{ "openapi": "3.1.0", "info": { "title": "TxGuard", "version": "0.1.0", "summary": "Deterministic Base transaction and x402 payment preflight for agents, paid per call.", "description": "TxGuard tells an agent what a Base transaction actually does before it signs one. It decodes calldata against verified ABIs, resolves every known proxy pattern including the legacy slot Base USDC really uses, unwraps multicall wrappers recursively, classifies allowances against the token's own supply rather than a list of sentinel values, and runs the full x402 authorization check table against the quote a payment claims to satisfy. There is no model anywhere in it. When a four-byte selector matches more than one signature it returns unknown and hands back every candidate, because a confident decode of an ambiguous selector is how a preflight API becomes dangerous.", "contact": { "email": "support@schemasure.com" }, "x-policy-version": "2026-08-03" }, "servers": [ { "url": "https://txguard.schemasure.com" } ], "paths": { "/v1/tx/preflight": { "post": { "operationId": "txguard_v1_tx_preflight", "summary": "Explain and check a Base transaction or x402 payment authorization before signing it", "description": "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.", "x-payment-info": { "x402Version": 2, "scheme": "exact", "network": "eip155:8453", "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", "amountAtomic": "10000", "priceUsd": 0.01, "payTo": "0x9876af0F6D8Ed5155Cd02d1ca56D128601612690", "policy": "charge only on a successful, usable result" }, "requestBody": { "required": true, "content": { "application/json": { "schema": { "$schema": "https://json-schema.org/draft/2020-12/schema", "title": "TxPreflightRequest", "type": "object", "additionalProperties": false, "description": "Send exactly one of unsigned_tx, tx_hash, typed_data, or authorization.", "oneOf": [ { "required": [ "unsigned_tx" ] }, { "required": [ "tx_hash" ] }, { "required": [ "typed_data" ] }, { "required": [ "authorization" ] } ], "properties": { "unsigned_tx": { "type": "object", "additionalProperties": false, "description": "A transaction you are about to sign. `to: null` is a deployment.", "properties": { "from": { "type": "string", "pattern": "^0x[0-9a-fA-F]{40}$" }, "to": { "type": [ "string", "null" ] }, "value": { "type": "string", "description": "Wei." }, "data": { "type": "string", "pattern": "^0x[0-9a-fA-F]*$" } } }, "tx_hash": { "type": "string", "pattern": "^0x[0-9a-fA-F]{64}$", "description": "An existing Base transaction to explain." }, "typed_data": { "type": "object", "required": [ "domain", "primaryType", "message" ], "description": "EIP-712 payload. TransferWithAuthorization and ReceiveWithAuthorization get the x402 check table; any other primaryType is reported unrecognised, not analysed.", "properties": { "domain": { "type": "object" }, "types": { "type": "object" }, "primaryType": { "type": "string" }, "message": { "type": "object" } } }, "authorization": { "type": "object", "additionalProperties": false, "required": [ "from", "to", "value", "validAfter", "validBefore", "nonce" ], "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": { "from": { "type": "string", "pattern": "^0x[0-9a-fA-F]{40}$" }, "to": { "type": "string", "pattern": "^0x[0-9a-fA-F]{40}$" }, "value": { "type": "string" }, "validAfter": { "type": "string" }, "validBefore": { "type": "string" }, "nonce": { "type": "string", "pattern": "^0x[0-9a-fA-F]*$" }, "signature": { "type": "string", "pattern": "^0x[0-9a-fA-F]*$" }, "kind": { "type": "string", "enum": [ "transfer", "receive" ] }, "asset": { "type": "string", "pattern": "^0x[0-9a-fA-F]{40}$" } } }, "expected_quote": { "type": "object", "description": "The x402 quote this payment claims to satisfy. Enables the comparison checks.", "additionalProperties": false, "properties": { "scheme": { "type": "string" }, "network": { "type": "string" }, "amount": { "type": "string" }, "asset": { "type": "string" }, "payTo": { "type": "string" }, "maxTimeoutSeconds": { "type": "number" }, "extra": { "type": "object" } } }, "simulate": { "type": "boolean", "default": false, "description": "Run eth_simulateV1 with asset tracing. Priced at $0.015 instead of $0.01, and targets P50 2s / P95 5s rather than the static path's 500ms / 