# SignGate x402 Agent Buyer Identity Preflight

> SignGate x402 Agent Buyer Identity Preflight is a paid API for AI agents from base-agent-preflight.bytoken2023.workers.dev, paid per call via x402, $0.1/call, status unknown (last checked 2026-09-14).

Validates whether an AI agent is authorized to make a specific x402 micropayment purchase by checking buyer identity, product category, price thresholds, and approval policy before the transaction occurs.

## Facts

- Endpoint: GET https://base-agent-preflight.bytoken2023.workers.dev/v1/x402/agent/rpc-payment-guard
- Price: $0.1/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/signgate-x402-agent-buyer-identity-preflight-9a8a9395
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_7xsf1wQEyDmDkUcvAd8ir

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 signgate-x402-agent-buyer-identity-preflight-9a8a9395
```

Example prompt: Before you pay for that x402 RPC endpoint at https://api.example.com/rpc using 0.05 USDC on eip155:8453, run a preflight check with request ID req-abc123 to make sure this purchase is authorized, the method is eth_call, and my session budget of 5.00 USDC and single-purchase cap of 0.10 USDC aren't exceeded.

## When to prefer this

Use this endpoint when an AI agent needs a governance checkpoint before executing an x402 micropayment — especially when enforcing per-transaction spending caps, session budgets, buyer role policies, or product-category sensitivity rules on Base or other EVM chains. Prefer this over ad-hoc budget checks when you need a structured risk score and audit trail for agent purchases rather than simple balance comparisons.

## Known failure modes

- Invalid or missing required query parameters (request_id, endpoint_url, chain, method, amount_usdc) return a 400 error
- amount_usdc exceeding max_single_usdc triggers a policy flag or rejection
- Session budget exhausted results in a high risk_score or authorization denial
- Malformed chain identifier not matching CAIP-2 pattern returns validation error
- Unknown or unsupported endpoint_url domain may result in high risk flags
- Caller must itself pay $0.1 USDC per call via x402, so an unpaid request returns HTTP 402

## How this service works

Machine-payable service intelligence for discovering, verifying, and monitoring identity, risk, authorization, execution-preflight, and evidence APIs before autonomous agents spend.

## Output

Returns a JSON object containing a risk assessment with a risk_level (e.g. 'low', 'medium', 'high'), a numeric risk_score, any policy flags triggered, along with network info, product identification, identity context, and provenance metadata. A clean response with empty flags and risk_level 'low' signals the agent is authorized to proceed with the purchase.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "request_id",
      "endpoint_url",
      "chain",
      "method",
      "amount_usdc"
     ],
     "properties": {
      "chain": {
       "type": "string",
       "pattern": "^[A-Za-z0-9:_ -]{2,80}$",
       "description": "Requested chain or CAIP-2 network label."
      },
      "method": {
       "type": "string",
       "pattern": "^[A-Za-z0-9_.:-]{2,80}$",
       "description": "RPC method, REST operation, or query action."
      },
      "pay_to": {
       "type": "string",
       "pattern": "^0x[a-fA-F0-9]{40}$",
       "description": "Payment recipient address."
      },
      "request_id": {
       "type": "string",
       "pattern": "^[A-Za-z0-9._:-]{1,128}$",
       "description": "Caller-defined idempotency key for this RPC purchase."
      },
      "amount_usdc": {
       "type": "string",
       "pattern": "^[0-9]+(?:\\.[0-9]{1,6})?$",
       "description": "Requested stablecoin payment amount."
      },
      "endpoint_url": {
       "type": "string",
       "pattern": "^https?://",
       "maxLength": 2048,
       "description": "RPC, x402, REST, or indexed chain-data endpoint URL."
      },
      "max_single_usdc": {
       "type": "string",
       "pattern": "^[0-9]+(?:\\.[0-9]{1,6})?$",
       "description": "Maximum allowed amount for one RPC/data purchase."
      },
      "session_budget_usdc": {
       "type": "string",
       "pattern": "^[0-9]+(?:\\.[0-9]{1,6})?$",
       "description": "Remaining budget for this agent session."
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "network": {
       "type": "string"
      },
      "product": {
       "type": "string"
      },
      "activity": {
       "type": "object"
      },
      "identity": {
       "type": "object"
      },
      "assessment": {
       "type": "object"
      },
      "provenance": {
       "type": "object"
      }
    
… (truncated)
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "network": "eip155:8453",
  "product": "x402-rpc-payment-guard",
  "assessment": {
   "flags": [],
   "risk_level": "low",
   "risk_score": 0
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/signgate-x402-agent-buyer-identity-preflight-9a8a9395/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from base-agent-preflight.bytoken2023.workers.dev](https://www.zero.xyz/host/base-agent-preflight.bytoken2023.workers.dev/llms.txt)