Stack QuestJoin the beta

14 courses, from your first line of code to running AI in production.

Start anywhere and switch whenever you like — progress is kept per course, and a placement test lets you test out of an accessible unit you already know. The opening units are free; later units require Full Access. Runnable exercises use JavaScript. Python, SQL, Git, Web, DevOps and Security use other exercise types.

Courses
14
Units
108
Sessions
589
Exercises
8,060

JavaScript

The language itself, from values to async

Learn the language: values, functions, arrays, objects, control flow, strings, asynchrony and modern syntax. Read, predict and write it, with runnable drills. When you want to apply it to real service components, Service code picks up where this leaves off.

Units
8 units
Sessions
40 sessions
Skills tracked
32 skills tracked
Exercises
554 exercises
Estimated time
≈3h of sessions

Units

  1. 1Values and variables
  2. 2Functions and scope
  3. 3Arrays and iteration
  4. 4Objects and JSON
  5. 5Control flow and truthiness
  6. 6Strings and text
  7. 7Asynchrony
  8. 8Errors and modern syntax

Python

Read and write real Python

Eight units from your first print() to handling errors: variables, decisions, loops, lists, dictionaries, functions, strings and exceptions. Every exercise is real Python you predict, arrange, complete or debug on your phone.

Units
8 units
Sessions
40 sessions
Skills tracked
32 skills tracked
Exercises
592 exercises
Estimated time
≈3h of sessions

Units

  1. 1Hello, Python
  2. 2Making decisions
  3. 3Repeating
  4. 4Collections
  5. 5Dictionaries and sets
  6. 6Functions
  7. 7Strings for real
  8. 8Errors

Data Structures & Algorithms

Think in structures, reason about cost

Trace arrays, maps, stacks, lists, recursion, trees and graphs on concrete inputs, count what they cost, then build each one in JavaScript.

Units
8 units
Sessions
40 sessions
Skills tracked
31 skills tracked
Exercises
474 exercises
Estimated time
≈3h of sessions

Units

  1. 1Big-O by feel
  2. 2Arrays and strings
  3. 3Hash maps and sets
  4. 4Stacks and queues
  5. 5Linked lists
  6. 6Recursion
  7. 7Trees
  8. 8Graphs

Databases & SQL

Ask data the right questions

Six units from a single table to query plans: tables and rows, SELECT and WHERE, JOINs, GROUP BY and aggregates, indexes and plans, transactions and schema design. Every exercise is a real query you run in your head against rows on the screen.

Units
6 units
Sessions
30 sessions
Skills tracked
24 skills tracked
Exercises
360 exercises
Estimated time
≈2h of sessions

Units

  1. 1Tables and rows
  2. 2SELECT and WHERE
  3. 3JOINs
  4. 4GROUP BY and aggregates
  5. 5Indexes and query plans
  6. 6Transactions and schema design

Web & APIs

How the web actually talks

Six units from a single request to a retry budget: HTTP by hand, designing an API, JSON payloads, identity, the browser side, and what to do when it goes wrong. Every exercise puts a real request or response on the screen and asks what comes back.

Units
6 units
Sessions
30 sessions
Skills tracked
24 skills tracked
Exercises
384 exercises
Estimated time
≈2h of sessions

Units

  1. 1HTTP by hand
  2. 2Designing an API
  3. 3JSON and payloads
  4. 4Identity on the web
  5. 5The browser side
  6. 6When it goes wrong

Git & collaboration

Work with other people without fear

Five units from your first commit to rescuing work you thought was gone: the staging area, branches as pointers, merging and rebasing, a shared remote, and the undo commands. Every exercise starts from a history sketch or a git status you can read on the screen.

Units
5 units
Sessions
25 sessions
Skills tracked
20 skills tracked
Exercises
320 exercises
Estimated time
≈2h of sessions

Units

  1. 1Commits and history
  2. 2Branching
  3. 3Merging and rebasing
  4. 4Working with a remote
  5. 5Undoing things

TypeScript

JavaScript that tells you when you are wrong

Add types to the JavaScript you already write: annotations and inference, interfaces, unions and narrowing, function signatures, generics, and the utility types that make real code readable. Every session is tap-to-answer, with runnable drills.

Units
6 units
Sessions
30 sessions
Skills tracked
24 skills tracked
Exercises
416 exercises
Estimated time
≈3h of sessions

Units

  1. 1Types and inference
  2. 2Objects and interfaces
  3. 3Unions and narrowing
  4. 4Typing functions
  5. 5Generics
  6. 6Typing real code

Service code

The code behind the systems you design

Write the components a real service is made of: the functions behind an endpoint, batching, API boundaries that hold, traffic control, safe state changes and a job worker that survives retries. Every exercise runs against executable tests. This is applied JavaScript — if the language itself is new, start with the JavaScript course.

