I'm trying out the buidler suite using scaffold-eth. I can start up using yarn start fine, but when I run yarn run chain I get the following error:

Error: listen EADDRINUSE: address already in use
    at Server.setupListenHandle [as_listen_2] (net.js:1309:16)
    at listenInCluster (net.js:1357:12)
    at GetAddrInfoReqWrap.doListen (net.js:1496:7)
    at GetAddrInfoReqWrap.onLookup [as oncomplete] (dns.js:69:10)
error Command failed with exit code 1

Looking at yarn run chain in the package.json yields that it moves in to the buidler directory and executes npx buidler node. A cursory look at the error looks like buidler defaults to port 8545, but that port is indeed already in use on my machine.

The answer should be simple enough - I just need to have buidler launch the dev chain on a different port. I've looked through the docs, though, and I'm not finding anything.

How do I tell buidler to use a different port?

1 Answer 1


You can check by running npx buidler node --help:

$ npx buidler node --help                                                              

Usage: buidler [GLOBAL OPTIONS] node [--hostname <STRING>] [--port <INT>]              


  --hostname    The host to which to bind to for new connections (default: "localhost")
  --port        The port on which to listen for new connections (default: 8545)        

node: Starts a JSON-RPC server on top of Buidler EVM                                   

For global options help run: buidler help                                              

As expected, you can just pass a port using --port <your-port>.

  • 1
    I could've sworn I tried --port. Oh well. Thanks! Jun 14, 2020 at 7:47

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