# hello-world-x402 Echo Endpoint

> hello-world-x402 Echo Endpoint is a paid API for AI agents from hello-world-x402.vercel.app, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-14).

Returns the submitted payload verbatim (message, metadata, priority) after a $0.001 USDC micropayment on Base (eip155:8453)

## Facts

- Endpoint: POST https://hello-world-x402.vercel.app/echo
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/hello-world-x402-vercel-app-00dd0b29
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_K30zRrxb86343jcRYJSsj

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 hello-world-x402-vercel-app-00dd0b29 -d '<json body>'
```

Example prompt: Echo back the message 'Hello from my agent' with metadata 'test-run-1' and priority level medium — this is a paid echo test using USDC on Base.

## When to prefer this

Use this endpoint when you need to test or demonstrate the x402 micropayment protocol on the Base network (eip155:8453) with a trivial, side-effect-free operation. Ideal for integration testing of payment flows, verifying that USDC micropayments of $0.001 work end-to-end, or confirming payload integrity through a paid API boundary.

## Known failure modes

- Payment not provided or incorrect amount — 402 Payment Required response
- Payment on wrong network (not eip155:8453) — payment rejected
- Request exceeds 300 second timeout — timeout error
- Message exceeds 1000 character maxLength — validation error
- Metadata exceeds 200 character maxLength — validation error
- Invalid priority enum value — schema validation error

## How this service works

Returns the submitted payload verbatim after a required exact USD Coin payment on network eip155:8453 (max timeout 300s).

## Output

The exact submitted payload returned verbatim: the message string, metadata string, and priority enum value, unchanged from input.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "message": {
   "type": "string",
   "maxLength": 1000,
   "description": "Message to echo - UPDATED max length"
  },
  "metadata": {
   "type": "string",
   "maxLength": 200,
   "description": "Additional metadata - NEW FIELD"
  },
  "priority": {
   "enum": [
    "low",
    "medium",
    "high",
    "critical",
    "urgent"
   ],
   "type": "string",
   "description": "Priority level - ADDED critical and urgent"
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/hello-world-x402-vercel-app-00dd0b29/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from hello-world-x402.vercel.app](https://www.zero.xyz/host/hello-world-x402.vercel.app/llms.txt)