The System Design Primer: System Design Interview Prep
/system-design-primer
The System Design Primer is a free GitHub reference for large-scale system design and interview prep, walking through worked case studies like Pastebin, Twitter's timeline, and a web crawler. Reach for it if you want a structured path from CAP theorem to a full mock answer with diagrams; skip it if you already know the fundamentals and just need fresh practice problems to drill.
What is The System Design Primer?
The System Design Primer is a GitHub repository by donnemartin that organizes system design theory, interview questions, and sample solutions into one study path. It pairs topic write-ups on scalability, caching, and the CAP theorem with worked examples like designing Pastebin and a web crawler, plus Anki flashcard decks for spaced repetition.
Key Features for System Design Learning
- ✓Topic write-ups on core trade-offs: performance vs scalability, latency vs throughput, and availability vs consistency (CAP theorem, CP vs AP).
- ✓A four-step framework for approaching any system design interview question, from scoping constraints to scaling the design.
- ✓Worked system design case studies with sample discussions, code, and diagrams, including Pastebin, a Twitter-style timeline, and a web crawler.
- ✓A separate, explicitly 'under development' set of object-oriented design exercises covering things like an LRU cache, a parking lot, and a chat server.
- ✓Anki flashcard decks (a system design deck, a system design exercises deck, and an object-oriented design deck) for spaced-repetition review on the go.
- ✓A study guide that adjusts what to prioritize based on a short, medium, or long interview timeline.
- ✓Consistency and availability patterns spelled out with concrete failure scenarios, like active-passive vs active-active fail-over.
- ✓A companion repo, Interactive Coding Challenges, with its own Anki deck for coding-interview prep.
Who Benefits from This System Design Guide?
- •Engineers with an upcoming system design interview who need a single ordered study path instead of scattered blog posts.
- •Backend or infrastructure engineers who know how to write code but haven't had to reason about trade-offs like CAP theorem out loud before.
- •Self-taught developers building a mental model of distributed systems concepts before touching a real large-scale system.
- •Interview candidates who learn well from spaced repetition and want the Anki decks alongside the reading.
Strengths
- ✓Each system design question comes with an actual worked solution — discussion, code, and diagrams — not just a prompt.
- ✓The four-step interview framework (scope, high-level design, core components, scale) is reusable on any question, not just the ones in the repo.
- ✓Anki decks turn passive reading into spaced-repetition review, which is unusual for a GitHub study guide.
- ✓The study guide's short/medium/long timeline table helps you triage what to read instead of trying to absorb everything.
Scope and Limitations of the Primer
- △The object-oriented design interview section is explicitly marked 'under development' in the README, with several exercises still unsolved and open for contribution.
- △It's a static reading list, not an interactive platform — there's no built-in way to practice out loud or get feedback on your own design.
- △License field isn't specified in the metadata pulled for this review, so check the repo directly before reusing large chunks of the content.
- △Some of the linked external articles (scalability write-ups, source links) point to older third-party posts and archive.org captures rather than fresh material.
Other Resources for System Design Prep
Frequently Asked Questions
The System Design Primer works best for engineers with some coding background who are new to thinking about scale — total beginners may need to slow down on topics like the CAP theorem, while senior architects will likely skim familiar sections.
The System Design Primer includes sample solutions with discussion, code, and diagrams for its system design and object-oriented design questions, though the object-oriented section is still being filled in.
The System Design Primer accepts pull requests for fixing errors, adding sections, and adding translations, per the contributing guidelines linked in the repo.
The System Design Primer ships three Anki flashcard decks — a system design deck, a system design exercises deck, and an object-oriented design deck — built for spaced-repetition review on the go.
The System Design Primer covers scalability, performance vs scalability, latency vs throughput, availability vs consistency (CAP theorem), consistency patterns, and availability patterns like fail-over, alongside worked interview case studies.
The System Design Primer is built around interview prep, but the same topic write-ups on caching, replication, and consistency trade-offs apply just as well to real architecture decisions outside of interviews.
Who should try it — and who should skip
Try The System Design Primer if you're a software engineer with a system design interview scheduled and want one ordered path through the fundamentals instead of forty open browser tabs. Skip it if you're already comfortable explaining CAP theorem and sharding trade-offs from memory — you're better served by fresh, unfamiliar practice questions than by rereading a primer you've outgrown.
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