Units
6 units
Sessions
25 sessions
Skills tracked
25 skills tracked
Exercises
438 exercises
Estimated time
≈4h of sessions

Units

  1. 1Functions behind a service
  2. 2Collections and batching
  3. 3Reliable API boundaries
  4. 4Control traffic
  5. 5Make state changes safe
  6. 6Build a resilient job worker

System design

Build systems that scale

From your first request to distributed storage, resilient services, and complete system designs.

Units
12 units
Sessions
77 sessions
Skills tracked
65 skills tracked
Exercises
1,117 exercises
Estimated time
≈8h of sessions

Units

  1. 1Your first system
  2. 2Reason about performance
  3. 3Store data correctly
  4. 4Data at scale
  5. 5Make reads fast
  6. 6Connect services
  7. 7Asynchronous systems
  8. 8Keep services running
  9. 9Ship and operate
  10. 10Protect the system
  11. 11Design complete services
  12. 12Learn from real systems

Generative AI

From LLMs to agent systems

Understand models, build retrieval and agent systems, evaluate behavior, and operate AI in production.

Units
14 units
Sessions
90 sessions
Skills tracked
76 skills tracked
Exercises
1,216 exercises
Estimated time
≈9h of sessions

Units

  1. 1Understand language models
  2. 2Prompts, conversations, and tools
  3. 3Build with retrieval
  4. 4Build agent systems
  5. 5Serve models efficiently
  6. 6Adapt models to a task
  7. 7Vision and generation
  8. 8Build multimodal systems
  9. 9Documents and data quality
  10. 10Measure model behavior
  11. 11Test reasoning and knowledge
  12. 12Safety and robustness
  13. 13Operate AI products
  14. 14Design AI applications

Machine learning

From data to production

Frame an ML problem, build data and training pipelines, serve models, and keep them reliable.

Units
11 units
Sessions
72 sessions
Skills tracked
61 skills tracked
Exercises
1,041 exercises
Estimated time
≈7h of sessions

Units

  1. 1Frame the learning problem
  2. 2Build the data foundation
  3. 3Curate training data
  4. 4Train and explain models
  5. 5Evaluate beyond one score
  6. 6Make models efficient
  7. 7Operate a changing model
  8. 8Scale training and inference
  9. 9Perception, language, and search
  10. 10ML in the real world
  11. 11Explore advanced architectures

DevOps & Cloud

Ship it, run it, know when it breaks

Six units from a Dockerfile to a cloud bill: what an image really is, what a pipeline runs and when, where configuration and secrets belong, how a deploy goes forward and back, which signal answers which question, and what you are actually paying for. Every exercise puts a real file, command or rollout on the screen and asks what happens.

Units
6 units
Sessions
30 sessions
Skills tracked
24 skills tracked
Exercises
384 exercises
Estimated time
≈2h of sessions

Units

  1. 1Containers
  2. 2CI/CD
  3. 3Configuration and secrets
  4. 4Deploying safely
  5. 5Knowing what happened
  6. 6Cloud building blocks

Security

Think like the person attacking your code

Six units on the weaknesses that put real applications on the front page: input that turns into code, passwords stored the wrong way, an ownership check nobody wrote, a script that runs in someone else's session, a key in the repository, and a dependency you never chose. Every exercise puts your own code on the screen and asks what is wrong with it and how to fix it.

Units
6 units
Sessions
30 sessions
Skills tracked
24 skills tracked
Exercises
384 exercises
Estimated time
≈2h of sessions

Units

  1. 1Untrusted input
  2. 2Authentication
  3. 3Authorization
  4. 4Browser attacks
  5. 5Secrets and crypto
  6. 6Dependencies and the supply chain

Testing & craft

Code you can change without fear

Write tests that can fail for the right reason, choose the cases that matter, isolate what you cannot control, keep a suite you can live with, refactor safely, and review code like someone who has to maintain it. JavaScript throughout, tap-to-answer with runnable drills.

Units
6 units
Sessions
30 sessions
Skills tracked
24 skills tracked
Exercises
380 exercises
Estimated time
≈2h of sessions

Units

  1. 1What a test is
  2. 2Choosing cases
  3. 3Isolating code
  4. 4Tests you can live with
  5. 5Changing code safely
  6. 6Craft

Every title, count and colour on this page is read at build time from the curriculum file the app itself downloads — content build 2026.09.30.9, made . Nothing here is typed by hand, so it cannot quote a course the app does not ship.

Content adapted from SystemDesigner (systemdesigner.net), CC BY-SA 4.0; code MIT.

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