Like System — Low-Level Design A like system records user reactions to content and displays counts. At scale, naive approaches […]

Comments System — Low-Level Design A comments system supports threaded discussion on content: flat comments, nested replies, sorting, pagination, and

Email Queue System — Low-Level Design An email queue system buffers outgoing emails from application code, delivers them reliably through

Waitlist System — Low-Level Design A waitlist system queues users for access to a limited resource: early access to a

Booking System — Low-Level Design A booking system manages reservations for time-slotted resources: hotel rooms, restaurant tables, meeting rooms, or

Idempotency Keys — Low-Level Design Idempotency ensures that retrying an operation produces the same result as executing it once. This

Dark Mode System — Low-Level Design A dark mode system persists a user’s theme preference, propagates it across devices, and

Payment Split System — Low-Level Design A payment split system divides a single transaction among multiple parties: splitting a restaurant

Feature Flag System — Low-Level Design A feature flag system controls feature availability without code deployments. It enables gradual rollouts,

Archive System — Low-Level Design An archive system moves cold data from primary storage to cheaper, slower tiers while keeping

Webhook Retry System — Low-Level Design A webhook retry system reliably delivers HTTP callbacks to external consumer endpoints, handling transient

What is a Product Catalog System? A product catalog stores and serves product data: names, descriptions, images, prices, variants, and

What is a Storage Quota System? A storage quota system tracks and enforces per-user limits on resource consumption: disk storage

What is a Returns Portal? A returns portal allows customers to self-service returns and exchanges: select items to return, choose

What is a Follow System? A follow system lets users subscribe to updates from other users or entities: follow a