# Keystone Opportunity API – Base Wallet Lookup

> Keystone Opportunity API – Base Wallet Lookup is a paid API for AI agents from keystone-opportunity-api.keystone-opportunity.workers.dev, paid per call via x402, $0.02/call, status unknown (last checked 2026-09-13).

Fetches ETH and USDC balances, transaction count, and contract status for a given Base network wallet address, paid via x402/USDC onchain.

## Facts

- Endpoint: GET https://keystone-opportunity-api.keystone-opportunity.workers.dev/v1/base/wallet/%7Baddress%7D
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-13
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/keystone-opportunity-api-base-wallet-lookup-0667ccfc
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_aDr9Hy2M5yrQ2-K9MTrDb

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 keystone-opportunity-api-base-wallet-lookup-0667ccfc
```

Example prompt: What are the current ETH and USDC balances for the Base wallet 0x1234567890abcdef1234567890abcdef12345678, and is it a contract address?

## When to prefer this

Choose this endpoint when you need a fast, no-API-key, onchain-settled lookup of ETH and USDC balances plus contract/EOA status for a Base network address. Ideal for autonomous agents that already operate within the x402 payment ecosystem and need deterministic, programmatic wallet data without managing API subscriptions.

## Known failure modes

- Invalid or malformed wallet address returns an error or empty result
- Address not yet active on Base (zero transactions) may return zeroed balances
- Network congestion or RPC issues may cause stale or delayed data
- x402 payment failure (insufficient USDC, wrong facilitator) blocks the request
- Cloudflare Worker timeout on high-load periods

## How this service works

Low-cost, deterministic x402 utilities for autonomous agents on Base. Every /v1 route is priced in USDC and settles onchain via the x402 protocol; discover and pay programmatically through the x402 Bazaar. No API keys, no subscriptions.

## Output

Returns a JSON object containing the wallet's ETH balance (float), USDC balance (float), the queried address, chain ID (8453 for Base), network name ('base'), a boolean indicating whether the address is a smart contract, the transaction count, and the timestamp of observation.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "properties": {
   "type": "string"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "eth": 0.0123,
  "usdc": 4.77,
  "address": "0x0000000000000000000000000000000000000000",
  "chainId": 8453,
  "network": "base",
  "contract": false,
  "observedAt": "2026-07-26T00:00:00.000Z",
  "transactionCount": 12
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/keystone-opportunity-api-base-wallet-lookup-0667ccfc/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from keystone-opportunity-api.keystone-opportunity.workers.dev](https://www.zero.xyz/host/keystone-opportunity-api.keystone-opportunity.workers.dev/llms.txt)