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How to send backrun bundles to MEV Blocker RPC

N.B. Historical submitted bundles, including those that did not land on-chain, will not only be shared with builders but also archived and presented to the public for transparency

  1. Connect to the websocket server located at
websocat wss://
  1. Use the eth_subscribe method to subscribe to unsigned pending transactions - mevblocker_partialPendingTransactions:
{"method":"eth_subscribe","params": ["mevblocker_partialPendingTransactions"]}


{"jsonrpc": "2.0", "id": 1, "result": "0xd58bbbc0f5190962eff01b6f0ec17724"}
  1. You'll start receiving unsigned pending transactions (missing v, r, and s):
{"jsonrpc": "2.0", "method": "eth_subscription", "params": {"subscription": "0xd58bbbc0f5190962eff01b6f0ec17724", "result": {"chainId": "0x1", "to": "0x6215589d293fdf52886484f46f0d6a11c76b4a7e", "value": "0x4fefa17b724000", "data": "0x", "accessList": [], "nonce": "0x10", "maxPriorityFeePerGas": "0x0", "maxFeePerGas": "0x7e1c65b04", "gas": "0x5208", "type": "0x2", "hash": "0x5f08dd372fce1a44dda27bed60ca036acb4979fad6ca37b9c388e351a870fe4c", "from": "0xcb1588f3f7e92a1278c68a6aed4bdcbc68534b29"}}}
  1. Construct a back-run bundle just like you would for a target transaction from the mempool, but make the first element of the txs array in params of eth_sendBundle the hash of the pending target, instead of the fully-encoded transaction

N.B. The pending target transaction must be the first transaction in txs, and only one target transaction can be included per bundle, otherwise the request will be rejected. It is still possible to submit multiple bundles for the same block, containing different target transactions.

  1. Send the back-run bundle to the same websocket connection using the eth_sendBundle method

N.B replacementUuid is supported in this version of eth_sendBundle

  "jsonrpc": "2.0",
  "id": 1,
  "method": "eth_sendBundle",
  "params": [
      "txs": [
        // this is the 32-byte transaction hash of the target transaction
        // this is your signed encoded transaction
      "blockNumber": "0xb63dcd",
      "minTimestamp": 0,
      "maxTimestamp": 1615920932