ReadabilityKit is an open source library submitted by Igor Zaplenetev that allows you to quickly gather the relevant data to create previews from a URL.
ReadabilityKit allows you to extract the title, description, top image, top video, and keywords from a remote URL using simple functions. Compared to other libraries the algorithm used by ReadabilityKit works with more urls.
This animation from the readme shows a previewing example:
You can find ReadabilityKit on Github here.
A handy library for previewing urls.