For students learning design
Design principles you can apply
Your textbook defines the Liskov Substitution Principle. Can you spot a violation in real code? Interactive exercises that test application, not recall.
S.O.L.I.D. through exercises
Each principle gets its own set of problems. Identify violations, refactor code, and verify with tests.
D.R.Y. in practice
Learn when duplication is a problem and when abstraction is worse. Real trade-offs, not textbook rules.
See the impact
Every exercise shows how a principle changes the code. You see the before and after, then build the solution yourself.
Beyond the acronym
Understand when to apply each principle and when to break the rules.
Write code from lesson one
Every lesson is an exercise you solve in your browser. Real code, real tests, real feedback.
Structured progression
Each concept builds on the last. You always know what to learn next.
Multiple exercise types
Quizzes, fill-in-the-blank, matching, and code keep every lesson engaging.
Instant feedback
Submit your answer and see test results in milliseconds.
Learn by doing
Solve exercises in your browser from the first lesson.
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Explore our courses
Pick a course and solve your first exercise.
Dart Course
An interactive Dart course where you code, test, and build apps directly in your browser.
Flutter Course
An interactive Flutter course where you code, test, and build apps directly in your browser.
S.O.L.I.D. Course
Learn the principles of how software should be structured, so you can guide AI to build better systems.
D.R.Y. Course
Learn to identify and eliminate code duplication, making your codebase cleaner and easier to maintain.
System Design Course
Learn how APIs, databases, caching, and load balancing fit together to build scalable systems.
Interactive courses
Every lesson is an exercise with instant feedback.
Apply your first principle now
One exercise. Real code. Instant feedback.