So a service that provides metadata for URLs. Caption, description, user ratings, review.

A browser plugin could respond to hovering over a link by querying the service and displaying the response.

Being crowd-sourced, there would have to be some form of contributor reputation tracking.

  YouTube link -> Cats react to bananas [83%; funny, cute]
  Clickhole link -> Infinitely recursive self-parody of clickbait articles [71%; funny]
  Kotaku link -> Gamers overreact to accusations of sexism [43%; news]
  NYT link -> Anticonvulsant drug found effective against Alzheimers [91%; news, advertisement]
  Vimeo link -> Police arrest Black Lives Matter protesters in St. Louis [43%; news, violence, NSFW]