A set of attached extensions is reduced before it is exposed to the code of a processing extension point to which the extensions are attached. An application calls an extension registry to obtain a list of available extensions attached to a given extension point, and filter functionality is integrated into the extension registry. Filters including filtering logic are plugged into the extension registry itself, and the extension registry selects the filter or filters to be applied for a current context. The extension registry defines an extension point to collect filters as extensions and to define an interface that those filters will implement. Each filter specifies when it should be called. As a result, an application can supply a filter that knows what extensions to expose and which to exclude in one or more contexts.