Replace by Fee

Replace by Fee (RBF) is a Bitcoin protocol tool created by well-known blockchain developer Peter Todd that allows one version of an unconfirmed transaction to be replaced by another that pays a higher transaction fee. Unconfirmed transactions are stored in the mempool via RBF, which is where valid transactions await confirmation by the Bitcoin network. These saved transactions can then be replaced with another transaction if the sender of the original transaction offers to pay a higher transaction fee. As a result, while RBF can help reduce network congestion and prioritize transactions based on senders’ willingness to pay, the mechanism is somewhat controversial because it alters the immutability of the transactions involved.