MEV builder share

Builder market share aggregated over the last N MEV-Boost blocks via the Flashbots relay. Send POST /api/mev-builder-share with no required fields (1 optional) and pay $0.002 per call over x402 or MPP (there is no free tier). It returns a JSON object with windowBlocks, uniqueBuilders, relay and builders.

Returns per-builder block count, share percent, total ETH paid to proposers, and average per block. Use to track block-builder concentration or detect a new builder gaining share.

Category: Crypto & onchain data · Tags: mev flashbots builder-share concentration market-structure

TRY IN PLAYGROUND →

Parameters

Example request

curl -i -X POST https://agent402.tools/api/mev-builder-share \
  -H "Content-Type: application/json" \
  -d '{"window":100}'

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

Example response

{
  "windowBlocks": 100,
  "uniqueBuilders": 5,
  "relay": "flashbots",
  "builders": [
    {
      "builderPubkey": "0x9000...",
      "builderShort": "0x90000000…abcdef",
      "blocks": 42,
      "sharePct": 42,
      "totalEthToProposers": 3.456789,
      "avgEthPerBlock": 0.082305
    }
  ]
}

From an MCP client

catalog.call {
  "slug": "mev-builder-share",
  "params": {
    "window": 100
  }
}

The hosted connector at https://agent402.tools/mcp needs a payment for mev-builder-share; 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-builder-share 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-builder-share", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "window": 100
  }),
});

Related tools