All or None Order (AON)

AON (All or None) orders are a type of order in which the entire order must be filled or none of it will be executed. This is often used to ensure that a trader only buys or sells an asset in a single transaction rather than in pieces. Unlike standard limit orders that can be partially filled over time as matching orders become available, an AON order will remain unfilled until counterparty liquidity exists to fill the entire quantity in one execution, and will be cancelled if the condition cannot be met within the order's valid timeframe.

All or None orders are particularly useful for strategies where partial fills create problems — for example, certain arbitrage strategies require buying and selling specific quantities simultaneously, and a partial fill on one leg could leave a trader with unintended exposure. AON orders provide certainty of execution size at the cost of potentially lower fill rates, since the order will be skipped by the matching engine if full liquidity is not available at the specified price.

Trading bots can use AON orders as a risk management tool within complex multi-asset strategies where position sizing must remain precise. However, traders should be aware that not all exchanges support AON order types natively, and availability varies by market and asset class. When AON orders are not available, some traders simulate the behavior programmatically by monitoring partial fills and cancelling the remainder if the full quantity is not filled within an acceptable timeframe, though this approach carries its own execution risks.