Central limit order book (CLOB)

Also called order book · limit order book

The matching engine that pairs resting limit orders by price and time — how both Polymarket and Kalshi fill trades.

Neither venue is a bookmaker and neither is an automated market maker. You trade against other participants' resting limit orders, matched by price and then by time. That single structural fact is why prices here can be read as a live consensus rather than as a number somebody set.

The two implementations differ in ways that matter the moment you try to price a trade programmatically. Polymarket serves a book per outcome token — YES and NO are separate tokens with separate books, quoted as strings, with the best price listed last in each array. Kalshi serves one book per market containing both sides, and both sides list resting bids. So on Kalshi, buying YES means crossing the NO bids: the executable YES ask ladder is one minus each NO bid price, walked from the best NO bid downward, and the quantity available at the top of that ladder is exactly the size resting at the best NO bid.

The practical consequence is that a market does not have a price, it has a ladder. How much you can actually buy before your average fill destroys the edge is a walk down that ladder, which is why depth-aware sizing exists at all.

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Definitions describe how Polymarket and Kalshi behave and how WhaleTracks models them; venue rules and fee schedules can change, so confirm anything you size a position on with the venue itself. WhaleTracks is informational analytics, not financial advice. Past performance does not guarantee future results.