Preferred Block Explorers.
Block explorers allow you to explore any transaction in any block that has already been mined and is currently attached to the Bitcoin blockchain. Using a Bitcoin block explorer, you can check the history of any public Bitcoin address and audit how many transactions it has received, its balance, etc. Through a Bitcoin block explorer, you can see the status of mempool, where you will find a total number of unconfirmed transactions along with transaction details. Some advanced block explorers also record how many double spend Bitcoin transactions were done in the last 10 minutes.