The Practice Area
Reading about code and writing code are different skills, and only one of them makes you a programmer. Pick a challenge, write your solution, and press Run. HTML and JavaScript run right here in your browser — nothing goes to a server.
Ask Ada — a clue first, the full answer only if you ask.
Press Run and your output appears here.
Python is not executed on Semicolon's server. Write a solution here, then Ask Ada for a hint, a review, or (only if you want it) the solution. Run it later in Lesson 1's interpreter.
console output from your page appears here
console output appears here
Three save slots, kept in this browser only. Nothing is uploaded, so nothing can be lost by us — but clearing your browser data clears these too. Press Download .html to take a real file away with you: one file, everything inside it, opens anywhere.
How this works, and what it can't do
Everything here runs inside your own browser, on your own machine. Nothing is uploaded and no server is involved. That is why it is instant and free.
The live preview is a real web page rendered in an <iframe> — the same technology every code-preview site uses. It is sandboxed, so code you write there cannot reach out and change this page around it.
Why JavaScript and not Python? Every browser already contains a JavaScript engine. None contains Python. Running Python needs Python installed on your computer, which is exactly what Lesson 1 walks you through. The good news: loops, variables and conditions work the same way in both, so what you practise here transfers.
And a real hosted site? That is a different step, and a free one — Getting it online covers it. Download your page here, drag the file onto a free host, and it has a real address anyone can open.