EnSight allows users to define toolbox items, that are accessed by selecting the User Defined toolbox feature icon. These items are collections of custom Python code that perform common operations. These tools can include full interfaces and can interact with all of EnSight's core features. The mechanism opens up EnSight to specific customization to meet a particular site or individual user's needs.

Tools are written as Python objects that are dynamically loaded from when EnSight starts up. There is a formal mechanism (EnSight Extension Mechanism) through which EnSight users may add their own, custom tools.