Design
Online Stock Brokerage
Design an online stock trading system where users place buy/sell orders that are matched through an order book.
01 - Why interviewers ask this
It touches order-matching and portfolio math, both classic fintech LLD themes — interviewers use it to see if you separate order types cleanly and keep balance updates atomic.
02 - Where this system exists in the real world
You interact with this design every day.
Robinhood / Zerodha-style trading platforms
Portfolio tracking and management tools
Exchange order-matching engines (simplified)
03 - What you'll master
Solve this once. Know it forever.
Model different order types (market, limit, stop)
Keep buy/sell balance updates atomic
Compute portfolio value and P&L correctly
04 - What you'll design
7 functional · 4 non-functional requirements.
Users place market orders and limit orders to buy or sell stocks
6 more requirements inside
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05 - Companies that ask this
You may face this exact question in your next interview.
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