# ERC-20 Token Allowance Lookup (Optimism)

> ERC-20 Token Allowance Lookup (Optimism) is a paid API for AI agents from saylorinnovations.com, paid per call via x402, $0.002/call, status unknown (last checked 2026-09-30).

Returns the ERC-20 token allowance granted by a token holder to a spender on the Optimism network

## Facts

- Endpoint: GET https://saylorinnovations.com/api/evm/optimism/allowance/:address/:address2/:address3?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-30
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/erc-20-token-allowance-lookup-optimism-99d2be44
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_8Y2ZHerYx6Ja5iuxhT-lJ

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 erc-20-token-allowance-lookup-optimism-99d2be44
```

Example prompt: Check the ERC-20 allowance on Optimism for token contract 0x4200000000000000000000000000000000000042, where the owner is 0xAbCd...1234 and the spender is 0xDeFi...5678 — I want to know how many tokens that spender is approved to use.

## When to prefer this

Use this endpoint when you specifically need to query ERC-20 token allowances on the Optimism L2 network. Prefer this over generic RPC calls when you need a simple, pay-per-call REST API without managing your own Optimism node or RPC credentials. Ideal for agents that need to verify DeFi approval states, audit token permissions, or gate actions on whether a contract has sufficient spending approval on Optimism.

## Known failure modes

- Invalid or malformed Ethereum address returns an error or zero allowance
- Contract address is not a valid ERC-20 token contract — call may fail or return unexpected data
- Network connectivity issues to Optimism RPC nodes may cause timeouts
- Allowance is zero if the owner has never approved the spender — not an error, but a valid zero result
- Rate limiting or payment failure may block the request

## How this service works

ERC-20 Allowance (optimism). Optimism ERC-20 allowance: how much a spender may move from an owner, human-readable, with an unlimited-approval flag.

## Output

Returns the numeric allowance amount (in the token's base units) that a spender address is permitted to transfer on behalf of the owner address for the specified ERC-20 token contract on the Optimism network. Typically includes the raw allowance value as a big integer.

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/erc-20-token-allowance-lookup-optimism-99d2be44/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from saylorinnovations.com](https://www.zero.xyz/host/saylorinnovations.com/llms.txt)