MEV block payment lookup

Look up the MEV-Boost payment for a specific slot or block number via the Flashbots relay. Send POST /api/mev-block-payment with no required fields (2 optional) and pay $0.002 per call over x402 or MPP (there is no free tier). It returns a JSON object with found, slot, blockNumber, blockHash, builderPubkey and 9 more.

Returns the builder, proposer, value paid in ETH, gas usage, and tx count. Returns found=false if the block was built locally or via a different MEV-Boost relay (Flashbots is one of several).

Category: Crypto & onchain data · Tags: mev flashbots block-payment lookup

TRY IN PLAYGROUND →

Parameters

Example request

curl -i -X POST https://agent402.tools/api/mev-block-payment \
  -H "Content-Type: application/json" \
  -d '{"blockNumber":26104983}'

Without payment this returns HTTP 402 Payment Required with the exact price for mev-block-payment; any x402 v2 or MPP client pays it and retries.

Example response

{
  "found": true,
  "slot": 15343686,
  "blockNumber": 26104983,
  "blockHash": "0x29b12476c4bdbad3d080057a7c068c42da781d4bfb1545491d65b9f942a20461",
  "builderPubkey": "0x89057b5818abfca92fb9d38ea74dfab0f6f58630b6138e4f73da26666295e047cb18d353a134c5fad672eba231ff610c",
  "builderShort": "0x89057b58…ff610c",
  "proposerPubkey": "0xb6ab19ca47a0b0f67e95e4cbb772fd8feff2a4f481eb494a06d54308f7fa959ee87889e2ffbe34ee8d466ed47a7d5dbd",
  "proposerFeeRecipient": "0xd4E96eF8eee8678dBFf4d535E033Ed1a4F7605b7",
  "valueWei": "9667520599769125",
  "valueEth": 0.009667520599769124,
  "gasUsed": 14100104,
  "gasLimit": 60000000,
  "numTx": 144,
  "relay": "flashbots"
}

From an MCP client

catalog.call {
  "slug": "mev-block-payment",
  "params": {
    "blockNumber": 26104983
  }
}

The hosted connector at https://agent402.tools/mcp needs a payment for mev-block-payment; the stdio package pays it from a wallet or from AGENT402_CREDITS_KEY. Local install: npx -y agent402-mcp.

Errors and behavior

• Every field is optional. An input the tool rejects returns an HTTP 4xx whose body carries error, tool, expected, required and example.
• A paid call that ends in any status of 400 or above is not charged over x402, MPP or a prepaid credits key: settlement is cancelled when the tool fails. The exception is a Tempo push credential, a transfer the buyer sent before the call: it settles before the tool runs, so if the tool then fails the payment is recorded as a refund owed to the paying wallet.
• Wallet-only: this tool reaches the network or stored state, so it has no proof-of-work tier. A prepaid card-credits key issued earlier (Authorization: Bearer a402_...) also pays it.
• A GET or HEAD to /api/mev-block-payment returns the same 402 quote, so the price can be read without a body.
• An Idempotency-Key header makes a retried paid call replay the first 200 instead of charging again (an answer larger than 1 MB is not replayed).

Paid call (JavaScript agent)

import { wrapFetchWithPayment } from "@x402/fetch";
import { x402Client } from "@x402/core/client";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const client = new x402Client();
client.setSpendControls?.(false); // keep your own spending ceiling in code
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://agent402.tools/api/mev-block-payment", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "blockNumber": 26104983
  }),
});

Related tools