Look up a transaction and its receipt on Ethereum, Base, Arbitrum, Optimism, Polygon, or BNB Chain: status (success/reverted/pending), from/to, value, block, nonce, gas used and price, log count, and any contract created. Public JSON-RPC, no API keys. POST a JSON body like: {"chain":"base","hash":"0xb498053e345acd227657ef2e3de7d9fd9b861d673368419c4b18cfaea20365c8"}