정의
Best bid / ask
The highest standing buy price and the lowest standing sell price on the order book.
Best bid / ask
The best bid is the highest standing buy price on an order book, and the best ask is the lowest standing sell price. Together they form the top of the CLOB: the single best prices at which someone is currently willing to buy or sell an outcome.
In context
On Polymarket the CLOB (Central Limit Order Book) publishes these values in real time. The Market WebSocket emits a best_bid_ask event whenever either side changes. Traders use the best bid and best ask to gauge immediate executable prices, estimate midpoint and spread, and size orders to avoid immediate fills or to capture liquidity.
A few practical notes:
- For binary markets the theoretical fair prices of YES and NO are complementary and their best bids/asks sit on opposite sides of the book.
- Tick size changes (e.g. tightening from $0.01 to $0.001 near extremes) can alter how close best bid and best ask can be.
- Maker fees on Polymarket are zero; taker fees vary by category. Fee changes and order execution fees affect realized costs when crossing the spread.
See also
- /glossary/midpoint
- /glossary/spread