Design a Real-Time Stock Price System

Problem Statement

Design a Robinhood-like stock price system. Users should be able to view real-time stock prices and historical price charts for ranges such as 1 day, 1 week, and 1 year. The chart API should return a bounded number of datapoints instead of dumping every raw tick to the client.

Reported Robinhood interview signals for this question include:

• Users need both real-time stock prices and historical chart prices.
• The chart should support multiple ranges and granularities, especially 1 day, 1 week, and 1 year.
• Returned datapoints should not be too many for a mobile chart widget.
• Follow-ups commonly ask how Robinhood gets real-time stock prices with fault tolerance, what database to use, and how to support different ranges or granularities.
• Some variants frame this as extending existing implementations to support a mobile-app-style stock price widget.

Do not turn this into a stock order management system. This is a market-data read path: ingest quotes and trades, maintain latest prices, precompute chart candles, and serve low-latency mobile/web reads with clear stale-data behavior.

Common Aliases

• Design a Robinhood-like stock price system
• Realtime Stock Price System
• Real-time stock price chart system
• Stock price chart widget design
• Design market data for a trading app