Code Room
Practice the whole technical round. Coding, system design, code review, and on-call — drilled by level, role, and subject, run against tests in the browser, and graded by a coach, not a judge.
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Coding Write, debug, and run code against tests — narrated. System design Design an architecture, clarify, scale, trade off. Code review Read a diff — find the bug, the smell, the risk. On-call Diagnose an incident, mitigate, write the postmortem. Vibe coding Direct an AI to build it — then catch what it got wrong.
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Interview domain
Distributed systems Databases & SQL ML systems Networking & APIs Storage & CDN Security Algorithms & data structures Reliability & on-call Concurrency Code quality & review
Subject
Data modeling Scalability Realtime Queues streaming Consistency Storage cdn Ml system design Caching Messaging queues Real time systems
Show more System design Medium
Design a URL shortener that serves billions of redirects per day with sub-10ms latency. Walk through key generation, the read and write paths, and how you keep redirects fast as…
sd-p001 Scalability · Mid–Senior · ~45 min · Distributed systems
System design Hard
Design a distributed rate limiter for an API gateway handling ~1M requests/sec across 50 edge locations, enforcing per-tenant per-endpoint quotas. How do you keep limits accurate…
sd-p002 Api design · Senior–Staff · ~45 min · Networking & APIs
System design Hard
Design a social media home feed (timeline) for 500M users. Compare fan-out-on-write versus fan-out-on-read and explain how you handle celebrity accounts with tens of millions of…
sd-p003 Scalability · Senior–Staff · ~45 min · Distributed systems
System design Hard
Design a real-time messaging system supporting 1:1 and group chats with delivery receipts, read receipts, and presence, for hundreds of millions of users.
sd-p004 Realtime · Senior–Staff · ~45 min · Distributed systems
System design Medium
Design a push notification service that delivers to iOS, Android, email, and SMS, handles provider rate limits and retries, and never sends the same notification twice.
sd-p005 Queues streaming · Mid–Senior · ~45 min · Distributed systems
System design Hard
Design the driver-rider matching/dispatch system for a ride-hailing app in a dense city, including how you find nearby drivers and handle surge demand.
sd-p006 Scalability · Senior–Staff · ~45 min · Distributed systems
System design Hard
Design a payment ledger that records money movements with double-entry accounting, exactly-once semantics, and end-of-day reconciliation. Correctness matters more than latency.
sd-p007 Consistency · Senior–Staff · ~45 min · Databases & SQL
System design Medium
Design a distributed in-memory cache (like Memcached/Redis at scale) used as a read-through layer in front of a database. Address sharding, evictions, and hot keys.
sd-p008 Caching · Mid–Senior · ~45 min · Distributed systems
System design Medium
Design a search autocomplete / typeahead service that returns the top suggestions within ~50ms as the user types, ranked by popularity.
sd-p009 Search indexing · Mid–Senior · ~45 min · Databases & SQL
System design Hard
Design a file storage and sync service (like Dropbox) that syncs files across a user's devices efficiently, including large files and conflicting edits.
sd-p010 Storage cdn · Senior–Staff · ~45 min · Storage & CDN
System design Medium
Design a video-on-demand streaming platform: how do uploaded videos get processed and delivered to millions of viewers at varying network speeds?
sd-p011 Storage cdn · Mid–Senior · ~45 min · Storage & CDN
System design Hard
Design a real-time ad-click (or event) aggregation system that produces accurate per-campaign counts over time windows, tolerant to duplicate and late-arriving events.
sd-p012 Queues streaming · Senior–Staff · ~45 min · Distributed systems
System design Medium
Design a global gaming leaderboard that supports top-N queries and 'rank around me' for tens of millions of players, updated in near real-time.
sd-p013 Caching · Mid–Senior · ~45 min · Distributed systems
System design Medium
Design a 'find nearby' service (drivers, restaurants, or friends) that answers proximity queries over millions of moving and static points.
sd-p014 Scalability · Mid–Senior · ~45 min · Distributed systems
System design Hard
Design a distributed web crawler that fetches billions of pages, respects politeness/robots rules, and avoids re-crawling the same content.
sd-p015 Scalability · Senior–Staff · ~45 min · Distributed systems
System design Hard
Design a metrics, monitoring, and alerting system that ingests millions of time-series data points per second and supports dashboards and threshold alerts.
sd-p016 Observability · Senior–Staff · ~45 min · Reliability & on-call
System design Hard
Design a distributed job/cron scheduler that runs millions of scheduled tasks reliably, with at-least-once execution and no single point of failure.
