Webmention

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WebMention is a modern reimplementation of pingback using only HTTP and x-www-urlencoded content rather than XMLRPC requests.

Protocol Summary

Assuming Aaron's blog supports receiving webmentions, and Barnaby's blog supports sending webmentions:

User Aaron posts a blog post on his blog
User Barnaby writes post on his blog that links to Aaron's post.
After publishing the post (i.e. it has a URL), Barnaby's server notices this link as part of the publishing process
Barnaby's server does webmention discovery on Aaron's post to find its webmention endpoint (if not found, process stops)
Barnaby's server sends a webmention to Aaron's post's webmention endpoint.
Aaron's server receives the webmention
Aaron's server verifies that target in the webmention is a valid permalink on Aaron's blog (if not, process stops)
Aaron's server verifies that the source in the webmention contains a hyperlink to the target (if not, process stops)

Unmentioned but implied (and vaguely mentioned in the pingback spec):

Aaron's server displays the information about Barnaby's post somewhere on Aaron's post.

See the Webmention Spec for a full description of the protocol.

See comment: how to accept a comment for more details on accepting comments in general and displaying them.

Which links in a post should receive webmentions?

Should you only send a webmention for hyperlinks with a rel value of in-reply-to?
- Only to the first hyperlink with a rel value of in-reply-to?
Should you send webmentions to all URLs in a post?

What do existing implementations do?

I send pingbacks (webmentions coming soon) to the in-reply-to URL if set, and all URLs in the post content field. --Waterpigs.co.uk 09:14, 10 April 2013 (PDT)