YOUR BRIEF
What to work through
Work through online chess as a spoken system design interview. Start by clarifying the scope, sketch a working design and explain the trade-offs behind your choices.
- Find an opponent of similar skill and start a game
- Play moves in real time, with the server checking every move and running both clocks
- Ratings go up on a win and down on a loss
- View the global leaderboard and your own rank, updated shortly after each game
BEFORE YOU START
Constraints to discuss
- 10 million registered players
- 500,000 concurrent games at peak, so 1 million open connections
- Clocks stay fair when the two players have different network delays
- A player is never in two games at once
Need a starting point?
Watch for these common gaps as you prepare:
- Trusting the client for moves, clocks or timestamps
- Checking that a player is free and pairing them in two separate steps
- Keeping games only in memory with no move log
- Computing a player’s rank with a count over 10 million rows on every request
Why this question is in the collection
These sources connect the problem to company interview reports or preparation guides. They do not guarantee what a company will ask you.