## TL;DR
Widgets showing as text means the frontend never loaded the widget JavaScript, almost always because the `jupyter-widgets` nbextension is missing or disabled. Install `ipywidgets` and `widgetsnbextension` in the same environment that runs the notebook server, then enable the extension with the enable command below and hard-refresh the browser tab. If widgets still render as text after that, the server and kernel are running in different environments.

```text
ipywidgets not rendering: jupyter-widgets nbextension missing
```

## Use this when
- Widget constructors like `IntSlider` or `interact` produce text output such as `IntSlider(value=0)` instead of a control.
- Opening the notebook shows a JavaScript console error about a missing widget manager module.
- The same notebook renders widgets on one machine but not on another.

## Not for this skill when
- Widgets render but stop updating after a kernel restart. That is a closed comm channel, covered by the FloatSlider sync skill.
- Widgets render but raise a version-mismatch warning in the browser console. That is an ipywidgets-vs-frontend version conflict, not a missing nbextension.

## Steps
1. Confirm which environment the server runs in: run `which jupyter` and `jupyter --paths` in the terminal where you started the server. Expected: the config, data, and runtime paths point at the environment you intend to use.
2. Check whether the nbextension is registered: `jupyter nbextension list` and look for `jupyter-widgets/extension` under the config section. Expected: the line shows the extension and whether it is enabled; if it is absent, the package is not installed in this environment.
3. Install the packages into the server environment: `pip install ipywidgets widgetsnbextension`. Expected: pip reports both packages installed with no dependency conflicts.
4. Enable the extension: `jupyter nbextension enable --py widgetsnbextension --sys-prefix`. Expected: output confirming `Enabling notebook extension jupyter-js-widgets/extension` and validation OK.
5. Hard-refresh the notebook browser tab (Ctrl+Shift+R or Cmd+Shift+R) and re-run a widget cell. Expected: the cell output is an interactive slider or control, not its text repr.
6. If widgets still show as text, verify the kernel matches the server: `jupyter kernelspec list` and check the kernel argv points at the same environment's Python. Expected: the kernel's Python path and the server's Python path agree.

## Tool compatibility
ipywidgets 7.x and 8.x with widgetsnbextension 3.x and 4.x; classic notebook 6.x and 7.x, JupyterLab 3.x and 4.x; Python 3.9 through 3.12.

## Variant phrasings
### jupyter widgets showing as text instead of slider
The same missing-extension symptom described by what the user sees. Identical fix.

### widgetsnbextension not enabled
The enable-step phrasing. Run the enable command from step 4 in the server environment.

### ipywidgets IntSlider renders as IntSlider(value=0)
The concrete text-repr symptom. Confirms the frontend widget manager never loaded.

## Why it happens
ipywidgets splits its work in two: the Python side builds widget models in the kernel, and the JavaScript side renders them in the browser. The JavaScript side is delivered as a notebook extension that must be both installed and enabled in the environment running the server. When that extension is missing, the browser has no widget manager, so it falls back to printing the model's text representation. The failure is silent because nothing raises; the cell simply completes with text output, which is why users chase kernel or code bugs first.

## Edge cases / pitfalls
- Enabling the extension in the kernel's environment while the server runs in a different one changes nothing. The nbextension must be enabled where the server runs.
- A plain browser refresh can serve a cached page without the newly registered extension. Use a hard refresh or an incognito window to rule out caching.
- JupyterLab uses labextensions, not nbextensions. If the lab UI is the target, the fix is the `@jupyter-widgets/jupyterlab-manager` labextension, not this nbextension.
- Conda installs of `ipywidgets` sometimes pull an older `widgetsnbextension`. Pin both explicitly if the versions drift.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_S7JMkI-nrcaSmhnm86ppvQ