An order book is just a live list of what people will pay (bids) and what they'll accept (asks) for a Yes share. Once you can read it, you can spot a fair, liquid market versus a thin one where you'll get a terrible fill. Here's the whole thing in plain English.
Every prediction market share pays $1 if the outcome happens and $0 if it doesn't, so a price of 63¢ means the market will pay 63¢ to buy a Yes share. The order book stacks all the open buy orders (bids) below the current price and all the open sell orders (asks) above it. Nothing trades until a bid and an ask meet.
The best bid is the highest price someone will pay right now; the best ask is the lowest price someone will sell at. The "price" you see quoted is usually the last trade or the midpoint between them. If the best bid is 60¢ and the best ask is 66¢, the true market is somewhere in that range — not exactly at either number.
The gap between best bid and best ask is the spread. A 1–2¢ spread is tight and healthy; a 10¢ spread means you lose a lot the instant you enter (buy at the ask, and you're already down relative to the midpoint). Wide spreads are the #1 sign of a market you should size small in or skip.
Depth is how many shares are stacked at each price level. A market can show a tight spread but have only 20 shares at the best ask — buy 500 and you'll "walk the book," filling at worse and worse prices. Always check how many shares sit near the top before assuming your whole order fills at the quoted price.
A market order takes whatever the book offers right now — fast, but you pay the spread and any depth cost. A limit order sets your price and waits; you might get filled cheaper, or not at all. In thin prediction markets, patient limit orders inside the spread are usually the smarter play.
Deep market: tight spread, hundreds of shares at each level, prices that barely move when you trade. Thin market: wide spread, tiny size, and a price that lurches when anyone acts. The order book shows you which one you're in before you commit — that read alone will save you more than any prediction skill.
Not every order in the book is real intent. In thin prediction markets, someone can post a big bid or ask to make the market look deeper or nudge the perceived price, then pull it before it fills — "spoofing." Treat a lone giant order that keeps appearing and vanishing with suspicion, and watch whether size actually trades or just sits there. Real depth gets hit; decorative depth evaporates the moment price approaches it.
The order book shows price, not your net outcome. Factor in the platform's fees (trading, and sometimes a cut of winnings) and any spread you'll pay to exit before resolution. And remember every market carries resolution risk — the question can settle in a way you didn't expect if the wording is ambiguous. A "great" entry price is only great after fees and if the market resolves the way you're assuming, so read the rules, not just the book.
Before you place an order, run through the book once: