# 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. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://b-method.gitbook.io/training-resources-for-atelier-b/guides-and-tutorials/extending-atelier-b.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.