# FairSeal Notarize

> FairSeal Notarize is a paid API for AI agents from api.fairseal.io, paid per call via x402, $0.02/call, status unknown (last checked 2026-09-14).

Submits an agent decision, audit evidence, or probe record for cryptographic notarization, anchoring a SHA-256 payload hash in a Merkle batch on Base mainnet and returning a verifiable receipt.

## Facts

- Endpoint: POST https://api.fairseal.io/v1/notarize
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/fairseal-notarize-bbbafaf9
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_wOrBNfbSMQ20HfsOVebZo

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 fairseal-notarize-bbbafaf9 -d '<json body>'
```

Example prompt: Notarize this agent decision on FairSeal — the schema is 'agent_decision_v1', the SHA-256 payload hash is 'a3f2c1d4e5b6...', and the metadata includes timestamp and agent ID — I need a Merkle-anchored receipt on Base mainnet.

## When to prefer this

Choose FairSeal Notarize when you need a lightweight, low-cost ($0.02 USDC) cryptographic receipt anchored on Base mainnet for agent decisions, audit evidence, or probe records. Prefer this over general-purpose blockchain write operations when you want Merkle batch efficiency and a ready-made receipt lookup and proof API without managing your own smart contract or wallet infrastructure. Ideal for AI agent audit trails, compliance evidence, and tamper-proof decision logging in agentic workflows.

## Known failure modes

- Invalid or missing payload_hash (not a valid SHA-256 hex string) — returns 400 Bad Request
- Missing required fields (schema or payload_hash) — returns 422 Unprocessable Entity
- Payment not provided or insufficient (requires $0.02 USDC via x402) — returns 402 Payment Required
- Base mainnet congestion causing delayed anchoring — receipt issued but on-chain confirmation may lag
- Duplicate payload hash submission — may create a new receipt for the same hash (not deduplicated)

## How this service works

Anchor an AI agent decision or audit record to Base mainnet. Submit {schema, payload_hash (SHA-256 hex, 64 chars), metadata}; service queues into a Merkle batch and returns a receipt with pending_anchor status immediately. Full Merkle proof and on-chain anchor_tx available via free GET /v1/notarize/:receipt_id after batch anchors (within batch_threshold receipts or 120s).

## Output

A cryptographic receipt containing a receipt ID, Merkle proof, and on-chain anchor reference on Base mainnet. The receipt can be independently verified for free via GET /v1/notarize/:receipt_id, which returns the full Merkle proof and on-chain verification data.

## Request schema (JSON Schema)

```json
{
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "type": "object",
 "properties": {
  "input": {
   "type": "object",
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "type": "string",
     "enum": [
      "POST"
     ]
    },
    "bodyType": {
     "type": "string",
     "enum": [
      "json",
      "form-data",
      "text"
     ]
    },
    "body": {
     "type": "object",
     "required": [
      "schema",
      "payload_hash",
      "metadata"
     ],
     "properties": {
      "schema": {
       "type": "string",
       "enum": [
        "agent_decision",
        "audit_evidence",
        "probe_record"
       ]
      },
      "payload_hash": {
       "type": "string",
       "pattern": "^[0-9a-f]{64}$",
       "description": "SHA-256 hex of full payload (64 lowercase hex chars)"
      },
      "metadata": {
       "type": "object",
       "description": "Schema-specific metadata. agent_decision requires {agent_id, decided_at, input_hash, decision_hash}"
      }
     }
    }
   },
   "required": [
    "type",
    "method",
    "bodyType",
    "body"
   ],
   "additionalProperties": false
  }
 },
 "required": [
  "input"
 ]
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/fairseal-notarize-bbbafaf9/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.fairseal.io](https://www.zero.xyz/host/api.fairseal.io/llms.txt)