About this site
System Craft is a focused guide to system design interviews — the frameworks, building blocks, and real interview problems you need to go from “I've read about it” to “I can actually whiteboard it.”
What this site is
System Craft is a curated, opinionated resource dedicated entirely to system design. It's not a grab-bag of every interview topic — it's a deep, structured walk through the one round that most decides your level and offer: the system design interview.
Everything here is written the way I'd actually explain it on a whiteboard: start from requirements, build a clean high-level design, then go deep where it matters and reason about trade-offs out loud. The goal isn't to memorize answers — it's to build a repeatable way of thinking that holds up under real interview pressure.
What you'll find
- Quick Start — How to use this guide, what interviewers actually test, a 50-minute framework, and study plans to get going fast.
- Core Building Blocks — The components you'll reach for again and again: databases, caches, CDNs, message queues, blob storage, API gateways, and search.
- Deep Dive Toolkit — The concepts that separate breadth from depth: sharding, consistent hashing, locking, idempotency, rate limiting, backpressure, and more.
- Patterns — Reusable shapes like read-heavy vs write-heavy systems, fan-out, real-time messaging, and large-file processing.
- Before the Interview / Cheat Sheets — Quick references for the final stretch: phrases, back-of-the-envelope numbers, and Strong-Hire signals.
- Problems — 25+ real interview questions worked end-to-end, from URL Shortener to Uber, Payments, YouTube, and beyond — each following the same clear, repeatable structure.
Who's behind it
This site is created by Harold, a Bay Area Senior Software Engineer and career mentor focused on helping software engineers prepare for system design interviews.
The materials here are based on real interview preparation, mock interviews, mentorship experience, and practical engineering discussions.
System design is not about naming as many technologies as possible. It is about making reasonable design decisions under constraints and explaining your thinking clearly.
That is what this site is built to help you practice.
Where to go next
Want more than the written guide? Explore the rest of my work on my System Design Course page - SystemCraft Academy:
Harold's System Design 训练营课程: learn.systemcraft.app
In System Craft Academy, you'll find my 5-week System Design Bootcamp (20+ problems worked live on a whiteboard) - a more interactive and in-person interview prep experience that helps 10+ people get their desired offer!