It's actually pretty easy to tell the parameters they take if you look at the url for the route.

For:

    story GET   /story/:id(.:format)  story#show

You get

    story_path(id)
    story_path(id, format)
    story_url(id)
    story_url(id, format)

In practice it doesn't cause as many problems as you think, even in large applications.