Deepnote server failed to start

[felixhoffmnn]

Environment data

• VS Code version: Flatpak (v1.105.1)
• Jupyter Extension version (available under the Extensions sidebar): N/A
• Python Extension version (available under the Extensions sidebar): 2025.16.0
• OS (Windows | Mac | Linux distro) and version: Fedora Silverblue 43
• Python and/or Anaconda version: 3.13 and 3.12 (tried both)
• Type of virtual environment used (N/A | venv | virtualenv | conda | ...): uv venv
• Jupyter server running: N/A

Expected behaviour

The Deepnote server starts allowing Deepnote to select the correct kernel and run code.

Actual behaviour

When selecting the Deepnote Server logs, it does not even show anything.

=== Deepnote Kernel Error Report ===

Error Type: _j
Message: Deepnote server failed to start within 120 seconds

Technical Details:
Server URL: http://localhost:8888
Timeout: 120000ms
Server process started but health check failed
The server process may still be starting or may have crashed silently

Troubleshooting Steps:
1. The server may be slow to start - try waiting a bit longer and reloading
2. Check the Output panel for server startup logs
3. Ensure no firewall is blocking localhost connections
4. Check that port is not being blocked by security software
5. Verify Python and deepnote-toolkit are correctly installed
6. Try closing other resource-intensive applications
7. Reload the VS Code window (Cmd/Ctrl+Shift+P → "Reload Window")
8. If the issue persists, report it with the error details

Steps to reproduce:

[NOTE: Self-contained, minimal reproducing code samples are extremely helpful and will expedite addressing your issue]

1. Install VS Code Flatpak
2. Install mentioned extensions
3. Setup a venv with uv
4. Try to open a Deepnote notebook

Note:

When I first install deepnote-toolkit[server] I am able to start the server manually (uv run deepnote-toolkit) and the VS Code Deepnote extension is then able to connect to it and run stuff. So the issue seems to be that the server does not start at all when just using the VS Code extension.

Logs

See above.

[felixhoffmnn]

Not yet sure if it's related to the server not starting, but I am also getting this error message when starting VS Code:

23:27:43.282 [error] Error in activating extension, failed in $A Error: Extension 'Deepnote.vscode-deepnote' CANNOT use API proposal: notebookKernelSource.
Its package.json#enabledApiProposals-property declares:  but NOT notebookKernelSource.
 The missing proposal MUST be added and you must start in extension development mode or use the following command line switch: --enable-proposed-api Deepnote.vscode-deepnote

[Artmann]

Thanks for the report! We will investigate 🕵️

[Artmann]

Hi @felixhoffmnn ! Can you expand on how you set up the venv using uv? Normally, we handle creating the venv from one of the Environments.

What venv is your environment pointing to?