"Notebook does not appear to be JSON"

[tobinjones]

I can't get this to work, perhaps I'm doing something wrong.

I create a new jupyterlab installation:

mkdir juviotest
cd juviotest
uv init
uv add jupyterlab juvio

I enable the extension and run jupyterlab

uv run jupyter labextension enable juvio-frontend
uv run jupyter lab

I see two new notebook types, "Juvio Notebook" and "Juvio"

Juvio Notebook
If I create a notebook of type "Juvio Notebook", I see a file called untitled.juvio is created. If I look at it on disk, it is blank. When I try to open it, I get the error:

File Load Error for untitled.juvio
Unreadable Notebook: <snip>/testjuvio/untitled.juvio NotJSONError("Notebook does not appear to be JSON: ''")

Juvio
If I create a notebook of type "Juvio", I see a file called Untitled.ipynb is created. On disk it has the contents

{
 "cells": [],
 "metadata": {},
 "nbformat": 4,
 "nbformat_minor": 5
}

It opens fine in jupyterlab and shows that it's using the "Juvio" kernel.

The cell magic %juvio install antigravity works. I can import antigravity from the notebook (nice!). I notice that on disk, the notebook has been replaced by a script

# /// script
# requires-python = "==3.13.2"
# dependencies = [
#   "antigravity==0.1",
<snip>

However, if I save the notebook from jupyterlab this script is overwritten with a normal JSON notebook. If I don't save, and instead just try to open Untitled.ipynb with jupyterlab I get the error

File Load Error for Untitled.ipynb
Unreadable Notebook: <snip>/testjuvio/Untitled1.ipynb NotJSONError('Notebook does not appear to be JSON: \'# /// script\\n# requires-python = "==3....')

Am I doing something wrong here?

[OKUA1]

Hi @tobinjones, thanks for letting me know. I was able to reproduce the issue, it seems like the server extension is not being picked up correctly. I will investigate it a bit later, as a quick workaround this should work uv run jupyter lab --ServerApp.jpserver_extensions='{"juvio": True}'. Please let me know if it helps.

[ConstantinHvber]

Hi, thank you for your cool project. unfortunately I suffer from the same error, if you need any logs or debugging info let me know

[OKUA1]

Hi @ConstantinHvber. Thanks for confirming the issue. As per my previous message, there seems to be a small bug which prevents the server extension from being picked up automatically. Have you tried running the jupyterlab with an additional argument like suggested above ? jupyter lab --ServerApp.jpserver_extensions='{"juvio": True}'

Please let me know if the problem persists even when using this workaround.

[ConstantinHvber]

Yes the work around is working, thank you

[OKUA1]

Great, thanks for confirming. I have added the workaround to the main readme for now.