# Custom handlers in JupyterLab

**URL:** <https://discourse.jupyter.org/t/custom-handlers-in-jupyterlab/8850>\
**Category:** JupyterLab\
**Tags:** jupyterlab, how-to, help-wanted\
**Created:** [April 20, 2021, 5:35pm UTC](https://discourse.jupyter.org/t/custom-handlers-in-jupyterlab/8850 "2021-04-20T17:35:25Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Nikola\_Staykov](https://yyz1.discourse-cdn.com/flex031/user_avatar/discourse.jupyter.org/nikola_staykov/32/4171_2.png) [@Nikola\_Staykov](https://discourse.jupyter.org/u/Nikola_Staykov)\
**Post date:** [April 20, 2021, 5:35pm UTC](https://discourse.jupyter.org/t/custom-handlers-in-jupyterlab/8850/1 "2021-04-20T17:35:25Z")

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Hello, I am trying to migrate from `jupyter notebook` to `jupyter lab`. I cannot find the right way to use a custom handler as described here: [Custom handler documentation](https://jupyter-notebook.readthedocs.io/en/stable/extending/handlers.html).

1. When I hardcode the custom handler in the jupyter config file it doesn’t get read.
2. When I pass it as an argument to the ‘jupyter lab’ command it breaks with:  
File “d:\program\_files\anaconda3\envs\perper\lib\site-packages\traitlets\config\loader.py”, line 681, in load\_config  
[2021-04-20T17:33:27.805Z] raise ArgumentError(“Invalid argument: ‘%s’”%raw)  
[2021-04-20T17:33:27.806Z] traitlets.config.loader.ArgumentError: Invalid argument: ‘–NotebookApp.nbserver\_extensions’

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**Author:** ![adpatter](https://yyz1.discourse-cdn.com/flex031/user_avatar/discourse.jupyter.org/adpatter/32/21229_2.png) [@adpatter](https://discourse.jupyter.org/u/adpatter)\
**Post date:** [April 20, 2021, 8:14pm UTC](https://discourse.jupyter.org/t/custom-handlers-in-jupyterlab/8850/2 "2021-04-20T20:14:59Z")

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I noticed that you didn’t mention the Jupyter Sever documentation, so I thought I should post it here: [Documentation for Developers — Jupyter Server 1.7.0.dev0 documentation](https://jupyter-server.readthedocs.io/en/latest/developers/index.html)

Perhaps that could be implemented as an extension?