The getbestblockhash RPC returns the header hash of the most recent block on the best block chain.
getbestblockhash none
*bitcoin-cli help getbestblockhash
getbestblockhash
Returns the hash of the best (tip) block in the longest blockchain.
Result:
"hex" (string) the block hash hex encoded
Examples:
> bitcoin-cli getbestblockhash
> curl --user myusername --data-binary '{"jsonrpc": "1.0", "id":"curltest", "method": "getbestblockhash", "params": [] }' -H 'content-type: text/plain;' http://127.0.0.1:8332/