I am trying to save some data into a block. The extraData field has a constant value since block 1. Also where does the data parameter of sendTransaction() function get stored?

1 Answer 1


Please find reference in this answer here: What does each genesis.json parameter mean?

Excerpt here: "extraData An optional free, but max. 32-byte long space to conserve smart things for ethernity."

  • Or, to paraphrase, you can put anything you want in the extraData field.
    – lungj
    Jul 16, 2017 at 22:44
  • 1
    Some mining pools use it for logging their blocks. Sep 21, 2018 at 10:18

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