When following ink getting started tutorial at https://use.ink/getting-started/running-substrate I am stuck at one of the steps.

After starting contracts node in dev mode with the following command:

substrate-contracts-node --dev

I am trying to connect to UI via https://contracts-ui.substrate.io/ choosing local node. Getting

Could not connect to ws://
Make sure you are running a local substrate-contracts-node.
substrate-contracts-node --dev

I tried switching off ufw but it didn't help.

I found similar question here but there problem was missing --dev switch, which is not the case here, I pass --dev explicitly.

This is the output of my node console

2023-11-13 09:46:10.415  INFO main sc_cli::runner: Substrate Contracts Node    
2023-11-13 09:46:10.416  INFO main sc_cli::runner: ✌️  version 0.33.0-unknown    
2023-11-13 09:46:10.416  INFO main sc_cli::runner: ❤️  by Parity Technologies <[email protected]>, 2021-2023    
2023-11-13 09:46:10.416  INFO main sc_cli::runner: 📋 Chain specification: Development    
2023-11-13 09:46:10.416  INFO main sc_cli::runner: 🏷  Node name: cool-jellyfish-4492    
2023-11-13 09:46:10.416  INFO main sc_cli::runner: 👤 Role: AUTHORITY    
2023-11-13 09:46:10.416  INFO main sc_cli::runner: 💾 Database: ParityDb at /tmp/substrateeTNwIZ/chains/dev/paritydb/full    
2023-11-13 09:46:11.566  WARN main sub-libp2p: Can't listen on /ip6/::/tcp/30333 because: Other(Custom { kind: Other, error: Custom { kind: Other, error: Other(Left(Left(Left(Left(Right(Transport(Os { code: 97, kind: Uncategorized, message: "Address family not supported by protocol" }))))))) } })    
2023-11-13 09:46:12.660  INFO main sc_rpc_server: Running JSON-RPC server: addr=, allowed origins=["*"]    

How the debug why it is not running as it should?

  • Which browser are you using? I think some of them blocks access to not secure websockets ws://. You should allow that in the browser's config. Nov 16, 2023 at 14:18
  • I am using Brave, tried on Firefox now and it does work! Please post your comment as an answer so I can accept it.
    – jangorecki
    Nov 16, 2023 at 15:32

1 Answer 1


Some browsers do not allow access/connection to not secure websocket (ws://) so you need to allow that by changing your browser's configs.

(OP and I use firefox and it works without changes)

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