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MEV searchers on Ethereum use the eth_sendBid method to participate in BlockRazor’s orderflow auction by attaching a bid denominated in wei to a bundle targeting a specific signal transaction. The searcher workflow is built around speed and precision: monitor the mempool for profitable signal transactions, construct a backrun bundle that captures the resulting opportunity, calculate a bid that remains below the expected profit, and submit before the auction closes. The highest bidder for each signal transaction wins exclusive placement immediately after it in the target block.
The Ethereum Searcher Bundle service is available to all new registered users with no rate limits. For Private Mempool access—which provides signal transactions before public propagation—see the Pricing page.

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Endpoint

POST https://bundle.blockrazor.io/ethereum
Authentication is performed via a Bearer token passed in the Authorization header.

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MEV Searcher Workflow

The typical searcher cycle for Ethereum orderflow auctions consists of four stages:
  1. Detect — Subscribe to BlockRazor’s Mempool Stream or Private Mempool feed. When a signal transaction matching your strategy criteria appears, capture its hash and simulate its on-chain effect.
  2. Build — Construct one or more signed backrun transactions that profitably exploit the state change created by the signal transaction (e.g., arbitraging a resulting price imbalance).
  3. Bid — Calculate the maximum bid you can pay while still extracting positive profit. Submit the bundle via eth_sendBid with that bid value.
  4. Confirm — After the target block is sealed, verify that your bundleHash appears on-chain to confirm a successful auction win.
Private Mempool access delivers BlockRazor’s RPC orderflow to your system before it reaches public nodes, giving your simulation and bidding pipeline a meaningful head start over searchers relying on public mempool data.

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Request

The request follows the standard JSON-RPC 2.0 envelope. The single element of params is a bundle-bid object with the fields described below.

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Bundle Parameters

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txs
string[]
required
An ordered array of signed raw transactions encoded as hex strings (each prefixed with 0x). These are the searcher’s backrun transactions. They execute sequentially and atomically immediately after the signal transaction if the bid wins the auction.
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blockNumber
string
required
The target block number for bundle inclusion, expressed as a hex string (e.g., "0x12A05F0"). The bid is only active for this specific block; if the block passes without inclusion, the bundle is discarded.
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bid
string
required
The amount in wei that the searcher offers for the backrun slot, expressed as a hex string (e.g., "0x2386F26FC10000" for 0.01 ETH). The highest bid among all competing submissions for the same signalTx wins the auction.
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signalTx
string
required
The transaction hash of the signal transaction to follow. This identifies the auction slot being bid on and determines where in the block the winning bundle will be placed.

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Code Examples

curl -X POST https://bundle.blockrazor.io/ethereum \
  -H 'Content-Type: application/json' \
  -H 'Authorization: Bearer YOUR_AUTH_TOKEN' \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_sendBid",
    "params": [
      {
        "txs": ["0xBACKRUN_TX_1", "0xBACKRUN_TX_2"],
        "blockNumber": "0x12A05F0",
        "bid": "0x2386F26FC10000",
        "signalTx": "0xSIGNAL_TX_HASH"
      }
    ],
    "id": 1
  }'

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Response

A successful submission returns a bundleHash that registers your bid in the auction. A valid response does not guarantee inclusion—a higher competing bid may win the slot.
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bundleHash
string
The unique hash of the submitted bid bundle. Use this to verify post-block whether your bundle was included in the target block.
Response Example
{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "bundleHash": "0x1a2b3c4d5e6f..."
  }
}

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Bid Strategy Guidance

Setting the right bid is the core challenge for searchers. Bid too low and a competitor wins the slot; bid too high and the trade becomes unprofitable.
Always simulate the full bundle—including the signal transaction—before submitting to verify that your backrun transactions are profitable under the expected post-signal state. On-chain conditions can change between detection and block inclusion, so build a margin of safety into your profit estimate before setting the bid.

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