# Ghost Identity — API Schema Fingerprint Checker

> Ghost Identity — API Schema Fingerprint Checker is a paid API for AI agents from ghost-identity.ghost-agent-os.workers.dev, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-14).

Checks a public JSON Schema or OpenAPI document URL for changes by comparing its current fingerprint against a previously known one

## Facts

- Endpoint: POST https://ghost-identity.ghost-agent-os.workers.dev/v1/check
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/ghost-identity-api-schema-fingerprint-checker-7b537d0f
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_LrxFTfqNentjIx1YYiamg

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 ghost-identity-api-schema-fingerprint-checker-7b537d0f -d '<json body>'
```

Example prompt: Check whether the OpenAPI spec at https://api.example.com/openapi.json has changed since the last time I looked — here's the fingerprint from my previous check: abc123def456.

## When to prefer this

Use this endpoint when you need to detect whether a remote JSON Schema or OpenAPI document has changed, either for the first time (establishing a baseline) or by comparing against a stored fingerprint. Ideal for agents that depend on third-party APIs and need to monitor for breaking schema changes without storing full document copies. Choose this over generic HTTP polling when you want a semantic fingerprint comparison with payment handled automatically via x402.

## Known failure modes

- URL is unreachable or returns a non-200 response — schema cannot be fetched
- URL does not point to a valid JSON Schema or OpenAPI document — parsing fails
- Payment via x402 fails or wallet lacks sufficient USDC — call is rejected with 402
- Schema document exceeds size limits — fingerprinting may time out or error
- known_fingerprint value is malformed or too long (>128 chars) — validation error

## How this service works

Paid per call via x402 (exact / eip155:8453 / USDC). Any x402-capable client pays automatically: agentcash, @x402/fetch, x402-fetch. Every paid operation carries x-payment-info; the same terms are served live as a 402.

## Output

Returns the current fingerprint of the schema document at the provided URL, and whether it differs from the supplied known fingerprint. Allows agents to detect schema changes, track API evolution, or establish a baseline fingerprint for first-time observations.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "url": {
   "type": "string",
   "title": "Url",
   "maxLength": 2048,
   "description": "Public URL of a JSON Schema or OpenAPI document"
  },
  "known_fingerprint": {
   "type": "string",
   "title": "Known Fingerprint",
   "default": "",
   "maxLength": 128,
   "description": "The fingerprint from a previous check. Empty means first observation."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/ghost-identity-api-schema-fingerprint-checker-7b537d0f/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from ghost-identity.ghost-agent-os.workers.dev](https://www.zero.xyz/host/ghost-identity.ghost-agent-os.workers.dev/llms.txt)