This repository is an educational reference and study guide for system design interviews. It is not a deployable application or data pipeline. It provides a structured index of system design topics, solution sketches for common design problems (e.g., pastebin, Twitter, web crawler), and Python code snippets illustrating key patterns like LRU caching, hash tables, BFS on social graphs, and MapReduce. The material is oriented toward preparing engineers for technical interviews, with back-of-the-envelope calculations, REST API designs, and scalability discussions. The code examples are minimal, self-contained, and demonstrate fundamental computer science patterns, but are not production-grade software. The repository also includes Anki flashcard decks for spaced repetition.