Design patterns,
finally simple.
The only resource that takes you from "what is a Singleton?" to acing the system design round — with diagrams, live code, flashcards, and a timed interview simulator built in.
37
Design Patterns
8
Code Languages
30+
FAANG Questions
100%
Free
Everything you need to master patterns
Not just definitions — interactive tools that build real, lasting understanding.
Interview Simulator
45-minute timed sessions with real FAANG-style questions. One at a time, no peeking. Full debrief with model answers at the end.
Start a session →Flashcard Mode
Flip-card drills for every pattern. Filter by category or difficulty, mark what you know, keep drilling the rest — spaced-repetition style.
Drill patterns →Code Playground
Write and run pattern implementations in Python, Java, TypeScript, Go, Rust, C++, C#, or JavaScript — live, in the browser, no setup.
Open playground →Pattern Recognition
See a code snippet — name the pattern. The inverse of studying definitions. This is how patterns actually appear in interviews.
Test yourself →Anti-Patterns & War Stories
Every pattern page includes how it goes wrong in production — with real symptoms, a concrete war story, and the fix. Written from a principal engineer perspective.
See an example →Progress Dashboard
Track learned patterns by category, maintain a daily streak, see what to study next, and pick up right where you left off — all saved locally.
View dashboard →Built for every level
Whether you're learning your first pattern or hardening production systems, there's something here for you.
Junior
- →ELI5 explanations for every pattern
- →Guided decision tree to find the right pattern
- →Fill-in-the-blank and multiple-choice practice
- →Roadmap: learn patterns in the right order
Mid-level
- →Interview mode on every pattern
- →FAANG-style interview simulator
- →Pattern comparison side-by-side
- →System design real-world mapping
Senior / Principal
- →Production notes: thread safety, scale, gotchas
- →Anti-pattern war stories from real systems
- →Compound pattern architectures (CQRS, Circuit Breaker…)
- →Code playground to prototype ideas in 8 languages
Popular Patterns
View all 37 →Singleton
Ensure a class has only one instance, and provide a global point of access to it.
Observer
Define a one-to-many dependency where when one object changes state, all its dependents are notified automatically
Decorator Pattern
Add responsibilities to objects dynamically
Strategy
Define a family of algorithms, encapsulate each one, and make them interchangeable
RAG
Ground LLM responses in real data by retrieving relevant documents before generating an answer.
Feature Store
Centralize feature computation, storage, and serving so training and inference always use the exact same data.
Power user tip
Press ? anywhere to see keyboard shortcuts · j/k to navigate sections · g p to jump to patterns
One design pattern a day.
Get a short, practical breakdown of one pattern every morning — the core idea, a real-world use case, and a mini coding challenge. Takes 3 minutes. Builds real fluency.
Today's pattern preview
Factory
Centralize object creation so clients never know concrete types — plug in any DB driver without touching business logic.
Ready to actually learn design patterns?
Start with one pattern. Use the flashcards to drill it. Run the simulator the day before your interview.