# Make 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.

Source: https://rizon.markets/learn/make-me-a-market (updated 2026-11-05)

> **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](https://www.techinterview.org/post/3233476306/market-making-interview-trading-games/?format=md) 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](https://rizon.markets/docs).

- [How do market makers make money?](https://rizon.markets/learn/how-do-market-makers-make-money) The arithmetic behind this game.
- [How to make markets in horizon contracts](https://rizon.markets/learn/how-to-make-markets-in-horizon-contracts). Quoting strikes on a live book.
- [A quant project for your resume](https://rizon.markets/learn/quant-project-for-resume). Build a market maker and show its record.
- [The bot record](https://rizon.markets/bots). 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.