Put one call between “agent decided to buy” and “agent signs the swap”:
import requests
r = requests.get("https://x402-data-api.sigrunner.workers.dev/gate/swap/preview", params={"token": token}).json()
if r.get("decision") != "go":
raise RuntimeError(f"blocked: {r}")
/gate/swap returns go / hold / block ($0.008 per call, x402). The deeper /chain/token-report ($0.01) returns the full evidence. LangChain, CrewAI and Vercel AI SDK examples: greyridge-x402-tools.
The free preview allows 3 real-token checks/day/IP so you can wire it before paying.