Learn to code by
writing real code.
Short lessons, then you type every character yourself and run it in your browser — Python, SQL, JavaScript and more. No videos, no setup, no copy-paste.
# Type it yourself — paste is disabled
def sharpen(skill, reps):
for _ in range(reps):
skill += 1
return skill
print(sharpen("python", 30))Read. Type. Run.
Read a short lesson
Focused text, never a video. No lesson asks you to read for more than about ninety seconds before you do something.
Type the code yourself
Examples are shown ghosted and paste is disabled — you re-type every character. Typing builds the recall that reading never will.
Run it. Earn XP.
Your code runs on a real interpreter in the browser — no installs. Passing runs earn XP, streaks, and badges.
Start anywhere on the map
Python from Zero
From "what is code?" to building a text adventure — by typing every line yourself.
Data Structures Foundations & Complexity Analysis
Why data structure choice matters, and how to measure it — Big-O, space complexity, and reading real code for cost.
SQL from Zero
Query real databases in your browser. Tables, joins, and the questions data answers.
Generative AI Fundamentals
What makes a model generative rather than discriminative - density estimation, latent variables, the four families, autoregressive generation, decoding strategies, honest evaluation, mode collapse, and the quality/diversity trade-off. Every claim measured, not asserted.
Python Testing with Pytest
pytest's real syntax as reference — bare assertions, fixtures, parametrization, and pytest.raises reimplemented as genuinely runnable Python.
Game Development Basics & Concepts
What a game actually is under the hood — and your first playable scenes.
Then sharpen for the interview
1,100 practice problems
Interview-style Python and SQL problems with hidden tests, progressive hints, and gated solutions — Easy through Hard.
Start solving230 system design questions
ML systems, data platforms, distributed software, and low-level design — full interview walkthroughs, not outlines.
Read a design68 case studies
End-to-end data-science projects: frame the question, clean the data, model it, and defend the result.
Work a caseReady to write some code?
Everything runs in your browser and it's free to start. Your progress saves locally, or sign in to sync it across devices.