  The Ethereum blockchain is essentially a globally replicated public database.
Programs called smart contracts can access this database. Over 10 million smart
contracts have been deployed on the Ethereum blockchain. Executing a method of
a smart contract generates a transaction that is also stored on the blockchain.
There are over 1 billion Ethereum transactions to date. Smart contracts that
are transparent about their function are more successful than opaque contracts.
We have therefore developed a tool (ContractVis) to explore the transparency of
smart contracts. The tool generates a replay script for the historic
transactions of a smart contract. The script executes the transactions with the
same arguments as recorded on the blockchain, but in a minimal test
environment. Running a replay script provides insights into the contract, and
insights into the blockchain explorer that was used to retrieve the contract
and its history. We provide five concrete recommendations for blockchain
explorers like Etherscan to improve the transparency of smart contracts.
