MEVDAO

Flashbots Protect vs MEV Blocker: Which Private RPC Should You Use?

By Merunas Grincalaitis · · 5 min read · 0 views

If you only change one setting in your Ethereum wallet this year, change the RPC. Swapping through the default public RPC means every transaction you send goes to the public mempool, where sandwich bots can see it before it lands. A private RPC sends it straight to block builders instead.

The two names that come up every time are Flashbots Protect and MEV Blocker. Both are free, both take about thirty seconds to set up, and both protect you from frontrunning. But they make different trade-offs, and the defaults aren't the same. Here's what actually matters.

One note before we start: these settings change over time. Everything below is from the official Flashbots Protect docs and mevblocker.io as of today. Check them before you rely on a specific detail.

What both of them do

The basic idea is the same:

  • Your wallet sends eth_sendRawTransaction to their RPC instead of a public node.
  • Your transaction is not broadcast to the public mempool.
  • They forward it to block builders, who can include it but can't (by the rules of the service) let searchers frontrun or sandwich it.
  • Searchers can still backrun it, which doesn't hurt you, and part of what they pay comes back to you as a refund.

That last point is the clever part. When your swap moves a pool's price, there's an arbitrage opportunity right after it. Normally some bot takes it and you get nothing. With these RPCs, searchers bid for the right to backrun, and you get a cut of the bid.

Flashbots Protect

Setup: add https://rpc.flashbots.net as a custom network in your wallet.

From the settings guide, the default configuration:

  • Forwards your transaction to the Flashbots builder.
  • Retries it for 25 blocks, then drops it if it didn't land.
  • Shares only the transaction hash plus a limited set of swap logs with searchers on MEV-Share.
  • Sends 90% of MEV refunds to tx.origin (you), and 10% to the validator.
  • Sends gas fee refunds to you too.
  • Won't land reverted transactions, so a failed swap doesn't cost you gas.

Then there's the /fast endpoint, https://rpc.flashbots.net/fast, which shares your transaction with all registered builders. That usually means faster inclusion. The trade-off, per the docs, is that validators get a bigger slice of the refund, and searchers running inside trusted execution environments (TEEs) get to see the full transaction (without signature) to find better backruns.

What I like about Protect is how configurable it is. Everything is a URL parameter:

  • ?hint=hash gives you maximum privacy. Only the hash is shared, so there's basically nothing to backrun, and less refund.
  • More hints, like hint=calldata&hint=logs&hint=function_selector&hint=contract_address, share more data, so searchers can find more backruns and you can earn a bigger refund. The MEV refunds page explains this trade-off.
  • builder= lets you add specific builders. More builders means faster inclusion, but you're trusting each of them.
  • refund=address:percent sends refunds to a different address.
  • canRevert=true lets failed transactions land, if you'd rather get fast feedback than save gas.
  • blockRange= changes the 25-block window.

MEV Blocker

Setup: add https://rpc.mevblocker.io as a custom network.

MEV Blocker is built and maintained by CoW Protocol, Agnostic Relay and Beaver Build. It sends your transaction to a network of searchers who can bid to backrun it but can't frontrun or sandwich it. When a searcher wins, MEV Blocker splits the bid 90/10 between you and the validator, paid to tx.origin in the same block. According to its FAQ, it submits to all the major builders.

Instead of query parameters, it has five endpoints:

  • /fast (the default): frontrunning protection and refunds, but no revert protection.
  • /noreverts: same, plus revert protection.
  • /fullprivacy: maximum privacy and revert protection, no rebates.
  • /maxbackruns: optimized for backrun opportunities, with refunds and revert protection.
  • /nochecks: maximum protection, no rebates, no revert protection.

The differences that matter in practice

Failed transactions

This is the one people miss. Flashbots Protect's default won't land reverted transactions. If your swap would fail, you don't pay gas for it.

MEV Blocker's default (/fast) does not protect against reverts. If you want that, use https://rpc.mevblocker.io/noreverts. For normal people swapping on DEXs, I'd honestly just use /noreverts.

Speed

Default Protect goes to the Flashbots builder only. That builder doesn't build every block, so you may wait a few blocks. Protect's /fast and MEV Blocker's default both send to many builders, so they tend to land quicker.

For time-sensitive stuff, pick a multi-builder option.

Privacy vs refunds

Both make you choose. Share more information and searchers can backrun you better, so you get more back. Share less and you're more private but earn less.

  • Max privacy: Protect with ?hint=hash, or MEV Blocker /fullprivacy.
  • Max refunds: Protect with all hints, or MEV Blocker /maxbackruns.

Configurability

Protect wins here. You can pick builders, hints, refund addresses, block range and revert behaviour. MEV Blocker gives you five sensible presets. Most people don't need more than that.

What neither of them does

  • They don't replace slippage settings. MEV Blocker's FAQ is blunt about it: always set slippage, because no solution gives 100% protection, and a small share of transactions can become public, for example after a reorg.
  • They don't protect you from bad tokens. If you buy a honeypot through a private RPC, you still own a honeypot.
  • They don't make you trustless. You're trusting the RPC operator and the builders it forwards to not to leak or abuse your transaction. Both projects are reputable and well known, but it's still trust.
  • They're not for bots. If you're running a searcher or a sniper, you don't want refunds or 25-block retries. You want bundles sent to builders for a specific block, with exact ordering. That's a different tool, which I covered in Flashbots bundles explained.

So which one should you use?

My take:

  • You just want to swap safely and not think about it: MEV Blocker /noreverts, or Flashbots Protect /fast. Both are multi-builder, private, and give refunds. Turn on revert protection with MEV Blocker.
  • You're moving a lot of money and privacy matters most: Flashbots Protect with ?hint=hash, or MEV Blocker /fullprivacy.
  • You want to tune everything: Flashbots Protect, because of the URL parameters.
  • You're rescuing a compromised wallet: neither as a regular RPC. You need an atomic bundle. Flashbots Protect has a bundle mode for whitehat rescues, but for a wallet with an active sweeper, use a proper rescue flow. See how to rescue tokens from a compromised wallet.

Honestly, the difference between the two is much smaller than the difference between using either of them and using none. Pick one today.

Setting it up in your wallet

In most wallets it works the same way:

  1. Go to networks and add a custom network (or edit Ethereum Mainnet's RPC).
  2. Network name: anything you want, like "Ethereum (Protected)".
  3. RPC URL: one of the URLs above.
  4. Chain ID: 1. Currency: ETH. Explorer: https://etherscan.io.
  5. Make sure the new network is selected before you swap. Some wallets switch back silently.

If you're sniping new tokens, where you need to be in a specific block rather than "sometime soon, privately", the MEVDAO Sniper Bot uses Flashbots bundles for that. It's part of the subscription, with a 3-day free trial.

For more, join the MEV Secrets email list below, or message me on Telegram.

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