# Running nbdiff-web via Port Proxying in RenkuLab

**URL:** <https://renku.discourse.group/t/running-nbdiff-web-via-port-proxying-in-renkulab/1171>\
**Category:** RenkuLab\
**Created:** [19 August 2025 06:17 UTC](https://renku.discourse.group/t/running-nbdiff-web-via-port-proxying-in-renkulab/1171 "2025-08-19T06:17:00Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![cimeister](https://yyz2.discourse-cdn.com/free1/user_avatar/renku.discourse.group/cimeister/32/881_2.png) [@cimeister](https://renku.discourse.group/u/cimeister)\
**Post date:** [19 August 2025 06:17 UTC](https://renku.discourse.group/t/running-nbdiff-web-via-port-proxying-in-renkulab/1171/1 "2025-08-19T06:17:00Z")

</div>

I’m setting up a course using Renku and would like to enable students to view structured notebook diffs using `nbdime` and specifically the `nbdiff-web` interface (using the basic `nbdiff` command works, outputting a written diff to the terminal). The goal is to run something like:

```auto
nbdiff-web notebook1.ipynb notebook2.ipynb --port=8899 --ip=127.0.0.1

```

inside a RenkuLab session, and then access the visual diff via the browser.

From what I understand, `jupyter-server-proxy` should make this possible via a URL like:

```auto
/proxy/8899/

```

However, this URL returns a 404 when accessed within the session or when appended to paths like:

```auto
https://renkulab.io/user/<username>/<project>/proxy/8899/

```

I’ve confirmed that:

- `nbdiff-web` is running and listening on `127.0.0.1:8899`

- The terminal process is active

- RenkuLab is using JupyterLab and supports `jupyter-server-proxy` (output of `jupyter serverextension list` shows `jupyter_server_proxy enabled OK`)

But I can’t get the web interface to load. I also noticed that `JUPYTERHUB_SERVICE_PREFIX` isn’t set in the environment, so generating the path programmatically doesn’t work.

### **Questions:**

1. What is the correct URL path to access a service like `nbdiff-web` running on a specific port inside a RenkuLab session?

2. Is there a recommended way to use `jupyter-server-proxy` with custom services in RenkuLab?

Thanks so much, and I’d be happy to share a working example back with the community once this is solved!

---

<div class="post-metadata">

**Author:** ![leafty](https://yyz2.discourse-cdn.com/free1/user_avatar/renku.discourse.group/leafty/32/796_2.png) [@leafty](https://renku.discourse.group/u/leafty)\
**Post date:** [19 August 2025 06:36 UTC](https://renku.discourse.group/t/running-nbdiff-web-via-port-proxying-in-renkulab/1171/2 "2025-08-19T06:36:20Z")

</div>

Have you considered using the git extension in JupyterLab? It should already be installed and it uses `nbdime` to show notebook file diffs.

 ![Screenshot 2025-08-19 at 08.30.45](https://global.discourse-cdn.com/free1/uploads/renku/original/1X/54bd85b64d08f85d60dbe6b12b12c4d07a6a70da.png)

The git extension is accessed by clicking the git icon on the left-hand side of the Jupyter interface and selecting a notebook file in the git status panel should show a diff handled by `nbdime`.