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API Design System Design Case Studies

InterviewSkool tracks 41 API Design case studies with architecture diagrams, scale estimates, and deep dives.

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Topics

Distributed Systems 90Real-time 51Storage 43Data Pipelines 42API Design 41Databases 38Caching 37Security 32AI / ML 23Algorithms 20Scheduling 20Search 19Event Driven 14Fintech 14Payments 11Geospatial 11Analytics 11Observability 11E-commerce 11Messaging 10CDN 9Concurrency 8Ads 8Frontend 8Booking System 6Networking 5IoT 4Media 3Media Streaming 3Collaboration 3Rate Limiting 2
API DesignClear all
Access Control System (RBAC + Resource Permissions)
6 min readSecurityDatabasesAPI Design
Intermediate▶ Mock
Android MVVM Architecture for API-Driven Screens
4 min readFrontendAPI DesignCaching
Intermediate▶ Mock
Calendar Service (Google Calendar)
6 min readSchedulingDistributed SystemsStorage
Intermediate+2▶ Mock
Cloud Console Home Page (Backend-for-Frontend)
4 min readFrontendAPI DesignCaching
Intermediate▶ Mock
Coffee Ordering System with Real-Time Notifications
6 min readE-commerceReal-timeAPI Design
Beginner▶ Mock
Color Suggestion System (Adobe)
4 min readAI / MLAPI DesignCaching
Intermediate▶ Mock
Credit Card Customer Portal
5 min readFintechSecurityAPI Design
Beginner▶ Mock
CRUD APIs with Asynchronous Background Jobs
4 min readAPI DesignSchedulingDatabases
Beginner▶ Mock
Daily Puzzle Platform (Wordle-style)
3 min readAPI DesignCachingDatabases
Beginner▶ Mock
Distributed Rate Limiter
8 min readRate LimitingDistributed SystemsAPI Design
Intermediate+9▶ Mock
Reusable Dropdown / Select Component (Frontend System Design)
4 min readFrontendAPI Design
Intermediate▶ Mock
Demand-Side Ad Platform: Campaigns, Targeting and Edit History
3 min readAdsDatabasesAPI Design
Intermediate▶ Mock
Fitness Tracking App (Strava-style)
3 min readGeospatialStorageAPI Design
Intermediate▶ Mock
Governed Data Service for Downstream Consumers
3 min readAPI DesignData PipelinesSecurity
Intermediate▶ Mock
Simple Greeting-Card Web App (MVP Architecture)
4 min readAPI DesignStorageCDN
Beginner▶ Mock
Storing a Hierarchy and Returning All Descendants
4 min readDatabasesAPI DesignAlgorithms
Intermediate▶ Mock
Low-Latency Holiday Lookup Service
4 min readCachingAPI DesignFintech
Beginner▶ Mock
Streaming Homepage Rows with Viewport Loading and Deduplication (Netflix)
4 min readFrontendAPI DesignCaching
Intermediate▶ Mock
Fast Host Listings Metrics Page (Airbnb)
4 min readAnalyticsDatabasesCaching
Intermediate▶ Mock
Preventing Duplicate Request Processing (Idempotency Keys)
4 min readAPI DesignDistributed SystemsPayments
Beginner▶ Mock
Interactive SQL Query Notebook (Snowflake)
4 min readAPI DesignSchedulingStorage
Intermediate▶ Mock
REST APIs for JSON Document Storage
3 min readAPI DesignStorageDatabases
Beginner▶ Mock
Large File Upload and Processing Pipeline
7 min readStorageData PipelinesSecurity
Intermediate▶ Mock
Highly Available Software Load Balancer
7 min readDistributed SystemsNetworkingAPI Design
Intermediate▶ Mock
Multi-Carrier Parcel Shipping System
4 min readE-commerceAPI DesignEvent Driven
Intermediate▶ Mock
Personal Finance Dashboard from Multiple Providers
3 min readFintechAPI DesignCaching
Intermediate▶ Mock
Multi-Vendor Integration Platform (Connectors for Email, Slack, CRMs)
4 min readAPI DesignSecurityEvent Driven
Intermediate▶ Mock
Object Storage Service (Amazon S3) with Deduplication
6 min readStorageDistributed SystemsAPI Design
Advanced▶ Mock
Offline Multi-Device E-Book Reader (Kindle-style)
3 min readStorageAPI DesignCollaboration
Intermediate▶ Mock
Online Bookstore with Price Aggregation
7 min readE-commerceAPI DesignCaching
Intermediate▶ Mock
Making Many HTTP Requests Fast (Within Rate Limits)
3 min readConcurrencyAPI DesignRate Limiting
Intermediate▶ Mock
Pastebin (Share Text by Link)
4 min readStorageCachingAPI Design
Beginner▶ Mock
Prompt Sharing Platform
5 min readAI / MLSecurityDatabases
Intermediate▶ Mock
Runtime Localization System (i18n)
4 min readFrontendAPI DesignCDN
Intermediate▶ Mock
Secure Multi-Tenant API for an Enterprise AI Copilot
4 min readAI / MLSecurityAPI Design
Advanced▶ Mock
Secure Internal Web App for Sensitive Financial Data
4 min readSecurityAPI DesignDatabases
Intermediate▶ Mock
Aggregator Service over Many Downstream Microservices
3 min readDistributed SystemsAPI DesignCaching
Intermediate▶ Mock
Tagging System with Clean REST APIs (Confluence / Jira Labels)
3 min readAPI DesignDatabasesSearch
Beginner▶ Mock
To-Do List Service (REST API and Real-Time Shared Lists)
5 min readAPI DesignReal-timeCollaboration
Beginner▶ Mock
URL Shortener (TinyURL / bit.ly)
7 min readDistributed SystemsCachingStorage
Beginner+4▶ Mock
Voting System APIs and Data Model
3 min readAPI DesignDatabasesSecurity
Beginner▶ Mock

Frequently Asked Questions

What is API Design in system design?

API Design is a core system design topic covered in 41 case studies on InterviewSkool. It appears frequently in FAANG interviews, especially at Google, Amazon, and Meta.

How should I prepare API Design for system design interviews?

Study the case studies above, focusing on architecture trade-offs, scale estimates, and API designs. Practice explaining your decisions aloud — this is exactly what interviewers evaluate.

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