Using web3 to connect to a geth's node rpc API, is there a way to detect when a block has been mined by a specific node? The only way I've found so far is to redirect the node's console output to a file and parse that file. Is there a better way?

FYI - All the nodes are mining to the same public address so I can't use the miner property of a block.

1 Answer 1


One way to do it is to let each miner set their own 'extraData' field, as described in the documentation:

--extradata value         Block extra data set by the miner (default = client version)

This can be quickly shown by typing


on geth console.

Note: the output is in hexadecimal format, which can be converted into readable format with

  • Yeah, I have discovered that option a few hours ago. I'll give it a try, but the miner I'm using is actually a fork of geth supporting a different blockchain implementation. I'm not sure they will honor this configuration. If not do you have any other idea? How does the miner knows when it mined a block successfully? I'd like to tap directly into that process if possible. Could I spy on the peers connection traffic to check if the miner tried to broadcast a block?
    – plalx
    Apr 17, 2018 at 15:11
  • Hmm...detecting block broadcast is likely to be messy: what happens when a block is orphaned, or becomes an uncle? Apr 17, 2018 at 23:04
  • I confirmed that it works with the other blockchain, thanks. Also, any idea how to put a public address in there? I'm limited by the 32 chars limit. I've worked around the limit by converting to base64, but I'm sure there's a better way?
    – plalx
    Apr 18, 2018 at 4:28

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