A new way to learn code in the age of AI

Learn to read code. Let AI write it.

Learn how software works through quick, interactive challenges. Start with simple code. Work your way up to real applications.

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Try oneUnit 2 · How Code Executes

Read
Predict
Investigate
Understand
Next

Sneakers$5020% off

Total$40

The appA shop's checkout shows a pair of sneakers at $50, a 20% discount, and a total of $40.

checkout.js0/2 looked up

applyDiscount(price) {

return price * 0.8;

}

const total = ;

console.log(total);

PredictIn this code, what is price?

Tap underlined code for its meaning

Why reading

Coding changed. Learning to code should too.

AI writes the code. You inherit the problems.

69%

of developers say AI code that looked right but was wrong cost them time.

69.3% of 13,648 respondents, Stack Overflow Developer Survey 2026

AI got faster. Learning to code didn’t.

54%

say AI code that was hard to review cost them time. Traditional courses still start you on a blank file.

54.2% of 13,648 respondents, Stack Overflow Developer Survey 2026

checkout.jscart.jsapi/orders.jsutils/price.jsuseCart.jstax.js

AI writing across six files

+export async function checkout(cart, user) {
+const items = await loadItems(cart.ids);
+if (!user) return redirect('/login');
+for (const item of items) {
+if (item.stock < item.qty) {
+await notifyBackorder(item, user.email);
+item.qty = Math.min(item.qty, item.stock);
+}
+const rule = rules.find((r) => r.match(item));
+if (rule?.type === 'percent') {
+item.price = applyDiscount(item.price, rule);
+} else if (rule && user.tier !== 'basic') {
+item.price -= rule.amount ?? 0;
+if (item.price < 0) item.price = 0;
+}
+}
+const tax = await taxFor(user.region, items);
+const credit = user.credit > 0 ? user.credit : 0;
+const total = sum(items) + tax - credit;
+await saveOrder({ items, total, tax, user: user.id });
+await emptyCart(cart.id).catch(() => retry(cart));
+track('checkout', { total, n: items.length });
+return { ok: true, total, orderId: order?.id };
+}
+export async function checkout(cart, user) {
+const items = await loadItems(cart.ids);
+if (!user) return redirect('/login');
+for (const item of items) {
+if (item.stock < item.qty) {
+await notifyBackorder(item, user.email);
+item.qty = Math.min(item.qty, item.stock);
+}
+const rule = rules.find((r) => r.match(item));
+if (rule?.type === 'percent') {
+item.price = applyDiscount(item.price, rule);
+} else if (rule && user.tier !== 'basic') {
+item.price -= rule.amount ?? 0;
+if (item.price < 0) item.price = 0;
+}
+}
+const tax = await taxFor(user.region, items);
+const credit = user.credit > 0 ? user.credit : 0;
+const total = sum(items) + tax - credit;
+await saveOrder({ items, total, tax, user: user.id });
+await emptyCart(cart.id).catch(() => retry(cart));
+track('checkout', { total, n: items.length });
+return { ok: true, total, orderId: order?.id };
+}

Coding course Lesson 1: variables

let name = "Ada";

You don’t need to write every line. You need to understand what it does.

Read
Predict
Understand

Short challenges on real code train you to follow the logic, and to catch what AI gets wrong.

Join waitlist

How it works

Read. Predict. Investigate. Understand.

Every challenge runs the same quick loop: no lecture before it, no essay after. The checkout at the top of this page is one whole challenge.

01
Read
A few lines of real code. Tap any underlined expression to see what it means.
02
Predict
Commit to what you think happens. A wrong guess costs nothing and shows you where to look.
03
Investigate
Step through it. The running line lights up, values change in place, the app redraws.
04
Understand
One short why, and the pattern to spot next time. Then the same idea, in a new setting.

The curriculum

From one line to a codebase you’ve never seen.

Three tracks: Programming Fundamentals in JavaScript or Python, and Reading Typed Code in TypeScript. Each has six units and four codebase labs. Passages get longer and less familiar as you go, the way reading a new language moves from sentences to stories.

Programming Fundamentals · 6 units, 24 concepts, 4 labs. From what a single line means to finding your way around a codebase you've never seen.

