What Is a Private Mempool?
A private mempool is a side door. Instead of broadcasting your swap into the public mempool, where MEV bots can sandwich it, you send it down a private pipe to a block builder who promises not to leak it. Wallets market this as "MEV protection." It is real, useful, and not magic.
How It Actually Works
- Services like Flashbots Protect, and various wallet RPC toggles, accept the transaction privately and include it in a block bundle. If it cannot be included cleanly, it can fail without becoming public bait.
- Someone still orders the block. Private often means "not public to every searcher," not "invisible to the builder." Builders and relays see flow. Some run orderflow auctions: your intent is bid on, and you may get a refund of some extracted value. That is a better deal than a sandwich. It is still extraction with a kickback.
- This is the same family of choice as picking an RPC. The pipe is a trust assumption. Official endpoints only.
Risks and Common Mistakes
- Leaving slippage wide because "protection is on." Tight slippage is still the retail seatbelt. Protection reduces who can see you; it does not make a thin pool deep.
- Random "private RPC" links from Twitter. A malicious endpoint can drop, delay, or rewrite what you think you sent.
- Believing private flow equals anonymity. Your address, size, and destination still land on-chain in the block. Explorers still show the trade.
When It Matters
Any DEX trade large enough to be lunch, especially on Ethereum mainnet. Pair it with the simulation habit in my Rabby review and the routing habit in my Jupiter review.
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