TX
Payments · x402 · early usage

Explain and preflight an unsigned Base transaction, EIP-712 typed data, or an EIP-3009…

Explain and preflight an unsigned Base transaction, EIP-712 typed data, or an EIP-3009 x402 payment authorization before you sign it. Decodes intent against verified ABIs, resolves proxies, classifies approvals, and checks a payment authorization against the…

by txguard.schemasure.com · discovered, not yet claimed by its owner · updated 2026-10-12

30d calls37
30d payers6
MethodPOST
Outputjson

Mirrored from Coinbase's public x402 Bazaar. The description is the provider's own text and has not been reviewed here; the payment requirements are copied as published.

What it does

Explain and preflight an unsigned Base transaction, EIP-712 typed data, or an EIP-3009 x402 payment authorization before you sign it. Decodes intent against verified ABIs, resolves proxies, classifies approvals, and checks a payment authorization against the quote it claims to pay: recipient, amount, asset, chain, freshness, and nonce replay. Returns unknown rather than guessing when a selector is ambiguous. Not a guarantee that a transaction is safe or profitable.

Tags: base · transaction · preflight · x402 · eip3009 · bazaar

Call contract

Method
POST
Input
json
Output
json
Last paid call
2026-10-12
Input example from Bazaar metadata
{
  "expected_quote": {
    "amount": "10000",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "extra": {
      "name": "USD Coin",
      "version": "2"
    },
    "maxTimeoutSeconds": 60,
    "network": "eip155:8453",
    "payTo": "0x1a2B3c4D5E6F7a8B9c0D1e2F3A4b5C6d7E8F9a0b",
    "scheme": "exact"
  },
  "unsigned_tx": {
    "data": "0xa9059cbb0000000000000000000000005d3e1a9b7c2f4e8a0b6d3c5f9e1a7b4d2c8f0a6e0000000000000000000000000000000000000000000000000000000000002710",
    "from": "0x9F2C5E4A8db1C3a7E6B0d4f8C1E2a5b7D9C0e3F4",
    "to": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "value": "0"
  }
}
Output example
{
  "confidence": 1,
  "data_versions": {
    "abi_packs": "2026-08-03.1",
    "chain": "eip155:8453",
    "denylist": "2026-08-03.1",
    "policy": "2026-08-03",
    "signature_index": "2026-08-03.1"
  },
  "evidence": [
    {
      "code": "RECIPIENT_MISMATCH",
      "data": {
        "actual": "0x5D3e1a9b7c2f4E8A0b6d3c5F9E1A7b4D2C8f0a6E",
        "expected": "0x1a2B3c4D5E6F7a8B9c0D1e2F3A4b5C6d7E8F9a0b",
        "field": "payTo"
      },
      "detail": "Pays 0x5D3e1a9b7c2f4E8A0b6d3c5F9E1A7b4D2C8f0a6E, but the quote names 0x1a2B3c4D5E6F7a8B9c0D1e2F3A4b5C6d7E8F9a0b. Signing this pays someone other than the party you are buying from.",
      "severity": "critical",
      "source": "quote-comparison"
    },
    {
      "code": "RPC_UNAVAILABLE",
      "detail": "No Base RPC endpoint is configured, so chain-dependent fields are unknown rather than assumed. See result.unresolved.",
      "severity": "medium",
      "source": "rpc"
    }
  ],
  "ok": true,
  "policy_version": "2026-08-03",
  "request_hash": "sha256:6d5c717eb5eede165dada2645ad0944430ff492739cf58d0c2dad2b812f0ddb4",
  "result": {
    "approvals": [],
    "authorization_checks": [],
    "candidate_signatures": [],
    "chain": "eip155:8453",
    "denylist_hits": [],
    "expected_transfers": [
      {
        "amount": "10000",
        "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
        "asset_kind": "erc20",
        "from": "0x9f2C5E4a8DB1C3A7e6b0d4f8C1e2A5b7d9c0E3f4",
        "source": "decode",
        "to": "0x5D3e1a9b7c2f4E8A0b6d3c5F9E1A7b4D2C8f0a6E",
        "token_id": null
      }
    ],
    "input_shape": "unsigned_tx",
    "intent": {
      "args": [
        {
          "name": "to",
          "type": "address",
          "value": "0x5D3e1a9b7c2f4E8A0b6d3c5F9E1A7b4D2C8f0a6E"
        },
        {
          "name": "amount",
          "type": "uint256",
          "value": "10000"
        }
      ],
      "calls": [],
      "decode_source": "bundled-abi",
      "depth": 0,
      "function_name": "transfer",
      "kind": "erc20_transfer",
      "selector": "0xa9059cbb",
      "signature": "transfer(address,uint256)",
      "standard": "erc20",
      "summary": "Transfer 10000 base units of token 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913 to 0x5D3e1a9b7c2f4E8A0b6d3c5F9E1A7b4D2C8f0a6E.",
      "target": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
      "truncated": false,
      "value_wei": "0"
    },
    "permit_scope": null,
    "proxy": {
      "address": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
      "admin": null,
      "beacon": null,
      "detail": "no RPC endpoint is configured, so no slot could be read",
      "implementation": null,
      "kind": "unknown",
      "slots_probed": [],
      "upgradeable": null
    },
    "quote_comparison": {
      "detail": "2 of 3 comparable fields match",
      "fields": [
        {
          "actual": "0x5D3e1a9b7c2f4E8A0b6d3c5F9E1A7b4D2C8f0a6E",
          "expected": "0x1a2B3c4D5E6F7a8B9c0D1e2F3A4b5C6d7E8F9a0b",
          "field": "payTo",
          "matches": false
        },
        {
          "actual": "10000",
          "expected": "10000",
          "field": "amount",
          "matches": true
        },
        {
          "actual": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
          "expected": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
          "field": "asset",
          "matches": true
        },
        {
          "actual": null,
          "expected": "8453",
          "field": "chainId",
          "matches": null
        },
        {
          "actual": null,
          "expected": "USD Coin",
          "field": "extra.name",
          "matches": null
        },
        {
          "actual": null,
          "expected": "2",
          "field": "extra.version",
          "matches": null
        }
      ],
      "matches": false,
      "present": true
    },
    "rpc": {
      "configured": false,
      "endpoints": [],
      "reachable": null
    },
    "simulation": {
      "asset_changes": [],
      "block_number": null,
      "detail": "simulation was not requested; send simulate: true to run one",
      "gas_used": null,
      "requested": false,
      "status": "not_requested"
    },
    "spender": {
      "address": null,
      "detail": "this transaction grants no allowance, so it has no spender",
      "is_contract": null
    },
    "unresolved": [
      "proxy status of 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913 is unknown: no RPC endpoint is configured, so no slot could be read"
    ]
  },
  "risk_codes": [
    "RECIPIENT_MISMATCH",
    "RPC_UNAVAILABLE"
  ],
  "verdict": "block",
  "warnings": []
}