2s." } } }, "example": { "unsigned_tx": { "from": "0x9F2C5E4A8db1C3a7E6B0d4f8C1E2a5b7D9C0e3F4", "to": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", "value": "0", "data": "0xa9059cbb0000000000000000000000005d3e1a9b7c2f4e8a0b6d3c5f9e1a7b4d2c8f0a6e0000000000000000000000000000000000000000000000000000000000002710" }, "expected_quote": { "scheme": "exact", "network": "eip155:8453", "amount": "10000", "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", "payTo": "0x1a2B3c4D5E6F7a8B9c0D1e2F3A4b5C6d7E8F9a0b", "maxTimeoutSeconds": 60, "extra": { "name": "USD Coin", "version": "2" } } } } } }, "responses": { "200": { "description": "Successful result envelope", "content": { "application/json": { "schema": { "$schema": "https://json-schema.org/draft/2020-12/schema", "title": "TxPreflightEnvelope", "type": "object", "required": [ "ok", "verdict", "confidence", "risk_codes", "evidence", "result", "policy_version", "request_hash", "data_versions", "warnings" ], "properties": { "ok": { "type": "boolean" }, "verdict": { "type": "string", "enum": [ "allow", "warn", "block", "unknown" ], "description": "Precedence: block, then unknown, then warn, then allow." }, "confidence": { "type": "number", "minimum": 0, "maximum": 1 }, "risk_codes": { "type": "array", "items": { "type": "string" } }, "evidence": { "type": "array", "items": { "type": "object" } }, "policy_version": { "type": "string" }, "request_hash": { "type": "string", "pattern": "^sha256:[0-9a-f]{64}$" }, "warnings": { "type": "array", "items": { "type": "string" } }, "data_versions": { "type": "object", "required": [ "denylist", "abi_packs", "signature_index", "policy", "chain" ] }, "result": { "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" ], "properties": { "intent": { "type": "object", "required": [ "kind", "summary", "decode_source", "calls", "truncated" ], "properties": { "decode_source": { "type": "string", "enum": [ "verified-abi", "bundled-abi", "offline-index", "live-lookup", "unresolved" ] } } }, "approvals": { "type": "array", "items": { "type": "object", "properties": { "scope": { "type": "string", "enum": [ "infinite", "effectively_infinite", "bounded" ] } } } }, "proxy": { "type": "object", "properties": { "kind": { "type": "string", "enum": [ "none", "eip1167", "eip1967", "eip1967-beacon", "eip1822", "zeppelinos", "diamond", "unknown" ] } } } } } } }, "example": { "ok": true, "verdict": "block", "confidence": 1, "risk_codes": [ "RECIPIENT_MISMATCH", "RPC_UNAVAILABLE" ], "evidence": [ { "code": "RECIPIENT_MISMATCH", "severity": "critical", "detail": "Pays 0x5D3e1a9b7c2f4E8A0b6d3c5F9E1A7b4D2C8f0a6E, but the quote names 0x1a2B3c4D5E6F7a8B9c0D1e2F3A4b5C6d7E8F9a0b. Signing this pays someone other than the party you are buying from.", "source": "quote-comparison", "data": { "field": "payTo", "expected": "0x1a2B3c4D5E6F7a8B9c0D1e2F3A4b5C6d7E8F9a0b", "actual": "0x5D3e1a9b7c2f4E8A0b6d3c5F9E1A7b4D2C8f0a6E" } }, { "code": "RPC_UNAVAILABLE", "severity": "medium", "detail": "No Base RPC endpoint is configured, so chain-dependent fields are unknown rather than assumed. See result.unresolved.", "source": "rpc" } ], "result": { "input_shape": "unsigned_tx", "chain": "eip155:8453", "intent": { "kind": "erc20_transfer", "summary": "Transfer 10000 base units of token 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913 to 0x5D3e1a9b7c2f4E8A0b6d3c5F9E1A7b4D2C8f0a6E.", "decode_source": "bundled-abi", "selector": "0xa9059cbb", "signature": "transfer(address,uint256)", "function_name": "transfer", "standard": "erc20", "target": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", "value_wei": "0", "args": [ { "name": "to", "type": "address", "value": "0x5D3e1a9b7c2f4E8A0b6d3c5F9E1A7b4D2C8f0a6E" }, { "name": "amount", "type": "uint256", "value": "10000" } ], "calls": [], "depth": 0, "truncated": false }, "expected_transfers": [ { "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", "asset_kind": "erc20", "from": "0x9f2C5E4a8DB1C3A7e6b0d4f8C1e2A5b7d9c0E3f4", "to": "0x5D3e1a9b7c2f4E8A0b6d3c5F9E1A7b4D2C8f0a6E", "amount": "10000", "token_id": null, "source": "decode" } ], "approvals": [], "permit_scope": null, "spender": { "address": null, "is_contract": null, "detail": "this transaction grants no allowance, so it has no