ERC-20 allowance (owner to spender)

How much of an ERC-20 token a spender contract is approved to move from an owner wallet - the approval check an agent runs before a swap, a bridge, or an x402 transferWithAuthorization flow. Send POST /api/token-allowance with the required fields contract, owner and spender and pay $0.002 per call over x402 or MPP (there is no free tier). It returns a JSON object with network, chainId, contract, owner, spender and 7 more.

Returns the allowance as an exact decimal string scaled by the token's decimals, the raw uint256, and an `unlimited` flag for max-uint style approvals.

Category: Crypto & onchain data · Tags: crypto erc20 allowance approval approve spender wallet evm · Also found as: allowance

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Parameters

Example request

curl -i -X POST https://agent402.tools/api/token-allowance \
  -H "Content-Type: application/json" \
  -d '{"contract":"0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48","owner":"0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045","spender":"0x3fC91A3afd70395Cd496C647d5a6CC9D4B2b7FAD","network":"ethereum"}'

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

Example response

{
  "network": "ethereum",
  "chainId": 1,
  "contract": "0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48",
  "owner": "0xd8da6bf26964af9d7eed9e03e53415d37aa96045",
  "spender": "0x3fc91a3afd70395cd496c647d5a6cc9d4b2b7fad",
  "symbol": "USDC",
  "decimals": 6,
  "allowance": "0",
  "raw": "0",
  "unlimited": false,
  "source": "alchemy",
  "fetchedAt": "2026-08-22T12:00:00.000Z"
}

From an MCP client

catalog.call {
  "slug": "token-allowance",
  "params": {
    "contract": "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
    "owner": "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
    "spender": "0x3fC91A3afd70395Cd496C647d5a6CC9D4B2b7FAD",
    "network": "ethereum"
  }
}

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

Errors and behavior

• contract, owner and spender are 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/token-allowance 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/token-allowance", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "contract": "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
    "owner": "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
    "spender": "0x3fC91A3afd70395Cd496C647d5a6CC9D4B2b7FAD",
    "network": "ethereum"
  }),
});

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