# Create and use your own custom Flow Builder steps

The Call Function step offers the possibility to add your own custom step to your flow. 

Use the Functions Editor to create, edit and test your function! Once you’ve done this, you can use your new function inside Flow Builder via the Call Function step. 

 

### Using the functions editor

Write functions in [NodeJS](https://nodejs.org/) (a JavaScript runtime). Functions can also make use of third-party, public [NPM](https://www.npmjs.com/) modules.

All functions follow the same basic pattern:

1. The function received inputs. These can be variables from your flow.
2. There is an internal logic. The inputs are parsed and we do the custom step logic.
3. An output is returned. This output is available as a variable in your flow.


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