Use with an agent

  1. Discover. Agents find this listing with GET https://bazaar.saylorinnovations.com/discovery/search?query=…, the MCP tool search_resources, or /discovery/resources.
  2. Inspect. Fetch /resources/26948.json for the price and payment options.
  3. Pay. Call GET https://txguard.schemasure.com/v1/tx/preflight. The provider answers 402 with its payment requirements. An x402 client signs one of the options below and retries with PAYMENT-SIGNATURE.
  4. Execute. The provider returns 200 with the data. Agent Bazaar is not in the request path and never sees your payment.

For humans

You don't need an account or an API key; you need a wallet holding a small amount of USDC on Base, and an x402-capable client (see the examples below). Call the endpoint unpaid first to see exactly what it asks for.

Pricing & payment

Price
$0.02 / request
Protocol
x402 v2
Auth
No account or API key. Pay per request.
Networks
Base
Demand
37 calls · 6 unique payers in 30d (public x402 Bazaar data)

x402 payment requirements

SchemeNetworkAssetAmountPay toTimeout
exactBase
eip155:8453
USDC$0.020x9876af0F6D8Ed5155Cd02d1ca56D12860161269060s
accepts[] (raw JSON)
[
  {
    "scheme": "exact",
    "network": "eip155:8453",
    "payTo": "0x9876af0F6D8Ed5155Cd02d1ca56D128601612690",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "amount": "20000",
    "amountUsd": 0.02,
    "maxTimeoutSeconds": 60
  }
]

