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One platform for system design, machine coding, and DSA interviews

Ace Every Interview Round -
HLD, LLD & DSA

In-depth prep across all three: high-level design (HLD) with real architectures and trade-offs, low-level design (LLD) with patterns and runnable code, and 390 DSA problems with an in-browser judge. Plus 60 topics on AI engineering and agents, for the round that is now showing up in general loops.

Start Your Prep Roadmap →
HLD · LLD · DSA · New content added weekly
New Design Twitter (X) - Social Media Feed Fan-Out · Timeline Caching · Kafka · Redis · Celebrity Problem
39System Designs
22LLD Problems
390DSA Problems
53Core Concepts
60AI Topics
9Company Guides
Why engineers prefer SystemCraft
Not just another "Design X" list. Here's what's different.

All Three Rounds, One Place

HLD system design, LLD machine coding, and DSA - prepped end to end. Stop stitching together five different sites.

Runnable Code + Live Judge

LLD patterns and 390 DSA problems come with working solutions in Java, Python, C++, and JavaScript - run and test them in the browser.

Bad → Good → Great Depth

Every design deep dive and DSA editorial shows WHY the naive approach fails before the fix. You learn trade-offs, not just answers.

New to system design? Start with the fundamentals. 53 core concepts - caching, sharding, consistency, queues, transactions, load balancing - explained with diagrams, plus 180+ terminology distinctions interviewers ask.
Explore 53 Concepts →
Choose your interview round
Each path is tailored to a specific round type. Pick yours and start.

System Design (HLD)

Distributed architectures with diagrams, technology choices, and deep dives. Covers everything from URL Shortener to Payment Systems.

39 designsBeginner → Advanced

Machine Coding (LLD)

OOP problems with design patterns, runnable code, and company tags. Built for real machine coding rounds.

StrategyStateObserver

DSA / Coding Round

390 pattern-based problems with an in-browser judge and solutions in Java, Python, C++, and JavaScript. Curated lists for 1-week, 4-week, and 8-week preps.

390 problemsOnline JudgeQuick-Fire 50
Read it. Build it. Draw it.
Most sites stop at the article. Reading a design doesn't mean you can produce it on a whiteboard with someone watching - so here you close the loop on the same architecture.
1

Read the design

39 architectures with trade-offs, back-of-envelope numbers, and deep dives on the parts interviewers actually push on.

Browse designs →
2

Build & break it Simulator

31 of the 39 designs are playable. Drag real components onto a canvas, push the design's target load through it, and watch which tier saturates. Scored against an interview rubric.

Open the simulator →
3

Draw it from memory Whiteboard

A blank canvas with system-design shape libraries loaded. If you can reproduce the architecture without looking, you know it.

Open the whiteboard →
New: Salary bands + personal application tracker Estimated total-comp for 255 India companies by level (SDE-1/2/3). Filter by location and category, sort by pay, and - once you sign in - track every application with a Status and Comments that sync across devices.
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Most Popular
Where most readers start.

Become an AI Engineer

36 deep dives from zero to production: RAG, embeddings, evals, agents, prompt injection, LLM serving, cost and latency.

AIFull Track

Design Uber / Lyft (Ride Sharing)

Real-time matching, Redis Geo sharding, surge pricing with H3 hexagons, WebSocket tracking.

HLDAdvanced

Digital Wallet (PhonePe / Venmo)

Double-entry ledger, saga pattern, idempotency, distributed transactions. Fintech favorite.

HLDAdvanced

Parking Lot (LLD)

Classic machine-coding round: OOP class design, strategies for pricing and allocation, runnable code.

LLDMachine Coding

Splitwise (LLD)

Expense sharing with balances and settlements - entities, services, and design patterns in clean code.

LLDMachine Coding

LRU Cache

Hash map + doubly linked list in O(1). One of the most-asked coding problems - solve it in the in-browser judge.

DSAMedium

DSA Problemset + Online Judge

390 pattern-based problems with instant verdicts in Java, Python, C++, and JavaScript. Curated 50 / 75 / 150 lists.

DSAStart Here
Company-Specific Prep
Curated problems by company. Know what they ask before you walk in.

Amazon

URL Shortener, Chat System, Rate Limiter, Notification System, Parking Lot.

HLD + LLD + DSA

Google

Key-Value Store, Google Docs, YouTube, Rate Limiter. Hard DSA.

HLD + DSA

Flipkart

Twitter Feed, URL Shortener, Parking Lot, Splitwise. Machine coding heavy.

HLD + LLD + DSA

Uber

Ride Sharing, Food Delivery, Job Scheduler. Real-time and geo-heavy.

HLD + DSA

View all 9 companies → · Salary bands by level (SDE-1/2/3) →

Not sure where to start?

The interview guide tells you exactly what to study based on your timeline and level.

See the Full Roadmap →