Discovering interfaces for web services

Chris recently posted an interesting idea - maybe web services should disclose information about the clients (and their versions) which access them:

It’s not always obvious whether a client library is still compatible with the web service it was developed for. I’ve seen this before with flickr libraries and came across it again a couple of weeks ago when playing around with Amazon Simple DB.

and then

If the provider was to publish this information (cient name/version, total requests, date of last request and probably some other useful info) then it should be possible to see which libraries still work with the web service. Does anyone do this? Does it actually sound like a sensible idea?

I think it sounds like a fine idea, and the primary example that springs to mind is Twitter, which links information about the source of each tweet in their web interface. It’s a useful piece of information about what tools people are using to interact with the service, and can often be used to ‘discover’ new (and maybe better) interfaces.