When using the online Remix IDE, the Run tab has default values of Environment="JavaScript VM" and Account=<a list of addresses I don't own that already have 100 ether each>. What exactly is this environment? Is it a private (test) network that gets set up each time I refresh the browser (which would explain how it seems to be able to simply give me ether to play with) or something else?

2 Answers 2


From the docs, for the JavaScript VM environment:

transactions will be executed in a sandbox blockchain in the browser. This means nothing will be persisted and a page reload will restart a new blockchain from scratch, the old one will not be saved.

So, yes, Remix uses a private blockchain and accounts by default that you can use for testing.

  • Any idea on how to query that blockchain for things like current block number? Oct 27, 2018 at 19:21

I can't comment, so here's an updated link to the docs mentioned above.

For connecting to a sandbox blockchain in the browser. The Remix VM (previously called JavaScript VM) is its own “blockchain” and on each reload the old chain will be cleared and a new blockchain will be started. The old one will not be saved. The London refers to the London fork of Ethereum.

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