Schemas

Output schema (JSON Schema)
{
  "properties": {
    "example": {
      "$schema": "https://json-schema.org/draft/2020-12/schema",
      "properties": {
        "confidence": {
          "maximum": 1,
          "minimum": 0,
          "type": "number"
        },
        "data_versions": {
          "required": [
            "denylist",
            "abi_packs",
            "signature_index",
            "policy",
            "chain"
          ],
          "type": "object"
        },
        "evidence": {
          "items": {
            "type": "object"
          },
          "type": "array"
        },
        "ok": {
          "type": "boolean"
        },
        "policy_version": {
          "type": "string"
        },
        "request_hash": {
          "pattern": "^sha256:[0-9a-f]{64}$",
          "type": "string"
        },
        "result": {
          "properties": {
            "approvals": {
              "items": {
                "properties": {
                  "scope": {
                    "enum": [
                      "infinite",
                      "effectively_infinite",
                      "bounded"
                    ],
                    "type": "string"
                  }
                },
                "type": "object"
              },
              "type": "array"
            },
            "intent": {
              "properties": {
                "decode_source": {
                  "enum": [
                    "verified-abi",
                    "bundled-abi",
                    "offline-index",
                    "live-lookup",
                    "unresolved"
                  ],
                  "type": "string"
                }
              },
              "required": [
                "kind",
                "summary",
                "decode_source",
                "calls",
                "truncated"
              ],
              "type": "object"
            },
            "proxy": {
              "properties": {
                "kind": {
                  "enum": [
                    "none",
                    "eip1167",
                    "eip1967",
                    "eip1967-beacon",
                    "eip1822",
                    "zeppelinos",
                    "diamond",
                    "unknown"
                  ],
                  "type": "string"
                }
              },
              "type": "object"
            }
          },
          "required": [
            "input_shape",
            "chain",
            "intent",
            "expected_transfers",
            "approvals",
            "permit_scope",
            "spender",
            "proxy",
            "authorization_checks",
            "quote_comparison",
            "simulation",
            "candidate_signatures",
            "denylist_hits",
            "unresolved",
            "rpc"
          ],
          "type": "object"
        },
        "risk_codes": {
          "items": {
            "type": "string"
          },
          "type": "array"
        },
        "verdict": {
          "description": "Precedence: block, then unknown, then warn, then allow.",
          "enum": [
            "allow",
            "warn",
            "block",
            "unknown"
          ],
          "type": "string"
        },
        "warnings": {
          "items": {
            "type": "string"
          },
          "type": "array"
        }
      },
      "required": [
        "ok",
        "verdict",
        "confidence",
        "risk_codes",
        "evidence",
        "result",
        "policy_version",
        "request_hash",
        "data_versions",
        "warnings"
      ],
      "title": "TxPreflightEnvelope",
      "type": "object"
    },
    "type": {
      "type": "string"
    }
  },
  "required": [
    "type"
  ],
  "type": "object"
}
Example shape — generated from the schema, not a captured live response
{
  "example": {
    "confidence": 0,
    "data_versions": {},
    "evidence": [
      {}
    ],
    "ok": true,
    "policy_version": "string",
    "request_hash": "string",
    "result": {
      "approvals": [
        {
          "scope": "infinite"
        }
      ],
      "intent": {
        "decode_source": "verified-abi"
      },
      "proxy": {
        "kind": "none"
      }
    },
    "risk_codes": [
      "string"
    ],
    "verdict": "allow",
    "warnings": [
      "string"
    ]
  },
  "type": "string"
}

Examples

curl
curl "https://txguard.schemasure.com/v1/tx/preflight"
# -> 402 Payment Required, accepts[] lists how to pay
# retry with a PAYMENT-SIGNATURE (or PAYMENT header) once paid
JavaScript
const res = await fetch("https://txguard.schemasure.com/v1/tx/preflight");
if (res.status === 402) {
  const { accepts } = await res.json();
  // pay one of accepts[] via an x402 client, then retry with the payment header
}
Python
import httpx
res = httpx.get("https://txguard.schemasure.com/v1/tx/preflight")
if res.status_code == 402:
    accepts = res.json()["accepts"]
    # pay one of accepts[] via an x402 client, then retry with the payment header

Details

Provider
txguard.schemasure.com
Endpoint
https://txguard.schemasure.com/v1/tx/preflight
Machine-readable
/resources/26948.json