MEV Protection

MEV protection is the set of tools and techniques that stop users' blockchain transactions from being exploited by bots seeking maximal extractable value. The main threats are front-running and sandwich attacks, in which a bot sees a pending trade and places its own orders around it, giving the user a worse price. Protection usually works by hiding transactions from the public queue until they are included in a block, or by changing how trades are matched so that order within a block matters less.

Protection is offered by wallet providers, decentralised exchanges, aggregators and specialist services. One of the best-known options is Flashbots Protect, a service from the research organisation Flashbots that sends Ethereum transactions to block builders privately. Similar private endpoints are run by other groups, and some wallets now enable such routing by default.

Imagine posting a letter announcing that you are about to buy a large amount of something at the market. Anyone who reads the letter before it arrives could rush to buy first and sell to you at a higher price. MEV protection is like sending the letter in a sealed envelope straight to the person who runs the market, so nobody can read it along the way.

Another approach is to change the market itself, so that everyone who wants to trade in the same period is matched together at one fair price. When there is no line to jump, there is little to gain from reading other people's letters.

The need for protection grew with decentralised trading. Because public blockchains show pending transactions to anyone running a node, every swap on an automated market maker is visible before it is confirmed. Studies of Ethereum activity have found sandwich attacks affecting large numbers of ordinary trades, particularly on popular tokens and during volatile markets, and users frequently do not realise they have been targeted because the loss shows up only as a slightly worse price.

• Private transaction relays. Instead of broadcasting to the public mempool, the wallet sends the transaction through a protected endpoint, often called a protected RPC, directly to trusted block builders. Searchers cannot see it in advance, so they cannot sandwich it. Some services also share back part of any value from harmless back-running.
• Batch auctions and solvers. Exchanges using batch auctions collect orders over a short period and settle them at a single clearing price, often matching buyers and sellers directly. Specialist "solvers" compete to find the best execution.
• Intent-based trading. Users sign an intent describing the outcome they want, and competing fillers execute it, taking on the MEV risk themselves.
• Tight slippage limits. Setting a low maximum slippage limits how much a sandwich attack can take, at the cost of more failed trades.
• Protocol-level designs. Pools can include rules that capture or reduce MEV, for example through liquidity hooks, and researchers are working on encrypted mempools.

For most users, protection means choosing a wallet or exchange that offers it, or adding a protected network endpoint to a wallet such as MetaMask. Many DEX aggregators and decentralised exchanges route orders privately or through batch auctions by default. Large traders may also use request-for-quote systems in which market makers commit to a price before the trade is sent on-chain. On other networks, similar services exist; on Solana, much block-building activity runs through the Jito client, and some wallets there offer their own forms of protection.

Users can check whether a past trade was sandwiched by looking at the transactions immediately before and after it in a block explorer: a purchase of the same token just before the trade and a sale just after it, by the same address, is the typical sign.

• Trust. Private relays require trusting the relay and builders not to exploit or leak the transaction. Protection depends on their honesty and security.
• Inclusion speed. If only some builders receive a private transaction, it may take longer to be included than a public one.
• Partial coverage. Protection mostly guards against sandwiching and front-running of a user's own trade. It does not prevent losses from poor liquidity, bad prices or smart-contract risk.
• Centralisation. Routing more transactions through a few relays and builders concentrates power in the block production chain, which some researchers see as a risk to the network's neutrality.
• Costs and fees. Some services charge fees or keep a share of any refunds, and protected routes may not always give the best price.

Because MEV comes from the way blocks are built, user-side protection is only part of the answer. Longer-term proposals aim to reduce harmful MEV at the protocol level so that ordinary users do not need special tools to trade fairly, while still paying gas fees that reflect real network demand.

• Flashbots Protect documentation