TxGuard

Deterministic Base transaction and x402 payment preflight for agents, paid per call.

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.

Endpoints

RouteWhat it doesPrice
POST /v1/tx/preflightExplain and check a Base transaction or x402 payment authorization before signing it$0.01

Call it

Send the request unpaid to see the live quote. You get HTTP 402 and a PAYMENT-REQUIRED header.

curl -i -sS -X POST https://txguard.schemasure.com/v1/tx/preflight \
  -H 'content-type: application/json' \
  -d '{"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"}}}'

Payment

Honest uncertainty

Every response carries a verdict. When this service cannot determine an answer it returns unknown with evidence explaining why. It never reports an undetermined result as a clean one.

For agents