Code Review System Low-Level Design: Diff Engine, Inline Comments, and Review State Machine
6 min read Pull Request Model A pull request (PR) represents a request to merge a source branch into a target branch. Core […] Read article
System Design
System Design
Digital Wallet Service Low-Level Design: Balance Ledger, Fund Transfer, and Reconciliation
5 min read Double-Entry Ledger A digital wallet service is built on a double-entry ledger: every financial event creates exactly two entries — Read article
System Design
Escrow Service Low-Level Design: Fund Holding, Release Conditions, and Dispute Resolution
6 min read Escrow Model An escrow service acts as a neutral third party: the buyer transfers funds to a platform-controlled escrow account, Read article
System Design
Tax Calculation Service Low-Level Design: Jurisdiction Detection, Rate Lookup, and Compliance Reporting
6 min read Tax Service Components A production tax calculation service has five distinct responsibilities: nexus determination (does the business owe tax in Read article
System Design
Ride Matching Service Low-Level Design: Driver-Rider Matching, ETA Calculation, and Surge Pricing
6 min read Ride Matching Service Low-Level Design A ride matching service connects riders with nearby drivers in real time, computing ETAs, scoring Read article
System Design
Interview Scheduling System Low-Level Design: Availability Matching, Calendar Integration, and Reminder Pipeline
6 min read Interview Scheduling System Low-Level Design An interview scheduling system matches candidate time preferences against interviewer availability, handles calendar integration, prevents Read article
System Design
Knowledge Graph Low-Level Design: Entity Storage, Relationship Traversal, and Graph Query Optimization
6 min read Knowledge Graph Overview A knowledge graph stores entities (people, organizations, places, events) and the typed relationships between them, enabling structured Read article
System Design
Search Indexer Low-Level Design: Document Ingestion, Index Building, and Incremental Updates
6 min read Search Indexer Overview A search indexer transforms raw documents into a data structure that supports fast full-text queries. The pipeline Read article
System Design
Spam Detection System Low-Level Design: Velocity Checks, Graph-Based Detection, and Classifier Ensemble
6 min read Spam Detection System Overview Spam detection combines fast rule-based velocity checks, text classification, and graph-based account analysis. No single signal Read article
System Design
Abuse Detection System Low-Level Design: Multi-Signal Risk Scoring, Account Takeover Detection, and Automated Response
6 min read Abuse Detection System Overview An abuse detection system protects users and the platform from account takeover, credential stuffing, scraping, fake Read article
System Design
Search Ranking System Low-Level Design: Relevance Scoring, Learning to Rank, and Feature Engineering
6 min read Search Ranking System Overview A search ranking system determines the order in which retrieved documents are presented to users. The Read article
System Design
Personalization Engine Low-Level Design: User Embeddings, Real-Time Signals, and Serving Infrastructure
5 min read Personalization Engine Overview A personalization engine ranks content by predicted user interest rather than global popularity. The core idea: represent Read article
System Design
Session Store Low-Level Design: Session Lifecycle, Redis Storage, and Distributed Session Affinity
5 min read What a Session Store Does A session store maintains server-side state for authenticated users across stateless HTTP requests. The client Read article
System Design
Token Service Low-Level Design: JWT Issuance, Refresh Token Rotation, and Revocation
5 min read Two-Token Architecture Modern authentication uses two token types with different properties: Access token: Short-lived (15 minutes), self-contained JWT. Resource servers Read article
System Design
Access Log Service Low-Level Design: High-Throughput Write, Structured Logging, and Query Interface
5 min read What an Access Log Service Provides Every HTTP request to a web service generates a log record. At scale, this Read article