sd-p017 Queues streaming · Senior–Staff · ~45 min · Distributed systems
System design Medium
Design a feature-flag and dynamic-configuration service that serves flag evaluations to thousands of app servers with single-digit-millisecond reads and supports gradual rollouts…
sd-p019 Consistency · Mid–Senior · ~45 min · Databases & SQL
System design Hard
Design a multi-region key-value store. Discuss the replication strategy and the consistency model, and how you resolve conflicting writes across regions.
sd-p020 Consistency · Staff · ~45 min · Databases & SQL
System design Hard
Design an order-management system for e-commerce using event sourcing and CQRS. How do you keep the order lifecycle consistent across inventory, payment, and shipping?
sd-p021 Data modeling · Senior–Staff · ~45 min · Databases & SQL
System design Medium
Design an image CDN that serves user-uploaded images with on-the-fly resizing and format conversion (e.g., WebP/AVIF) while maximizing cache hit ratio.
sd-p022 Storage cdn · Mid–Senior · ~45 min · Storage & CDN
System design Hard
Design a real-time collaborative document editor (like Google Docs) where many users edit the same document simultaneously without losing changes.
sd-p023 Realtime · Staff · ~45 min · Distributed systems
System design Hard
Design the serving system for a product recommendation model: it must return personalized recommendations within ~100ms and stay fresh as user behavior changes.
sd-p024 Ml system design · Senior–Staff · ~45 min · ML systems
System design Hard
Design a real-time fraud-detection system for payment transactions that scores each transaction in-line within the authorization window and improves from labeled outcomes.
sd-p025 Ml system design · Senior–Staff · ~45 min · ML systems
System design Hard
Design a distributed coordination service that other services use for leader election, distributed locks, and configuration — the primitive ZooKeeper or etcd provide. What…
sd-p026 Consistency · Senior–Staff · ~45 min · Databases & SQL
System design Hard
Design the backend for a real-time multiplayer game (e.g., a battle arena) where many players share a fast-changing world state with low latency and cheat resistance.
sd-p027 Realtime · Senior · ~45 min · Distributed systems
System design Hard
Design a centralized logging pipeline that ingests terabytes of logs per day from thousands of services and lets engineers search them in near real-time.
sd-p028 Observability · Senior–Staff · ~45 min · Reliability & on-call
System design Hard
Design the inventory system for an e-commerce site that must prevent overselling during a flash sale where thousands try to buy the last few units simultaneously.
sd-p029 Consistency · Senior–Staff · ~45 min · Databases & SQL
System design Medium
Design a content delivery network (CDN) layer for a high-traffic site: serve assets close to users, keep caches fresh, and handle invalidation.
sd-p030 Storage cdn · Senior · ~45 min · Storage & CDN
System design Medium
Design a transactional email sending service used by many internal teams: queue and send millions of emails reliably, respect provider limits, and handle bounces and complaints.
sd-p031 Queues streaming · Mid–Senior · ~45 min · Distributed systems
System design Medium
Design a service that generates globally unique, roughly time-ordered 64-bit IDs at high throughput across many machines, without coordinating on every call.
sd-p032 Scalability · Mid–Senior · ~45 min · Distributed systems
System design Medium
Design a comment system for a high-traffic site supporting nested replies (threads), pagination, and fast reads.
sd-p033 Data modeling · Mid–Senior · ~45 min · Databases & SQL
System design Hard
Design a 'trending now' system that surfaces the top-K most popular items (hashtags, searches) over a sliding time window, updated continuously.
sd-p034 Queues streaming · Senior–Staff · ~45 min · Distributed systems
System design Hard
Design a distributed task queue that lets services enqueue background jobs and a pool of workers process them reliably, with retries and priorities.
sd-p035 Queues streaming · Senior · ~45 min · Distributed systems
System design Hard
Design a hotel (or flight) booking system that lets users search availability and book rooms without ever double-booking the same room.
sd-p036 Consistency · Senior · ~45 min · Databases & SQL
System design Medium
Design a calendar and scheduling service supporting events, recurring events, invitations, and free/busy availability lookups across many users.
sd-p037 Data modeling · Mid–Senior · ~45 min · Databases & SQL
System design Hard
Design the order-matching engine of a stock exchange: it matches buy and sell orders with low latency and strict fairness, maintaining a consistent order book.
sd-p038 Realtime · Senior–Staff · ~45 min · Distributed systems
System design Hard
Design a content-moderation pipeline for user-generated posts that combines automated classification with human review and acts within seconds for the worst content.
sd-p039 Ml system design · Senior · ~45 min · ML systems
System design Hard
Design an experimentation (A/B testing) platform that assigns users to variants, guarantees consistent assignment, and measures outcomes.
sd-p040 Data modeling · Senior · ~45 min · Databases & SQL
System design Hard
Design a distributed tracing system that follows a request across dozens of microservices and shows end-to-end latency breakdowns.
sd-p041 Observability · Senior · ~45 min · Reliability & on-call
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