# Ethereum ERC-20 Allowance Lookup

> Ethereum ERC-20 Allowance Lookup is a paid API for AI agents from api.arysphere.com, paid per call via x402, $0.002/call, status unknown (last checked 2026-10-17).

Returns the raw ERC-20 token allowance a holder (owner) has granted to a spender on Ethereum mainnet.

## Facts

- Endpoint: GET https://api.arysphere.com/v1/ventures/x402_eth_reads_v1/eth_mainnet_erc20_allowance?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-17
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/ethereum-erc-20-allowance-lookup-71ddcb87
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_fXQpovXmvoDZN9RwC_Ogs

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability ethereum-erc-20-allowance-lookup-71ddcb87
```

Example prompt: What's the current ERC-20 allowance that wallet 0xAbCd...1234 (owner) has approved for the Uniswap v2 router 0x7a25...5678 to spend on the USDC contract 0xA0b8...eB48 on Ethereum mainnet?

## When to prefer this

Use this endpoint when you need to read the current ERC-20 allowance on Ethereum mainnet for a specific owner-spender-token triple without writing any transaction. It is ideal for pre-trade checks, approval auditing, and DeFi automation flows where you need the raw uint256 value directly from the contract. Prefer this over general blockchain RPC calls when you want a simple, pay-per-use HTTP GET with no node infrastructure setup required.

## Known failure modes

- Invalid address format (owner, token, or spender not matching 0x + 40 hex pattern) returns validation error
- Token contract address is not a valid ERC-20 contract, causing a revert or zero return
- Ethereum node unavailability or RPC timeout causes failure
- Missing required query parameters (token, owner, spender) results in bad request error
- Payment failure (insufficient USDC balance or x402 protocol error) blocks the request

## How this service works

ARYSPHERE sells AI-written verdicts on Base token contracts (a grade, a one-liner, a roast and the contract's facts) and Base/Ethereum chain reads, paid per call in USDC on Base over x402 v2. No account and no API key.

## Output

A JSON object containing a boolean 'ok' field, the chain identifier, the method used, the service name, and most importantly 'result' — the uint256 allowance as a decimal string representing the raw token units approved by the owner for the spender. On failure, an 'error' field is included instead.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "owner": {
       "type": "string",
       "pattern": "^0x[0-9a-fA-F]{40}$",
       "description": "0x + 40 hex"
      },
      "token": {
       "type": "string",
       "pattern": "^0x[0-9a-fA-F]{40}$",
       "description": "ERC-20 contract, 0x + 40 hex"
      },
      "spender": {
       "type": "string",
       "pattern": "^0x[0-9a-fA-F]{40}$",
       "description": "0x + 40 hex"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "ok": true,
  "chain": "ethereum",
  "method": "allowance",
  "result": "0",
  "service": "x402_eth_reads_v1.eth_mainnet_erc20_allowance"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/ethereum-erc-20-allowance-lookup-71ddcb87/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.arysphere.com](https://www.zero.xyz/host/api.arysphere.com/llms.txt)