A client called a coordinator is in charge of monitoring validator nodes on the blockchain network to make sure the information is accurate. Blockchains serve as decentralized distributed ledgers that store transaction data that must be confirmed by a network of validator nodes operating on a decentralized basis. The functionality of various blockchains differs widely.
The data must be consistent amongst all network nodes. Since transactions are recorded on the blockchain and used by validator modes to verify the accuracy of their copy of the ledger, a coordinator is in charge of providing milestones. Not all blockchain systems use coordinator clients.