Where slippage comes from
The screen shows the best price, not the price for your whole order. A market order takes the best resting orders first and then keeps walking up the book until it is filled, so the average fill is worse than the quote.
The gap grows with order size and shrinks with depth. In a market with 50,000 shares resting at every cent, a 2,000-share order costs nothing extra. In one with 500 shares at the top and a gap above it, the same order can move the price several cents.
How to control slippage
A limit order converts price risk into fill risk: the price is capped, and the remainder may never fill. That is usually the better trade in a market that resolves in weeks, and the worse one when a position needs to be exited before an event.
Splitting a large order over time is the other lever, though in a market thin enough to need it, the earlier fills often tip the direction to anyone watching the book.
Where 0xinsider uses slippage
Each large trade's page shows the book depth on the side the trade hit and the share of that depth the fill consumed, captured when 0xinsider ingested the trade. The same $50,000 fill means one thing in a deep election market and something else in a thin niche one.
