# Referrer Policy Check

> Referrer Policy Check is a paid API for AI agents from api.delx.ai, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-15).

Validates a Referrer-Policy header value against a caller-supplied allowlist and returns a deterministic pass/advisory finding

## Facts

- Endpoint: POST https://api.delx.ai/api/v1/x402/referrer-policy-check
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/referrer-policy-check-f14ab587
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_MRZWxPvuCdTIh-sNchIXx

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 referrer-policy-check-f14ab587 -d '<json body>'
```

Example prompt: Check if the Referrer-Policy value 'no-referrer-when-downgrade' is allowed — the permitted values are 'no-referrer', 'no-referrer-when-downgrade', and 'strict-origin-when-cross-origin'.

## When to prefer this

Use this endpoint when you need a stateless, deterministic, first-party check of a Referrer-Policy header value against a bounded caller-defined allowlist — especially before accepting, caching, redirecting, or retrying a web response. Prefer this over custom code when you want versioned, auditable JSON evidence with an explicit pass/advisory status without relying on an external security provider.

## Known failure modes

- Missing or empty 'value' field returns validation error
- Empty or missing 'allowed' array returns error or automatic advisory
- Value exceeding 8192 characters is rejected
- Allowed array exceeding 256 items is rejected
- Malformed JSON body returns 400-level error
- Payment failure via x402 returns 402 Payment Required

## How this service works

Referrer Policy Check: Referrer Policy Check classifies a Referrer-Policy value against a caller allowlist from bounded caller-supplied values without an external provider. Call Referrer Policy Check before accepting, caching, redirecting, or retrying a caller-supplied web response. Returns normalized web evidence, the computed finding, and an explicit pass or advisory status for Referrer Policy Check as versioned deterministic JSON. Price: $0.001 USDC via x402 on Base. First-party, stateless,…

## Output

Returns a versioned deterministic JSON object containing: the normalized Referrer-Policy evidence extracted from the input, the computed classification finding, and an explicit pass or advisory status indicating whether the value is within the provided allowlist.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "value": {
   "type": "string",
   "maxLength": 8192,
   "description": "Value supplied to Referrer Policy Check; used only for this bounded calculation and processed in memory without retention."
  },
  "allowed": {
   "type": "array",
   "items": {
    "type": "string",
    "maxLength": 8192
   },
   "maxItems": 256,
   "description": "Allowed supplied to Referrer Policy Check; used only for this bounded calculation and processed in memory without retention."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "result": {
   "value": "strict-origin-when-cross-origin",
   "accepted": true
  },
  "schema": "delx/util-referrer-policy-check/v1",
  "status": "pass",
  "evidence": {
   "retained": false,
   "input_sha256": "d9c8b9b264fe994897afb78430721e7bed86899de05bf6d219f03a39c301eaa1",
   "external_calls": 0
  },
  "operation": "web_reliability:referrer_policy_check"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/referrer-policy-check-f14ab587/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.delx.ai](https://www.zero.xyz/host/api.delx.ai/llms.txt)