runs your programs.

7 lessons

Compilers

Advanced

How source code is turned into a program the computer can run.

7 lessons

Assembly

Advanced

The human-readable form of the instructions a CPU actually runs.

10 lessons