Problem Understanding
Restate the problem in your own words.
Design Stock Trading (Robinhood)
Design a Robinhood-class retail brokerage: users browse and watch live quotes for thousands of symbols, place market / limit / stop orders, see their portfolio + P&L update in real time, and receive a tax-ready transaction history. The system is a broker (not the exchange) — orders are routed to real venues (NYSE / NASDAQ / market makers) and settled T+2 via the clearing house. The hot paths are quote streaming (tens of millions of concurrent WebSocket viewers) and order placement (with peak burst at 9:30 AM ET when the market opens). Architecture is a fan-out for market data + a regulated saga for orders and settlement.
- RobinhoodThe category-defining mobile-first retail broker; commission-free; ~25 M MAU at peak.
- Charles Schwab / Fidelity / E*TRADEEstablished brokers with the same architectural shape + decades-deep tax + compliance tooling.
- WebullRobinhood-style UI with day-trader-oriented features (Level 2 quotes, paper trading).
- Interactive BrokersPro / institutional broker; more order types, multi-exchange routing built-in.
Your task: read the problem above, then write what the system is, who uses it, the rough scale, and the headline UX expectation — in your own words. Submit for AI review when you're ready.
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