From Bitcoin Wiki
BTCplex allows you to search and navigate the blockchain.
- Browse blocks and transactions.
- Check addresses balance history.
- Search for blocks, transactions, and addresses.
BTCplex provides a full-featured JSON API to access data pragmatically.
- A REST API for acessing blocks, transactions and addresses balance.
- A BlockExplorer.com compatible plain text query API.
- Few server-sent events endpoints to monitor addresses, unconfirmed transactions, and new blocks.