How to read a bid-ask spread
The bid is the most anyone will pay right now; the ask is the least anyone will accept. Buy at the ask and sell at the bid in the same instant and the difference is what you lose. That is the spread.
Reading it in cents is the common mistake. Two cents on a $0.65 contract is a 3% round trip. The same two cents on a $0.08 long shot is a quarter of the position, and no forecasting edge covers that.
What makes the spread widen
Spreads widen when market makers face more risk of being picked off: thin markets, imminent resolution, and moments right after news when the fair price is unclear.
A spread that stays wide in a market with real volume tells you something on its own. It usually means the participants disagree about the price and nobody wants to post firm quotes in between.
Where 0xinsider uses the bid-ask spread
Each large trade's page shows the spread in basis points, computed from Polymarket's best bid and best ask as 0xinsider recorded the trade: a book snapshot taken after the fill (up to 30 seconds old from cache), not necessarily the spread the fill paid.
