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

Ace Every Interview Round -
HLD, LLD & DSA

Free, 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 360+ DSA problems with an in-browser judge.

Start Your Prep Roadmap →
Free · HLD · LLD · DSA · New content added weekly
New Design Twitter (X) - Social Media Feed Fan-Out · Timeline Caching · Kafka · Redis · Celebrity Problem
31System Designs
49Core Concepts
360+DSA Problems
8Company 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 360+ 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. 49 core concepts - caching, sharding, consistency, queues, transactions, load balancing - explained with diagrams, plus 180+ terminology distinctions interviewers ask.
Explore 49 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.

31 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

360+ 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.

360+ 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

31 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

All 31 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 120+ 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.
Start your Job Hunt →
Most Popular
Where most readers start.

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

360+ 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 8 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 →
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