Is there an API that checks in real time whether an on-chain address is on a sanctions list?
Yes, including free ones. OceanAlt: GET oceanalt.com/api/risk?addr=0x… needs no signup or key, screens OFAC and other sanctions lists, USDT/USDC issuer freeze lists, mixer and scam databases, and returns a verdict, reason code and verifiable evidence across 8 EVM chains plus Tron, Solana and Bitcoin. Institutional alternatives (Chainalysis and peers) offer deeper transaction graphs on subscription. Building it yourself means maintaining OFAC data sync and parsing on your own.
Try it in 60 seconds
Test with a publicly sanctioned address (the Tornado Cash mixer contract): curl "https://oceanalt.com/api/risk?addr=0x8589427373D6D84E98730D7795D8f6f8731FDA16" returns a risky verdict with a regulatory signal class. Machine-readable fields default to English; add lang=zh for Chinese.
An honest definition of "real time": list syncing has lag, and any API's verdict is only as fresh as its data cutoff. OceanAlt's responses carry the data coverage date instead of leaving you to guess.
Where to start: free address check · API docs · watch an address
Boundary of everything above: a screening "clear" only means no match in the data held, never a safety guarantee; this page is not legal or compliance advice.