A simple RPC monitor that provides output to both the console and via an HTTP interface.
yarn run:monitor --ws ws://localhost:9944 --port 8181
Then just doing a get on localhost:8181 should return something like
{"blockNumber":7030,"blockTimestamp":"2018-11-27T09:51:06.283Z","elapsed":1.828,"ok":true}
If you are installing it globally -
$ yarn global add @polkadot/monitor-rpc
$ polkadot-js-monitor ...