# AgentIndex x402 Echo

> AgentIndex x402 Echo is a paid API for AI agents from x402.agentindex.world, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-02).

Validates x402 micropayment settlement by echoing the request back with payment confirmation details after a $0.000001 USDC payment on Base.

## Facts

- Endpoint: GET https://x402.agentindex.world/x402-echo?utm_source=zero.xyz
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/agentindex-x402-echo-310b6f82
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_afhEr0vmEcTkHtYUx-AEQ

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 agentindex-x402-echo-310b6f82
```

Example prompt: Send a quick test echo request to the AgentIndex x402 endpoint with message 'hello agent' to confirm my micropayment settlement is working correctly on Base mainnet.

## When to prefer this

Use this endpoint when you need to verify that your x402 micropayment integration is working end-to-end on Base mainnet at the absolute minimum cost ($0.000001 USDC). It is the canonical conformance test for the AgentIndex x402 protocol stack. Prefer this over other echo or health-check endpoints when you specifically need to confirm payment settlement, receipt generation, and payer address recognition in a single call.

## Known failure modes

- Payment not settled — returns 402 if USDC micropayment is not included or fails
- Invalid method — only GET, HEAD, DELETE are accepted
- Malformed queryParams — unrecognized fields rejected due to additionalProperties:false
- Insufficient balance — agent wallet lacks USDC on Base
- Network mismatch — payment sent on wrong chain returns settlement error

## How this service works

Cheapest possible Base-mainnet x402 conformance call: settle $0.001 of USDC and receive payer identity, request echo and receipt. Built for agents testing wallets, Payment-Signature, facilitators and settlement. Try GET /x402-echo/sample.

## Output

Returns a JSON object confirming settlement with: ok (boolean), payer wallet address, network identifier (eip155:8453 for Base), purpose string, echoed request object, price in USDC (0.000001), atomic price in USDC units, and the full x402 payment receipt.

## 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",
     "required": [],
     "properties": {
      "message": {
       "type": "string",
       "description": "Optional test message to echo after successful settlement."
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "required": [
      "ok",
      "purpose",
      "network",
      "price_usdc",
      "price_atomic_usdc",
      "request"
     ],
     "properties": {
      "ok": {
       "type": "boolean"
      },
      "payer": {
       "type": [
        "string",
        "null"
       ]
      },
      "network": {
       "type": "string"
      },
      "purpose": {
       "type": "string"
      },
      "request": {
       "type": "object"
      },
      "price_usdc": {
       "type": "number"
      },
      "x402_receipt": {
       "type": "object"
      },
      "price_atomic_usdc": {
       "type": "string"
      }
     }
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "ok": true,
  "payer": "0xb3F32bdfe8D07825BC0D7387295aB1D7559BA69d",
  "network": "eip155:8453",
  "purpose": "x402-mainnet-conformance",
  "request": {
   "echo": {
    "hello": "agent"
   },
   "method": "POST"
  },
  "price_usdc": 0.001,
  "price_atomic_usdc": "1000"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/agentindex-x402-echo-310b6f82/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402.agentindex.world](https://www.zero.xyz/host/x402.agentindex.world/llms.txt)