Project Catalog

Build Real Projects.
Not Toy Tutorials.

Every track is a real, test-driven build — rebuild the libraries you rely on, or ship a production app milestone by milestone.

Languages

50+

Challenges

Code Review

Two Ways to Level Up

Pick focused challenges to sharpen core skills, or build a full product the way real engineering teams do.

Fundamentals

Sharpen the Fundamentals

Focused, test-driven coding challenges that rebuild the libraries and tools you use every day — from scratch.

Test-driven coding challenges
Multiple languages & paradigms
Real-world patterns, not toy problems

Project as Product

Build Real Products

Ship production-grade applications across phases and milestones, with AI code review modeled on a real engineering workflow.

Phases, milestones & dependencies
AI-powered code review on every push
A portfolio of shippable projects

Explore the Catalog

A taste of what you'll build. Sign in to track progress, earn streaks, and unlock the full library.

Intermediate

JavaScript Core

Build Your Own Promise Library

Implement a Promises/A+ compliant library from scratch, then watch it pass the full conformance suite.

Reimplement Array Methods

Rebuild map, filter, reduce and friends from first principles — and understand iterators along the way.

arraysiteratorsfunctional

8 challenges

Advanced

TypeScript

TypeScript Type Challenges

Bend the type system to your will with conditional types, inference, and recursive generics.

genericsinferencetypes

10 challenges

Intermediate

React

Build Your Own React Hooks

Recreate useState, useEffect, and the reconciliation loop to learn how hooks really work under the hood.

hooksstaterender

6 challenges

Intermediate

Build an HTTP Server in Go

Ship a concurrent HTTP server across phases and milestones, with AI code review on every push.

httpconcurrencygo

Product · 4 milestones

Advanced

Rust

Ownership & Borrowing in Rust

Master the borrow checker by building a real program — memory safety with zero garbage collection.

memorytraitsrust

Product · 5 milestones

Intermediate

Full-Stack

Full-Stack Task Manager

Design the API, model the database, and wire the UI — a production app built milestone by milestone.

apipostgresauth

Product · 7 milestones

Intermediate

State Management

Build a Mini Redux

Implement a predictable state container with a store, reducers, and middleware from the ground up.

storereducersmiddleware

5 challenges

Advanced

Tooling

Build Your Own Test Runner

Create a CLI test runner with assertions, watch mode, and pretty diffs — the tool behind every challenge.

cliassertionstooling

5 challenges

Become the engineer AI can't replace.

AI isn't going away. The developers who thrive are the ones who can still think without it. Start building that edge today.

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Build Real Projects.Not Toy Tutorials.

Two Ways to Level Up

Sharpen the Fundamentals

Build Real Products

Explore the Catalog

Build Your Own Promise Library

Reimplement Array Methods

TypeScript Type Challenges

Build Your Own React Hooks

Build an HTTP Server in Go

Ownership & Borrowing in Rust

Full-Stack Task Manager

Build a Mini Redux

Build Your Own Test Runner

Become the engineer AI can't replace.

Build Real Projects.
Not Toy Tutorials.