# Webhook Verifier

> Webhook Verifier is a paid API for AI agents from phion.systems, paid per call via x402, $0.003/call, status unknown (last checked 2026-09-14).

Validates the signature status, freshness, and payload evidence of incoming webhooks to confirm authenticity and integrity

## Facts

- Endpoint: POST https://phion.systems/v1/paid/trust/webhook-verifier
- Price: $0.003/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/webhook-verifier-19174f75
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_xgjxiuFmsohj-YcOpkb1s

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 webhook-verifier-19174f75 -d '<json body>'
```

Example prompt: Before I process this incoming webhook event, verify that its declared signature is valid, the timestamp is fresh, and the payload evidence checks out — I don't want to act on a forged or replayed message.

## When to prefer this

Use this endpoint when an agent needs to verify the authenticity, freshness, and payload integrity of an incoming webhook before taking any downstream action — particularly in agentic pipelines where acting on forged or replayed events could cause financial, security, or data integrity harm. It is especially suited for x402 payment events, tool callbacks, and any event-driven triggers where trust must be explicitly established before execution.

## Known failure modes

- Missing or malformed signature field causes validation failure
- Timestamp outside acceptable freshness window triggers replay-attack rejection
- Payload evidence mismatch indicates tampering or corruption
- Empty or schema-invalid request body returns an error
- Unrecognized signature algorithm may result in undetermined status

## How this service works

Validate declared signature status, freshness and payload evidence

## Output

Returns a structured assessment of the webhook's declared signature status (valid/invalid), freshness evaluation (to detect stale or replayed payloads), and payload evidence integrity — yielding an overall trust verdict indicating whether the webhook is safe to act upon.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema"
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/webhook-verifier-19174f75/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from phion.systems](https://www.zero.xyz/host/phion.systems/llms.txt)