402Signal checks the endpoint, price and recipient before your agent pays, on x402 and MPP

[
  {
    "scheme": "exact",
    "network": "eip155:8453",
    "payTo": "0xa2604ae688228af8349363770351bfcec66d4fa0",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "amount": "3000",
    "maxTimeoutSeconds": 60
  },
  {
    "scheme": "exact",
    "network": "solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp",
    "payTo": "C8qDYG8NTyvdY85gvGfs1WajwGhiLu6f1vi3JaG1r1iA",
    "asset": "EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v",
    "amount": "3000",
    "maxTimeoutSeconds": 60
  },
  {
    "scheme": "exact",
    "network": "algorand:wGHE2Pwdvd7S12BL5FaOP20EGYesN73ktiC1qzkkit8=",
    "payTo": "N2JSJZCSORMYGYO2NSIYRUEMBFRHEOMYODVXV2MXYYHB5H2JVUGG6NJ4NQ",
    "asset": "31566704",
    "amount": "3000",
    "maxTimeoutSeconds": 60
  }
]

{
  "bazaar": {
    "info": {
      "input": {
        "body": {
          "need": "erc20 token balance",
          "url": "https://example.com/x402/balance"
        },
        "bodyType": "json",
        "method": "POST",
        "type": "http"
      },
      "output": {
        "example": {
          "billing": {
            "amount_atomic": "3000",
            "asset": "USDC",
            "condition": "live_eligible_route_found",
            "display_amount": "$0.003",
            "model": "success_only_v1",
            "rail": "base",
            "settled": true,
            "settlement_attempted": true,
            "settlement_state": "settled"
          },
          "has_402_challenge": true,
          "health": {
            "has_402_challenge": true,
            "last_probe": "2026-08-29T22:00:00-04:00",
            "latency_ms": 87,
            "live": true,
            "status": 402
          },
          "latency_ms": 87,
          "live": true,
          "probed_at": "2026-08-29T22:00:00-04:00",
          "status": 402,
          "url": "https://example.com/x402/balance"
        },
        "type": "json"
      }
    },
    "schema": {
      "$schema": "https://json-schema.org/draft/2020-12/schema",
      "properties": {
        "input": {
          "additionalProperties": false,
          "properties": {
            "body": {
              "anyOf": [
                {
                  "required": [
                    "need"
                  ]
                },
                {
                  "required": [
                    "url"
                  ]
                }
              ],
              "properties": {
                "need": {
                  "type": "string"
                },
                "require_route_binding": {
                  "description": "Opt in to a signed v4 route binding; implies require_transparency even if false. Default false; ordinary requests keep v3. A ranked winner that cannot bind may fall through to the next already-probed selectable bindable candidate; 503 route_binding_unavailable only when none remain. wrapExactAuthorize reports state=binding_unavailable with keep_calling_route true; policy working, not a crash. Buyer verifies raw response JSON with a pinned log key and compares the current seller request and challenge before signing. Expiry or changed terms do not undo a settled checking fee. Guide: https://402signal.com/developers#route-binding",
                  "type": "boolean"
                },
                "require_transparency": {
                  "description": "Require a durable leaf and signed checkpoint receipt on HTTP 200. Default false; require_route_binding=true also requires transparency. Receipt failure after settlement remains billed. Private replay records support bounded recovery of the original response; they are not long-term evidence storage. Keep your own copy outside public logs.",
                  "type": "boolean"
                },
                "url": {
                  "type": "string"
                }
              },
              "type": "object"
            },
            "bodyType": {
              "enum": [
                "json",
                "form-data",
                "text"
              ],
              "type": "string"
            },
            "headers": {
              "additionalProperties": {
                "type": "string"
              },
              "type": "object"
            },
            "method": {
              "enum": [
                "POST",
                "PUT",
                "PATCH"
              ],
              "type": "string"
            },
            "queryParams": {
              "additionalProperties": {
                "type": "string"
              },
              "type": "object"
            },
            "type": {
              "const": "http",
              "type": "string"
            }
          },
          "required": [
            "type",
            "method",
            "bodyType",
            "body"
          ],
          "type": "object"
        },
        "output": {
          "properties": {
            "example": {
              "type": "object"
            },
            "type": {
              "type": "string"
            }
          },
          "required": [
            "type"
          ],
          "type": "object"
        }
      },
      "required": [
        "input"
      ],
      "type": "object"
    }
  }
}

curl "https://402signal.com/route"
# -> 402 Payment Required, accepts[] lists how to pay
# retry with a PAYMENT-SIGNATURE (or PAYMENT header) once paid

const res = await fetch("https://402signal.com/route");
if (res.status === 402) {
  const { accepts } = await res.json();
  // pay one of accepts[] via an x402 client, then retry with the payment header
}

import httpx
res = httpx.get("https://402signal.com/route")
if res.status_code == 402:
    accepts = res.json()["accepts"]
    # pay one of accepts[] via an x402 client, then retry with the payment header