> For the complete documentation index, see [llms.txt](https://b-method.gitbook.io/training-resources-for-atelier-b/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://b-method.gitbook.io/training-resources-for-atelier-b/guides-and-tutorials/extending-atelier-b.md).

# Extending Atelier B

Atelier B 4 allows running “external tools” from within the GUI. Several kinds of external tools can be integrated:

* **project external tools**. Those tools are running on a project, and appears in the “Project” menu of the GUI. For instance, they can be used to provide metrics on a project
* **component**. Those tools are running on a component, and appears in the “Component” menu of the GUI. They are launched on the selected component(s)
* **po**. Those tools are running on a selected proof obligation in the interactive prover
* **goal**. Those tools are running on the current goal of the interactive prover

Integrating an external tool is done by writing a “*.etool*” xml file. 

This file describes the type of tool, as well as the command that will be started. This file should be located in the “*extensions*” subdirectory of the Atelier B installation, and is loaded when the Atelier B GUI start. 

For each “etool” file, a corresponding menu entry is created within the “Project” or “Component” menu of the GUI. 

When the menu is clicked, the tool is launched, and the corresponding task appears in the “Tasks” window of Atelier B. Double-clicking on the task displays a windows showing the output of the tool.  The complete syntax of the “*.etool*” files is first described. Then some examples are presented.