Unit 1
The Language of Code
Understand what individual lines of code mean.
items.js
```
1const count = 0;2let message = "Items: " + count;3if (count) {4  message = "You have items";5}6console.log(message);
```
PrintsItems: 0
- Values and Types
- Variables and Assignment
- Expressions and Comparisons
- Boolean Logic and Conditions
Unit 2
How Code Executes
Follow a program as it runs.
checkout.js
```
1function applyDiscount(price) {2  return price * 0.8;3}45const total = applyDiscount(50);6console.log(total);
```
Prints40
- Execution Order
- Functions and Parameters
- Functions and Return Values
- Scope and Variable Lifetime

Unit 3

Understanding Data

Understand how programs organize and change information.

ratings.js

1const ratings = [4, 5, 3, 4, 2];2let good = 0;3let sum = 0;4for (const r of ratings) {5  sum = sum + r;6  if (r >= 4) {7    good = good + 1;8  }9}10console.log(good + " of " + ratings.length + ", avg " + sum / ratings.length);

Prints3 of 5, avg 3.6

Arrays and Indexing
Objects and Properties
References and Mutation
Loops and Iteration

Unit 4

How Programs Are Organized

Understand how separately defined pieces of code work together.

orders.js

1const orders = [2  { id: 1, status: "sent" },3  { id: 2, status: "pending" },4  { id: 3, status: "pending" },5];67const next = orders.find((o) => o.status === "pending");8console.log(next.id);

Prints2

Functions as Values
Callbacks and Data Transformations
Modules, Imports, and Exports
Errors and Failure Paths

Unit 5

How Applications Behave

Understand the patterns behind interactive software.

Level.jsx

1import { useState } from "react";23export default function Level() {4  const [level, setLevel] = useState(1);56  function levelUp() {7    setLevel(level + 1);8    console.log(level);9  }1011  return <button onClick={levelUp}>Level {level}</button>;12}

Click once1is logged, the button showsLevel 2

Events and Event Handlers
State and Derived Behavior
Asynchronous Code
APIs and Data Flow

Unit 6
Reading Real Codebases
Apply everything to software you've never seen.
src/index.jsdata/seed.jslib/notes.jslib/format.js
```
1import { loadNotes } from "./data/seed";2import { pinnedFirst } from "./lib/notes";3import { formatNote } from "./lib/format";45const notes = pinnedFirst(loadNotes());6for (const note of notes) {7  console.log(formatNote(note));8}
```
Prints📌 PasswordsGroceriesIdeas
- Finding the Entry Point
- Tracing a Feature
- Investigating Unexpected Behavior
- Understanding the Impact of Changes

Inside every concept

1ObserveA real behavior and a reason to care.
2UnderstandThe mental model, as a demonstration you step through.
3PredictCommit before you see. Every wrong answer explains the misreading.
4TraceFollow execution through several operations.
5ApplyUnfamiliar code, no diagram until you answer.

Each unit ends with an assessment on code you haven’t seen. A concept counts as mastered when you get its independent exercises right on the first try; finishing the lesson alone doesn’t count. Finished concepts come back for review after 1, 3, 7, 16 and 35 days, and a missed review marks a concept rusty until you get it right again.

Codebase labs

After unit 2Interactive CalculatorA four-function calculator split across four files. Follow the inputs through validation and calculation to the message the user sees.Variables · Conditions · Functions · Return values
After unit 4Shopping CartLook up products, build line totals, add them up and apply a 10% discount on orders of $40 or more.Arrays · Objects · Loops · Data transformations
After unit 5Interactive Web ApplicationA React task list across four files. Follow a click from the button to the screen.Modules · Events · State · Connected functions
After unit 5Data-Driven ApplicationThe capstone: an order-history screen that fetches, filters and totals data and handles failures, across four files.Async functions · API requests · Error handling · Multiple files

Join waitlist

Not just multiple choice

Five ways to read code.

Each kind of challenge trains a different reading skill. The first three are playable right here.

Follow the execution and watch values change.

game.js

let lives = 2;lives = 2

function gameOver() {

console.log("Game over");

}

function hit() {

lives--;

if (lives === 0) {

gameOver();

}

hit();

Step 1 of 12

Line 1. lives starts at 2.

Consolenothing printed yet

Coming later

Then, your own code.

The plan: challenges written from the project you built with AI, so you learn to read the code you actually ship. It isn’t built yet. Today’s curriculum uses challenges we write and check by hand.

api/habits/route.tsWhen you tick off a habit, where is it saved?
lib/auth.tsWhat stops someone from seeing another person’s habits?
StreakBadge.tsxWhy does your streak reset at midnight?

Fast to start. Deep enough to matter.

Join the waitlist

We’ll email you when early access opens.

Learn to read code. Let AI write it.

Coding changed. Learning to code should too.

AI writes the code. You inherit the problems.

AI got faster. Learning to code didn’t.

You don’t need to write every line. You need to understand what it does.

Read. Predict. Investigate. Understand.

Read

Predict

Investigate

Understand