Figuring out what's behind a SPARQL endpoint

What's the best way to get a grip on what's actually behind an endpoint?

I've been mulling over a proof-of-concept project to enrich published legal content - already highly annotated with RDF metadata - with RDF content from open government sources. But I'm kind of baffled by how best to assess the richness of an endpoint other than by running my own SPARQLs - eg. listing DISTINCT predicates, or CONSTRUCTing some of the typed resources.

These queries give me some indication of what's there ... but  what would be handy is some sort of visualisation or analysis tool that gives me statistics like the number of resources contained in the endpoint, the type and predicate vocabularies used, and the density of linking between resources.

Anything like this exist?

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