Private mempool (private RPC)

Normally a signed transaction is gossiped to the public mempool, where anyone, including MEV bots, can see it before it lands in a block. A private mempool, usually reached through a private RPC endpoint, skips that step: the wallet hands the transaction to a service that forwards it only to selected builders, so it stays invisible until it is included.

The main use is protection from sandwich attacks and front-running on decentralised exchanges. Services such as Flashbots Protect and MEV Blocker offer this for free, some wallets route swaps privately by default, and order flow auctions go further by letting searchers bid to back-run a trade and returning part of the profit to the user. Large traders, DAOs and liquidators also use private routes to avoid tipping off competitors.

Privacy here means trusting the RPC operator and the builders not to exploit the order flow themselves. If few builders receive the transaction, inclusion can be slower. Private routing also hides some transactions from public monitoring, and attackers have used it to conceal exploits.