A-Book

A-book is the broker model where every client trade is routed directly to external liquidity providers. The broker doesn't take the other side of trades — they just pass orders through to the interbank market and collect a commission or small spread markup. Because the broker doesn't profit from losses, there's no conflict of interest. A-book is how ECN and STP brokers operate by default. Every trade goes through to LPs regardless of whether the client is winning or losing. The broker's profit comes from execution fees, not from client losses. Many hybrid brokers run A-book and B-book simultaneously. Profitable or high-volume clients are automatically routed A-book (so the broker doesn't eat their wins). Losing or small clients are kept B-book (so the broker profits from their losses). The client usually doesn't know which book they're on.