spender" }, "proxy": { "address": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", "kind": "unknown", "implementation": null, "admin": null, "beacon": null, "upgradeable": null, "slots_probed": [], "detail": "no RPC endpoint is configured, so no slot could be read" }, "authorization_checks": [], "quote_comparison": { "present": true, "matches": false, "fields": [ { "field": "payTo", "expected": "0x1a2B3c4D5E6F7a8B9c0D1e2F3A4b5C6d7E8F9a0b", "actual": "0x5D3e1a9b7c2f4E8A0b6d3c5F9E1A7b4D2C8f0a6E", "matches": false }, { "field": "amount", "expected": "10000", "actual": "10000", "matches": true }, { "field": "asset", "expected": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", "actual": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", "matches": true }, { "field": "chainId", "expected": "8453", "actual": null, "matches": null }, { "field": "extra.name", "expected": "USD Coin", "actual": null, "matches": null }, { "field": "extra.version", "expected": "2", "actual": null, "matches": null } ], "detail": "2 of 3 comparable fields match" }, "simulation": { "requested": false, "status": "not_requested", "asset_changes": [], "gas_used": null, "block_number": null, "detail": "simulation was not requested; send simulate: true to run one" }, "candidate_signatures": [], "denylist_hits": [], "unresolved": [ "proxy status of 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913 is unknown: no RPC endpoint is configured, so no slot could be read" ], "rpc": { "configured": false, "reachable": null, "endpoints": [] } }, "policy_version": "2026-08-03", "request_hash": "sha256:6d5c717eb5eede165dada2645ad0944430ff492739cf58d0c2dad2b812f0ddb4", "data_versions": { "denylist": "2026-08-03.1", "abi_packs": "2026-08-03.1", "signature_index": "2026-08-03.1", "policy": "2026-08-03", "chain": "eip155:8453" }, "warnings": [] } } } }, "400": { "description": "INPUT_INVALID", "content": { "application/json": { "schema": { "type": "object", "required": [ "error" ], "additionalProperties": false, "properties": { "error": { "type": "object", "required": [ "code", "message" ], "properties": { "code": { "type": "string" }, "message": { "type": "string" }, "details": {} } } } } } } }, "402": { "description": "Payment required. Body carries the x402 challenge; see PAYMENT-REQUIRED header.", "content": { "application/json": { "schema": { "type": "object", "required": [ "error" ], "additionalProperties": false, "properties": { "error": { "type": "object", "required": [ "code", "message" ], "properties": { "code": { "type": "string" }, "message": { "type": "string" }, "details": {} } } } } } } }, "422": { "description": "UNSUPPORTED or INDETERMINATE. Not charged.", "content": { "application/json": { "schema": { "type": "object", "required": [ "error" ], "additionalProperties": false, "properties": { "error": { "type": "object", "required": [ "code", "message" ], "properties": { "code": { "type": "string" }, "message": { "type": "string" }, "details": {} } } } } } } }, "429": { "description": "RATE_LIMITED", "content": { "application/json": { "schema": { "type": "object", "required": [ "error" ], "additionalProperties": false, "properties": { "error": { "type": "object", "required": [ "code", "message" ], "properties": { "code": { "type": "string" }, "message": { "type": "string" }, "details": {} } } } } } } }, "502": { "description": "Upstream or facilitator unavailable", "content": { "application/json": { "schema": { "type": "object", "required": [ "error" ], "additionalProperties": false, "properties": { "error": { "type": "object", "required": [ "code", "message" ], "properties": { "code": { "type": "string" }, "message": { "type": "string" }, "details": {} } } } } } } }, "504": { "description": "UPSTREAM_TIMEOUT", "content": { "application/json": { "schema": { "type": "object", "required": [ "error" ], "additionalProperties": false, "properties": { "error": { "type": "object", "required": [ "code", "message" ], "properties": { "code": { "type": "string" }, "message": { "type": "string" }, "details": {} } } } } } } } } } } }, "components": { "schemas": { "Error": { "type": "object", "required": [ "error" ], "additionalProperties": false, "properties": { "error": { "type": "object", "required": [ "code", "message" ], "properties": { "code": { "type": "string" }, "message": { "type": "string" }, "details": {} } } } } } } }