What is MEV?
MEV, maximal extractable value, is the profit available to whoever decides the order of transactions in a block. On Ethereum, a swap you send through a regular RPC waits in the public mempool before a block builder includes it. Anyone can read it there: the tokens, the amount and the minimum you accept.
Bots called searchers watch the mempool and pay builders to place their own transactions right before or right after yours. Some of that activity is harmless arbitrage. Some of it comes straight out of your trade.
| Type | What the bot does | Who pays |
|---|---|---|
| Sandwich attack | Buys just before your swap and sells just after it, so you trade at a price the bot pushed up. | Direct: you receive less, down to your minimum. |
| Front-running | Copies or pre-empts a profitable transaction it sees pending, paying more to land first. | Direct: you get a worse price, or the opportunity is gone. |
| Back-running | Lands right after your trade to arbitrage the price gap it created between pools. | Indirect: it does not change your execution price. |
| Just-in-time liquidity | Adds concentrated liquidity right before a large swap and removes it right after. | Mostly to other liquidity providers, who lose the fees. |
How a sandwich attack works
A sandwich is three transactions in the same block, with yours in the middle. The bot needs two things: a pool your swap will move, and enough room between the quoted price and your minimum to make a profit after gas.
Front-run
The bot sees your pending buy and buys the same token first, with a higher priority fee. The pool price rises from 2,400 to 2,412.
Your swap
Your trade executes on the moved pool, at a worse average price. It still succeeds, because the result is above your minimum received.
Back-run
The bot sells what it bought into the higher price your trade created, and keeps the gap minus gas and builder tips.
What ChainBridge does about it
No swap interface can make MEV disappear. What it can do is shrink the room a bot has to work with and refuse to send a transaction that would fail.
Sized slippage
Auto mode starts at 0.05% for stablecoin pairs, 0.3% for major pairs and 1% for other tokens, plus half the price impact, capped at 3%. A custom value above 2% shows a front-running warning.
Minimum fixed in what you sign
Every route carries a minimum amount out. If the price is pushed below it, the transaction reverts instead of filling at a worse price.
Gasless orders
On supported networks, a gasless swap is a signed order that 0x's relayer submits for you. The minimum you receive is part of the signed order. See the gasless trading guide.
Market-maker fills
Through 0x, part of a route can be filled by a professional market maker at a fixed, signed price rather than from a pool curve, which a front-run on the pool does not move.
The review screen also simulates the exact transaction before you sign, and blocks the swap if it would revert. Simulation runs on the current state of the chain, so it cannot predict a sandwich that happens later, but it stops you from paying gas for a trade that cannot succeed. Read transaction simulation for details.
MEV risk by network
How exposed you are depends on how the network orders transactions. Chains with a public mempool let bots see and bracket your trade; rollups with a single sequencer mostly do not.
| Network | Ordering | Sandwich exposure |
|---|---|---|
| Ethereum | Public mempool, block builders order transactions | Highest: sandwich bots are active on every liquid pair |
| BNB Chain, Polygon, Avalanche | Public mempool, validator-ordered | Real: sandwiching is common on popular tokens |
| Arbitrum, Base, Optimism, Linea | Single sequencer, no public mempool | Lower: classic sandwiches are hard, but tight slippage still matters |
The same trade on a layer 2 is also far cheaper in gas. If your tokens already live there, it is usually the better place to swap. See layer 2 networks.
Checklist: protect your swaps
Keep slippage on auto
Set a custom tolerance only for the trade that needs it, such as a token with a transfer tax, and switch back afterwards.
Check the minimum received
Before signing, read the minimum on the review screen. That number, not the expected amount, is your worst case.
Use a private RPC for large trades on Ethereum
Services such as Flashbots Protect or MEV Blocker send your transaction straight to block builders instead of the public mempool. You add them as a custom network RPC in your wallet; they work with any app, including ChainBridge.
Split very large orders
A single large swap leaves more value to extract. Several smaller swaps over a few blocks each offer less, at the cost of more gas.
Be careful in fast markets
During sharp moves, quotes go stale quickly. Refresh the quote rather than raising your tolerance to force a trade through.
Where MEV protection is heading
The wider industry is moving away from broadcasting raw swaps. Intent-based systems such as UniswapX and CoW Protocol let you sign the result you want and leave execution to competing solvers, and batch auctions settle many orders at one price. Encrypted mempools aim to hide transaction contents until they are ordered.
These are general industry developments, not ChainBridge features today. On ChainBridge, the protections that apply now are the ones above: a tight, sized minimum, gasless orders where available, and a simulation before every swap.