A "post-only" condition is a feature in limit orders that ensures the order will only be added to the order book if it does not immediately fill against an existing order in the order book. In other words, a post-only limit order will only be placed if it can be added as a maker order and not as a taker order.
When a trader places a post-only limit order, the exchange will check if the order matches with an existing order in the order book. If the order would immediately fill against an existing order, the post-only limit order will be rejected, and it will not be added to the order book. This means the order will not execute immediately as a market order, which could incur taker fees.
The primary purpose of the post-only condition is to encourage traders to provide liquidity to the market by placing limit orders that add depth to the order book. By doing so, traders benefit from reduced trading fees, as our exchange offers lower fees for maker orders (limit orders that add liquidity) compared to taker orders (market orders that remove liquidity).
Using the post-only option can be advantageous for traders who wish to avoid paying taker fees and prefer to participate as makers in the order book. It also helps to prevent unintended immediate executions of limit orders and encourages the maintenance of a liquid and orderly market.