# x402 Preflight Checker

> x402 Preflight Checker is a paid API for AI agents from email-preflight-api.vercel.app, paid per call via x402, $0.003/call, status unknown (last checked 2026-10-17).

Inspects a live x402 v2 payment challenge before an agent commits to payment, verifying price, network, payee, resource binding, timeout, and Bazaar metadata without paying or forwarding credentials.

## Facts

- Endpoint: POST https://email-preflight-api.vercel.app/api/x402-preflight?utm_source=zero.xyz
- Price: $0.003/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-17
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402-preflight-checker-2b748e5c
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap__O9RRPQSj56e9iG1JO10f

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 x402-preflight-checker-2b748e5c -d '<json body>'
```

Example prompt: Before I pay that x402-protected endpoint, can you run a preflight check on it to verify the price, payee address, network, and resource binding without actually spending anything?

## When to prefer this

Use this endpoint whenever an AI agent is about to pay an unfamiliar or untrusted x402-protected resource and needs to verify payment terms, payee identity, and metadata before committing funds. It is specifically designed for the x402 v2 protocol and Bazaar marketplace context, making it the right choice over generic HTTP inspection tools when payment safety and protocol compliance are the concern.

## Known failure modes

- Target URL unreachable or returns non-x402 response
- x402 challenge version mismatch (not v2)
- Challenge already expired at time of probe
- Malformed or missing Bazaar metadata fields
- Network timeout on preflight probe
- Target endpoint returns unexpected status code

## How this service works

Pre-action check for AI agents: inspect an unfamiliar live x402 v2 challenge immediately before purchase. Verify price, network, payee, resource binding, timeout, and Bazaar metadata without paying the target or forwarding credentials. POST probes send only a fixed empty JSON object; callers cannot supply target request content.

## Output

Returns structured details about the x402 v2 challenge: the required payment price and currency, target network, payee address, resource binding confirmation, challenge timeout, and any Bazaar metadata — all without triggering a payment or exposing caller credentials.

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/x402-preflight-checker-2b748e5c/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from email-preflight-api.vercel.app](https://www.zero.xyz/host/email-preflight-api.vercel.app/llms.txt)