What sort of metadata should I include on my site for rich previews in iMessage?

Question

As you can see in this screenshot taken from Apple’s iOS 10 preview page, the Messages app in iOS 10 will offer inline previews of URLs that are sent in conversations:

How can I ensure that my site appears properly in this context? Is there any official documentation from Apple about the specific metadata they’re using to generate these previews?

Answer 1

It's at least using Open Graph and Twitter Card.

Demos

Open Graph

Markup:

<meta property="og:image" content="https://www.j-26.com/assets/facebook.jpg"/>

Preview:

---

Twitter Card

Markup:

<meta property="og:image" content="https://www.j-26.com/assets/twitter.jpg"/>

---

Notable findings

I tested this page using Twitter Card and Open graph and iOS seemed to prefer Open Graph. On the page, the Twitter Card markup is placed before the Open Graph markup and the image used in Twitter Card is smaller than the one used in Open Graph.