Before being listed in Tool Library, tools that you submit in XrmToolBox portal are validated. You will find below a check list of items to consider to ensure your tool will be validated.

Nuget package checklist

Submitting a well configured package is essential for tools discoverability and to ensure tools can be listed and updated throug Tool Library.

Validation steps
My Nuget package has an Icon url

My Nuget package has a Project url

My tool library is included in my Nuget package under a "Plugins" folder

My tool library version is the same that my Nuget package version

Tool checklist 

Validation steps
My tool has a dedicated image for Large tool display mode in Tools list
My tool has a dedicated image for Small tool display mode in Tools list
My tool adapts its controls size when I resize XrmToolBox main application to fit to the available size
My tool can be opened without an organization connected
Without an organization connected, tools controls can be used without any error
Without an organization connected, using controls that requires a connection opens the connection selection dialog
With an organization connected, tools controls can be used without any error
Long running operations are processed asynchronously and the main application is not frozen