I've seen it noted in various places recently (mailing list, IRC, personal experience) that the situation after installing a tool installer plugin is suboptimal.

The JSON file containing the installation information for that tool is only downloaded periodically (daily?) along with all other tool installer data.

Ideally, users should not have to wait up to 24 hours (or use a workaround: Manage Plugins > Advanced > Check Now) before they can use these plugins.

So, whenever a DownloadService.Downloadable is loaded into Jenkins, it should fetch the corresponding JSON file from updates.jenkins-ci.org, if necessary.