A cheatsheet for each topic
Signatures and one-line explanations on one page, each linked back to its lesson.
TopicsFree, beginner-first courses
Learn it once, properly.
Every topic starts from the plain explanation and goes down to production depth. Run the code in the page, take a quiz after each section, and search to the exact line when you come back.
- Free to read, no account
- Written for a beginner first
- Run the code in the page
- AI help when you sign in
- Three levels
- Runnable code
- AI interview grading
01The topics
Pick what you want to learn.
Finished topics are complete against their outline. Topics being written are open to read now and grow section by section; the bar shows exactly how far each has come.
Python
beginner · 40+ hours
A readable, batteries-included language for backends, data work and automation.
821 of 821 outline items100%
PostgreSQL
intermediate · 15+ hours
A relational database that keeps your data correct under pressure.
132 of 428 outline items31%
System Design
advanced · 15+ hours
How to shape systems that stay fast and available as they grow.
290 of 290 outline items100%
Django
intermediate · 40+ hours
A batteries-included Python web framework for database-backed applications.
1,112 of 1,442 outline items77%
MongoDB
intermediate · 15+ hours
A document database that stores flexible, JSON-shaped records.
158 of 482 outline items33%
AWS
intermediate · 12+ hours
Rent servers, storage and managed services instead of running your own.
278 of 278 outline items100%
AI Full-Stack
advanced · 25+ hours
Ship real features on top of models — RAG, agents, evaluation and inference.
63 of 659 outline items10%
Data Structures & Algorithms
beginner · 30+ hours
Pattern-based problem solving — arrays to graphs, for interviews and daily fundamentals.
169 of 341 outline items50%
JavaScript
beginner · 30+ hours
The language every browser runs, and the foundation under React and Next.js.
0 of 866 outline items0%
React
intermediate · 12+ hours
Build user interfaces out of small, reusable pieces that react to data.
0 of 262 outline items0%
Docker
beginner · 12+ hours
Package an app with everything it needs so it runs the same everywhere.
0 of 360 outline items0%
FastAPI
intermediate · 35+ hours
Build typed, async Python APIs with validation and docs built in.
0 of 1,277 outline items0%
Next.js
advanced · 35+ hours
The React framework that handles routing, rendering and data fetching for you.
0 of 1,291 outline items0%
MySQL
intermediate · 12+ hours
The relational database behind a large share of the web.
0 of 391 outline items0%
02Learn
Every concept, taught three ways.
Explain, Example, Reference. Read the plain explanation when it is new, the worked example when you want to see it run, and the reference when you only need the shape of it again. Written for a beginner first, with depth layered underneath.
- 1.1
Code that runs in the page
Edit a Python example and run it in your browser. Nothing to install, nothing sent to a server.
- 1.2
Diagrams, not screenshots
Vector diagrams that stay sharp in print and carry a written alternative, plus a gallery of all of them.
- 1.3
Search to the exact line
One keystroke searches every concept and jumps to the anchor, not just the page it lives on.
- 1.4
Levels you can hide
Hide advanced material on the first pass and bring it back on the second.
- 1.5
Quick-reference sheets
A printable sheet per topic for the day you only need the syntax.
- 1.6
A quiz after every section
Plus patterns, common mistakes, best practices, a glossary and an FAQ.
- 1.7
Your own sources
Attach links and files to any concept and keep them beside the lesson.
03With the assistant
An assistant that has read the section.
Reading is free. When you sign in, the AI features switch on around the lesson.
AI- 01
Ask about the section you are reading
The assistant is given the section you have open: its summary, outcomes, key points and concepts. It answers in the section’s own words, and says so when your question goes further than the section does.
- 02
Interview questions, graded
Each concept has interview questions, easiest first. Type your answer and it is graded against the section’s authored rubric, not a model’s opinion. You can dispute a grade, or ask for more questions.
- 03
AI inside your notes
Select text in a note to rewrite it, simplify, summarise, explain it or turn it into bullets. For code: refactor, add comments or explain. You see a preview and choose Replace or Insert below.
- 04
Ask out loud
Speak your question into the assistant where the browser supports speech input.
- 05
It proposes, you decide
Ask it to add a topic to your plan and it shows the change first. Nothing is applied until you confirm.
AI features need a free account. Public pages are read-only.
04Around the lesson
A topic is the start, not the whole shelf.
Each topic connects to the other tools on the site, so what you read turns into something you do.
Add it to your plan
The planner dates every section and brings finished ones back for revision.
Notes beside the lesson
Write on the concept itself, and find the note again from the planner.
Diagrams with words
Vector diagrams that stay sharp in print and carry a written alternative.
?Questions
Before you start
- Are the topics free?
- Yes. Reading every topic is free and needs no account. Signing in adds the planner, notes and progress that follow you between devices.
- I am a beginner. Where do I start?
- Every concept is written for a beginner first, with the depth layered underneath. Pick a topic marked Finished, read the plain explanation, and stop there if that is enough.
- I already know the basics. Can I skip them?
- Yes. Each concept has a level, and you can hide the advanced material on a first pass and bring it back on the second. Search takes you straight to the exact line.
- Why are some topics marked as being written?
- They are written in the open, section by section. The bar on each card shows how much of the topic’s outline is covered today, so you can see what you are getting.
- How do topics connect to the rest of the site?
- Each topic has a cheatsheet for quick lookup and, for some subjects, a printable handbook. You can add any topic to your study plan and the planner dates every section.
Start with one topic. Keep going.
Reading is free and needs no account. Sign in when you want a plan, notes and progress that follow you between devices.