"Is not open in the session Code: -32602" multiple requests error in VSCode using Marimo

[edwardmoradian]

Describe the bug

I am regularly getting the same error pop-ups in VSCode using Marimo Notebooks that reoccur even after updating extensions, reloading the window or existing VSCode:

Sample Error 1:
Request textDocument/semanticTokens/full failed.
Message: Document vscode-notebook-cell:/Users/.../.../Home/....py#W0sZmlsZQ%3D%3D is not open in the session
Code: -32602

Sample Error 2:
Request textDocument/codeAction failed.
Message: Document vscode-notebook-cell:/.../.../.../....py#W3sZmlsZQ%3D%3D is not open in the session
Code: -32602

Sample Error 3:
Request textDocument/inlayHint failed.
Message: Document vscode-notebook-cell:/.../.../.../....py#W5sZmlsZQ%3D%3D is not open in the session
Code: -32602

I have reached asked in a thread in the Discord Server for marimo:
https://discord.com/channels/1059888774789730424/1468647354373636218/1468647354373636218

Environment

Details

Replace this line with the output. Leave the backticks in place.

Steps to reproduce

1. Open a Marimo notebook in VSCode
2. Eventually the pop-up starts and does not stop with the errors.

[edwardmoradian]

Editing setting.json with these properties did not work:

{
"[python]": {
"editor.inlayHints.enabled": "off",
"editor.semanticHighlighting.enabled": false
},
}

[manzt]

Thanks for the report!

We have managed language servers (ruff, ty) that run inside the marimo extension, and right now they don't respect VS Code's inlay hint settings.. so even if you've disabled inlay hints in your editor config they'll still show. That's something we need to fix on our end.

For the errors themselves, it would help to know whether they're coming from our managed servers or from an external language server like Pylance or a standalone Ruff/Ty trying to operate on notebook cells. Could you run the "marimo: Show Diagnostics" command from the command palette (Cmd+Shift+P) and paste the output here? That'll help us narrow things down.

[edwardmoradian]

Thanks for the report!

We have managed language servers (ruff, ty) that run inside the marimo extension, and right now they don't respect VS Code's inlay hint settings.. so even if you've disabled inlay hints in your editor config they'll still show. That's something we need to fix on our end.

For the errors themselves, it would help to know whether they're coming from our managed servers or from an external language server like Pylance or a standalone Ruff/Ty trying to operate on notebook cells. Could you run the "marimo: Show Diagnostics" command from the command palette (Cmd+Shift+P) and paste the output here? That'll help us narrow things down.

marimo VS Code Extension Diagnostics

Language Server (LSP):
UV Bin: Bundled (/Users/edwardmoradian/.vscode/extensions/marimo-team.vscode-marimo-0.10.1-darwin-arm64/bundled/libs/bin/uv)
UV: 0.9.26 (ee4f00362 2026-01-15) ✓
Using bundled marimo-lsp via uvx

Python Extension:
Interpreter: /Users/edwardmoradian/Desktop/Home/Git Projects/xyz/.venv/bin/python
Version: 3.10.17
Environment: VirtualEnvironment (xyz (3.10.17))

Python Language Server (ty):
Status: running ✓
Version: 0.0.14 (16597f5e2 2026-01-26)
Python: /Users/edwardmoradian/Desktop/Home/Git Projects/xyz/.venv/bin/python (3.10.17)

Ruff Language Server:
Status: running ✓
Version: 0.11.13

Extension Configuration:
Version: 0.10.1
UV integration disabled: false

System Information:
Host: desktop
IDE: Visual Studio Code
IDE version: 1.109.0
Platform: darwin
Architecture: arm64
Node version: v22.21.1

Common Issues:
1. If notebooks won't open:
- Check Python interpreter is selected
- Ensure marimo and pyzmq are installed
- Check 'marimo-lsp' output channel for errors
2. If features are missing:
- Ensure marimo version is >= 0.19.0
- Try reloading the window

[edwardmoradian]

How can I disable the inlay hints in VScode? I tried the below and the error messages still show:

1. Open Settings (Cmd + ,).
2. In the search bar at the top, type inlay hints.
3. Look for the setting Editor > Inlay Hints: Enabled.
4. Change the dropdown from on to off.

[manzt]

Our managed language servers use a language ID called mo-python (instead of python) to avoid conflicts with Pylance and other Python language servers.

These servers aren't aware of cell-cell dependencies, so they can't provide accurate diagnostics or completions across cells in a reactive notebook like marimo. This means there's a lot more we need to do on our end to provide a rich editing experience, since these existing plugins don't work out of the box with our notebooks.

That's why [python] scoped settings don't apply to marimo cells. You can target mo-python directly in your settings.json:

{
  "[mo-python]": {
    "editor.inlayHints.enabled": "off",
    "editor.semanticHighlighting.enabled": false
  }
}

We'd ideally like to mirror [python] settings automatically (and hide this implementation detail), but the approaches available in the VS Code API are fairly hacky so we're holding off for now.

On the broader problem of getting language servers to understand reactive notebooks, I've started a proposal on the LSP spec to support this: microsoft/language-server-protocol#2224. Ideally this would allow for us to remove mo-python entirely (and a lot of code).