Free · No account · Runs in your browser

Actually learn
to code.

AI can write code. Someone still has to understand it. Short lessons, a real editor on every page and exercises that check your work. You type every line, so it ends up in your head and not just in a chat window.

Pick a track Start with Python

51 lessons · 103 checked exercises · Python, JavaScript, HTML/CSS, SQL and C

hello.jsChange the name. Press Run.
const name = "your name";

for (let i = 3; i > 0; i--) {
  console.log(i + "...");
}
console.log("Hi " + name + ", you just ran code.");
or Ctrl/Cmd + Enter
Output appears here.

Pick a track

Each one is 12 to 14 short lessons, beginner to early intermediate. Do them in order or jump around; nobody is grading you except the checker.

py The friendly one Python Variables, loops, functions, lists and dicts. The language that reads almost like English and runs half the internet's scripts. 14 lessonsTotal beginner </> Make things people can click JavaScript + HTML/CSS Build a page with HTML, style it with CSS, then make it react with JavaScript. Everything runs right here in the page. 13 lessonsTotal beginner SQL Ask data questions SQL SELECT, WHERE, JOIN, GROUP BY. Query real tables in your browser and learn how apps actually remember things. 12 lessonsBeginner C How computers actually work C Memory, pointers, the stack, malloc. The language under your operating system, compiled for real in your browser. 12 lessonsSome coding helps

The pitch

Why learn it yourself when a chatbot can write it?

Because someone has to spot the bug

AI writes code that looks right and is quietly wrong. If you cannot read it, you cannot tell. Learning the basics is how you stop being the person who pastes and prays.

Typing is how it sticks

Reading a solution feels like learning. It mostly is not. Your fingers making the mistake, then fixing it, is what builds the mental model. So the exercises start nearly empty.

Errors are the curriculum

Every red message in the output is a lesson nobody had to write. You will see a lot of them here, on purpose, with hints that nudge instead of spoil.

Then use AI, properly

Once you understand the code, AI turns into a fast assistant instead of a crutch. You ask better questions and you know when the answer is nonsense. That is the goal.

How a lesson works

  1. 1

    Read one idea

    150 to 300 words. Plain language, no padding, one concept per page.

  2. 2

    Run the example

    It is a real editor. Change things and see what breaks. Breaking things is allowed.

  3. 3

    Solve the exercise

    Press Check. The site runs your code and tells you if it works. Hints if you are stuck.

Python runs on real CPython, C is compiled for real, SQL is real SQLite. All of it in your browser, nothing on our servers.

Then build something

Small projects that make you glue the ideas together. One per track below; more on the projects page, and bigger Pro projects are on the way.

FreePython · 30 min

Number guesser

The computer picks a number, you guess, it says higher or lower. Loops, if/else and input() in one tiny game.

  1. Pick a secret number with random.randint(1, 100).
  2. Read guesses from input() in a while loop.
  3. Print "higher" or "lower" until the guess is right, then print how many tries it took.
Start in the playground
FreeWeb · 45 min

Bill splitter

Two inputs, one button, one answer. Read values from a form, do some maths, show the result on the page.

  1. Make inputs for the bill total and the number of people.
  2. On click, read both values with Number(input.value).
  3. Show each person's share with two decimals using toFixed(2).
Start in the playground
FreeSQL · 30 min

Playlist stats

Answer real questions about a playlist: top artists, total minutes, the longest song. GROUP BY gets a workout.

  1. Count songs per artist and sort by the count.
  2. Find the total playlist length in minutes.
  3. Find the longest song with ORDER BY and LIMIT.
Start in the playground
FreeC · 40 min

Bit printer

Print any number in binary using shifts and masks. Once you can see the bits, overflow stops being magic.

  1. Write void print_bits(unsigned char x).
  2. Loop from bit 7 down to 0 and print (x >> i) & 1.
  3. Print 5, 255 and what 255 + 1 becomes in an unsigned char.
Start in the playground

All projects

Ten minutes is enough to start

Lesson 1 of every track is short, and you write real code in it. No setup, no sign-up, nothing to install.

Start Python lesson 1Just let me type code

Questions people ask

Is it actually free?

Yes. All lessons, exercises and playgrounds are free and stay free. Later we will add bigger Pro projects, which is how the free part pays for itself.

Do I need an account?

No. Your progress and your code are saved in this browser. Clear your browser data and it is gone, so that is the trade-off.

Do I need to install anything?

No. Python runs on real CPython compiled to WebAssembly, C is compiled by a real C compiler, and SQL is real SQLite, all inside your browser tab. Nothing to download or set up.

Does it work on a phone?

Yes, the lessons and editor work on phones. A laptop is nicer for longer code, because curly brackets on a phone keyboard are a crime.

Which language should I start with?

Python if you have never coded. HTML/CSS + JavaScript if you want to make websites. SQL if you like data. C if you want to know what the computer is really doing.

Can I use this for school or a coding class?

Yes. Every lesson is one idea with a runnable example and checked exercises, so it works for homework, revision or a quick in-class demo. Share the lesson link; there is nothing to sign up for.

What is Brainlag?

brainlag.space is a free site for students with study tools, guides and games. This is the coding corner of it.

Code editor. Press Control or Command plus Enter to run the code. Tab indents; to move focus out of the editor, press Escape and then Tab.