ERC-20 token approval check on Base

$0.002 per call · failed calls are never charged · no account or API key needed

Check how much of a wallet's ERC-20 token a spender contract is approved to move on Base: the raw and formatted allowance, the token symbol and decimals, and whether the approval is unlimited. Use before a swap or deposit to see if an approve transaction is needed, and to audit a wallet for risky unlimited approvals.

Run it free (25 free calls) Buy credits by card (from $5) Example result (JSON)

Inputs

NameTypeDescription
token (required)stringERC-20 token contract address on Base (0x...)
owner (required)stringWallet address that holds the token (0x...)
spender (required)stringAddress allowed to spend, usually a router or protocol contract (0x...)

Request

Over HTTP, with a card key from /credits:

curl -H "Authorization: Bearer adt_…" "https://agent-data-tools.revmesh2074.workers.dev/base-allowance?token=0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913&owner=0x4200000000000000000000000000000000000006&spender=0x000000000022D473030F116dDEE9F6B43aC78BA3"

Or one of your 25 free calls, no key:

curl "https://agent-data-tools.revmesh2074.workers.dev/base-allowance?token=0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913&owner=0x4200000000000000000000000000000000000006&spender=0x000000000022D473030F116dDEE9F6B43aC78BA3&trial=1"

Without a key, the same URL answers 402 Payment Required with x402 and MPP terms, so an agent with a wallet pays per call in USDC (Base, Polygon, Arbitrum, Monad, World Chain or Tempo) and retries.

Example result

{
  "chain": "base",
  "token": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
  "symbol": "USDC",
  "decimals": 6,
  "owner": "0x4200000000000000000000000000000000000006",
  "spender": "0x000000000022D473030F116dDEE9F6B43aC78BA3",
  "allowance": "0",
  "allowanceFormatted": "0",
  "unlimited": false,
  "approved": false
}

From an AI agent (MCP)

Add the MCP server to Claude, Cursor or any MCP client. This tool is base_allowance, and the first 25 successful calls are free:

https://agent-data-tools.revmesh2074.workers.dev/mcp

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