RizonMake me a market: a free market-making game, with no sign-up
Quote a bid and an ask, trade with informed traders and flow, and see your PnL. The market-making interview game, free to play with no sign-up.
Short answer: "Make me a market" means: give a bid and an ask on a number you can't know for sure, then trade with whoever thinks your price is wrong. It's a classic trading-interview exercise. Play a hand below. It takes about a minute.
How the game works
- The number is the sum of five cards: yours, Trader A's, Trader B's and two in the middle. An ace is 1 and a king is 13.
- You quote three times. Each round you set a bid and an ask, up to 6 wide. A middle card turns up after each of the first two rounds.
- Traders A and B each see their own card. They buy at your ask or sell at your bid when your quote looks wrong to them.
- Flow has no view. It trades either side at random: always at 1 wide or tighter, less as your quote widens, and not at all at 5 wide.
- The end: every trade settles at the sum, and each point is worth $10.
So there are two ways to lose and one way to win. Flow pays you the spread. Traders A and B take it back when your price is wrong, and flow stays away when your quote is too wide.
How to quote well
We played 100,000 hands of each habit below, using the game's own code.
| How you quote | Average PnL a hand ($) | Hands won (%) |
|---|---|---|
| Ignore your cards: 34 bid, 36 ask, every round | −136 | 45 |
| Fair on your cards, 1 wide, never move for a trade | −67 | 47 |
| Fair on your cards, 3 wide, never move for a trade | −8 | 58 |
| Fair, moved after each trader's trade, 1 wide | −5 | 53 |
| Fair, moved after each trader's trade, 2 wide | +31 | 63 |
| Fair, moved after each trader's trade, 3 wide | +44 | 67 |
| Fair, moved after each trader's trade, 4 wide | +38 | 64 |
| Fair, moved after each trader's trade, 6 wide | +16 | 45 |
Four habits explain that table.
Start from fair. Add the cards you can see, then count each unseen card at about 7. Holding a 9 with four cards unseen, fair is about 9 + 4 × 7 = 37. (Exactly, it's 36.8, because the cards left in the deck average 6.96.)
Pick a width that pays for what you don't know. A 1-wide quote gets all the flow but earns only 0.5 a trade, and the traders pick it off. A 6-wide quote is safe, but flow never comes. About 3 wide earned the most.
Move when a trader trades. In the table, this is worth about $50 a hand. Say you quote 35.5 bid, 38.5 ask, and Trader A buys. A needs its own view to beat 38.5 by at least 0.5, which takes a queen or a king. Moving up 2 or 3 points was about right in our runs, and the next card you see tells you more.
Watch your position. Leaning your quote against your position cut the swing of a hand by about 7%, and gave up about $6 of average PnL. In three rounds that's a matter of taste. A real book has no last round, so inventory matters more there.
What interviewers look for
One guide to these interviews names Jane Street, IMC and Optiver among the firms that ask candidates to make markets on unknown quantities. It lists what gets scored:
- Arithmetic speed and accuracy under time pressure
- Choosing a width and updating it as information arrives
- Adverse selection: people trade with you when your price is wrong in their favor
- Inventory: skewing your quotes to reduce a position
- Reasoning out loud: why you chose your width, and what changed your view
The usual mistakes are freezing while chasing an exact answer, leaving a stale quote up after new information, and treating the interviewer as an opponent rather than a source of information. Interview formats vary and aren't published, so treat this as a guide's summary.
From the game to a real book
The job is the same on a live market: quote both sides, earn the spread, and don't be the stale price. Rizon's books are open with practice money and no sign-up, so you can rest real orders against real flow, or run a bot through the API.
- How do market makers make money? The arithmetic behind this game.
- How to make markets in horizon contracts. Quoting strikes on a live book.
- A quant project for your resume. Build a market maker and show its record.
- The bot record. What the takers and makers on Rizon actually earn.
FAQ
What does "make me a market" mean?
It means quote a two-sided price: the bid you'd buy at and the ask you'd sell at, on a number nobody knows for sure. The other person can then buy from you, sell to you or pass.
How wide should my market be?
Wide enough to cover what you don't know, and tight enough that someone wants to trade. In this game about 3 points wide earned the most. In an interview, you'll often be given a maximum width.
What should I do when someone trades with me?
Ask what they know. A trade with an informed person is a clue that your price is wrong on that side, so move your quote toward it. In this game, moving 2 or 3 points after a trader's trade took a hand from about −$8 to about +$44 on average.
Is this what trading firms ask in interviews?
It's the same idea, not their exact game. Real rounds vary by firm and often use estimates rather than cards, like "make me a market on the height of a building". Practicing the habits matters more than the format.
Is the game free?
Yes. There's no sign-up, no download and nothing to pay. It runs in your browser, and it keeps your running total on your device.