Explain and preflight an unsigned Base transaction, EIP-712 typed data, or an EI
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.
Answeringour last check, 2026-09-24
1 of 1checks answered this week
1029 msmedian answer time
$0.01listed price per call
$0.01price it asked us
Paid test badge: not yet. The checks above are free: we call the tool without paying and read the payment request it sends back. The Verified badge needs paid calls whose answers match the promised output, and nobody can buy a badge.
Endpoint
POST https://txguard.schemasure.com/v1/tx/preflight
| Category | Everything else |
|---|---|
| Provider host | txguard.schemasure.com |
| Networks | eip155:8453 |
| Payment schemes | exact |
| Self-reported calls, 30 days | 36 from 3 payers (the provider's figure, not ours) |
Our checks, last 30 days
| Day | Result | HTTP | Asked | Time |
|---|---|---|---|---|
| 2026-09-24 | valid payment request | 402 | $0.01 | 1029 ms |
Example input (from the provider)
{
"body": {
"expected_quote": {
"amount": "10000",
"asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
"extra": {
"name": "USD Coin",
"version": "2"
},
"maxTimeoutSeconds": 60,
"network": "eip155:8453",
"payTo": "0x1a2B3c4D5E6F7a8B9c0D1e2F3A4b5C6d7E8F9a0b",
"scheme": "exact"
},
"unsigned_tx": {
"data": "0xa9059cbb0000000000000000000000005d3e1a9b7c2f4e8a0b6d3c5f9e1a7b4d2c8f0a6e0000000000000000000000000000000000000000000000000000000000002710",
"from": "0x9F2C5E4A8db1C3a7E6B0d4f8C1E2a5b7D9C0e3F4",
"to": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
"value": "0"
}
},
"bodyType": "json",
"method": "POST",
"type": "http"
}
Promised output schema (from the provider)
{
"$schema": "https://json-schema.org/draft/2020-12/schema",
"properties": {
"input": {
"additionalProperties": false,
"properties": {
"body": {
"$schema": "https://json-schema.org/draft/2020-12/schema",
"additionalProperties": false,
"description": "Send exactly one of unsigned_tx, tx_hash, typed_data, or authorization.",
"oneOf": [
{
"required": [
"unsigned_tx"
]
},
{
"required": [
"tx_hash"
]
},
{
"required": [
"typed_data"
]
},
{
"required": [
"authorization"
]
}
],
"properties": {
"authorization": {
"additionalProperties": false,
"description": "An EIP-3009 authorization, which is what an x402 `exact` payment is. value in base units, validAfter/validBefore in unix seconds, nonce 32 random bytes not a counter.",
"properties": {
"asset": {
"pattern": "^0x[0-9a-fA-F]{40}$",
"type": "string"
},
"from": {
"pattern": "^0x[0-9a-fA-F]{40}$",
"type": "string"
},
"kind": {
"enum": [
"transfer",
"receive"
],
"type": "string"
},
"nonce": {
"pattern": "^0x[0-9a-fA-F]*$",
"type": "string"
},
"signature": {
"pattern": "^0x[0-9a-fA-F]*$",
"type": "string"
},
"to": {
"pattern": "^0x[0-9a-fA-F]{40}$",
"type": "string"
},
"validAfter": {
"type": "string"
},
"validBefore": {
"type": "string"
},
"value": {
"type": "string"
}
},
"required": [
"from",
"to",
"value",
"validAfter",
"validBefore",
"nonce"
],
"type": "object"
},
"expected_quote": {
"additionalProperties": false,
"description": "The x402 quote this payment claims to satisfy. Enables the comparison checks.",
"properties": {
"amount": {
"type": "string"
},
"asset": {
"type": "string"
},
"extra": {
"type": "object"
},
"maxTimeoutSeconds": {
"type": "number"
},
"network": {
"type": "string"
},
"payTo": {
"type": "string"
},
"scheme": {
"type": "string"
}
},
"type": "object"
},
"simulate": {
"default": false,
"description": "Run eth_simulateV1 with asset tracing. Priced at $0.015 instead of $0.01, and targets P50 2s / P95 5s rather than the static path's 500ms / 2s.",
"type": "boolean"
},
"tx_hash": {
"description": "An existing Base transaction to explain.",
"pattern": "^0x[0-9a-fA-F]{64}$",
"type": "string"
},
"typed_data": {
"description": "EIP-712 payload. TransferWithAuthorization and ReceiveWithAuthorization get the x402 check table; any other primaryType is reported unrecognised, not analysed.",
"properties": {
"domain": {
"type": "object"
},
"message": {
"type": "object"
},
"primaryType": {
"type": "string"
},
"types": {
"type": "object"
}
},
"required": [
"domain",
"primaryType",
"message"
],
"type": "object"
},
"unsigned_tx": {
"additionalProperties": false,
"description": "A transaction you are about to sign. `to: null` is a deployment.",
"properties": {
"data": {
"pattern": "^0x[0-9a-fA-F]*$",
"type": "string"
},
"from": {
"pattern": "^0x[0-9a-fA-F]{40}$",
"type": "string"
},
"to": {
"type": [
"string",
"null"
]
},
"value": {
"description": "Wei.",
"type": "string"
}
},
"type": "object"
}
},
"title": "TxPreflightRequest",
"type": "object"
},
"bodyType": {
"enum": [
"json",
"form-data",
"text"
],
"type": "string"
},
"method": {
"enum": [
"POST"
],
"type": "string"
},
"type": {
"const": "http",
"type": "string"
}
},
"required": [
"type",
"method",
"bodyType",
"body"
],
"type": "object"
}