Farcaster by Ethereum address

Reverse-lookup an Ethereum address to its Farcaster account (via verified address). Send POST /api/farcaster-by-address with the required field address and pay $0.002 per call over x402 or MPP (there is no free tier). It returns a JSON object with found, address, fid, username, displayName and 6 more.

Returns FID, username, display name, bio, follower/following counts, and Warpcast URL, or found=false if the address has not verified on Farcaster. Use to label wallet activity with the owner's Farcaster identity when ENS is missing.

Category: Crypto & onchain data · Tags: farcaster warpcast identity reverse-lookup verification

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Parameters

Example request

curl -i -X POST https://agent402.tools/api/farcaster-by-address \
  -H "Content-Type: application/json" \
  -d '{"address":"0xd7029bdea1c17493893aafe29aad69ef892b8ff2"}'

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

Example response

{
  "found": true,
  "address": "0xd7029bdea1c17493893aafe29aad69ef892b8ff2",
  "fid": 3,
  "username": "dwr",
  "displayName": "Dan Romero",
  "pfpUrl": "https://...",
  "bio": "Working on Farcaster.",
  "followerCount": 500000,
  "followingCount": 1000,
  "venueUrl": "https://warpcast.com/dwr",
  "source": "neynar"
}

From an MCP client

catalog.call {
  "slug": "farcaster-by-address",
  "params": {
    "address": "0xd7029bdea1c17493893aafe29aad69ef892b8ff2"
  }
}

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

Errors and behavior

• address is required. An input the tool rejects returns an HTTP 4xx whose body carries error, tool, expected, required and example, so the caller can correct it.
• 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/farcaster-by-address 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/farcaster-by-address", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "address": "0xd7029bdea1c17493893aafe29aad69ef892b8ff2"
  }),
});

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