# Daily Scaffold

> Daily Scaffold is a gamified, practice-first web app for learning system design and preparing for system design interviews. You learn by answering questions and working through real design drills, five minutes a day, instead of passively reading or watching lectures.

## What it is
- 40 skills across 6 tiers, from latency basics to architecting full systems
- 487 practice questions (concept MCQs, trade-off decisions, bottleneck hunts, cloze, matching, estimation)
- 12 famous design drills: rate limiter, URL shortener, news feed, chat system, distributed key-value store, web crawler, notification service, ride-share matching, Ticketmaster seat reservation, Dropbox, Yelp proximity search, YouTube
- Gamified with XP, daily streaks, crowns, and leagues (Bronze, Silver, Gold, Sapphire, Ruby, Diamond)
- A free, public Concepts library: in-depth reference articles on system design topics, readable without an account

## Who it is for
Software engineers learning system design, and candidates preparing for technical or system design interviews at top tech companies.

## Pricing
- Free: the full Concepts reference library plus a set of starter lessons, no credit card required
- Pro: unlocks all 40 skills and 12 design drills, with a 7-day free trial

## Key pages
- Landing: /
- Concepts library (in-depth system design reference articles): /concepts
- Pricing: /pricing
- Sign in: /login

## Concepts library (in-depth reference articles)
- Designing a URL Shortener — ID generation (hashing, counters, Snowflake), Base62, the 100:1 read skew, 301 vs 302, caching the redirect path: /concepts/url-shortener
- Load Balancers — L4 vs L7, balancing algorithms, health checks, sticky sessions, SSL termination, avoiding the single point of failure: /concepts/load-balancer
- Caching Strategies — cache-aside, read-through, write-through, write-around, and write-back compared by latency, consistency, and durability: /concepts/caching-strategies
- Designing Instagram — pre-signed media uploads, polyglot storage, and hybrid feed fan-out (push for normal users, pull for celebrities): /concepts/design-instagram
- Designing a Rate Limiter — token bucket and other algorithms, atomic Redis Lua scripts, sharding to 1M req/s, fail-open vs fail-closed: /concepts/rate-limiter
- The CAP Theorem — why a network partition forces a choice between consistency and availability: /concepts/cap-theorem
- Consistent Hashing — spreading keys so adding or removing a server moves only a small fraction of them: /concepts/consistent-hashing

## Philosophy
You learn system design by making decisions, question after question, until the trade-offs feel obvious. Architecture should be reasoned about by humans, not generated by a model.