Apr 3
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00:00 - Why Core Entities & API Contracts Matter 00:30 - Defining Core Entities for Architecture 01:25 - API Contracts That Shape the Client 02:45 - Error Contracts on Mobile 03:15 - Newsfeed API Contract Walkthrough In this video, we break down the step that most candidates skip in mobile system design interviews — defining core entities and API contracts before jumping into architecture. This is part of a larger framework for answering mobile system design interviews. Without entities and contracts, your design stays fuzzy. With them, caching, pagination, state management, and screen behavior all become concrete. Dylan, a Senior iOS Engineer with 8 years of experience across startups and large-scale companies, walks through how to define domain objects, major API contracts, and error handling using a newsfeed app as a concrete example. Resources: Full framework video: https://www.youtube.com/watch?v=AvvkXubYnWU Free written guide with diagrams and examples: skool.com/free-mobile-system-design