Webmentions are a protocol for one web page to let another web page know that it’s been linked to. Say I find an article on a blog I admire and want to include a link to it from my blog. If both blogs are Webmention-capable, when I publish my post, my blog sends a Webmention to the blog I linked to, letting them know about the link.
Webmentions originated with the IndieWeb community, who look back on the early days of an open and free web with nostalgia. They dislike that the web has become the dominion of closed platforms like Facebook and Medium, controlled by a small number of corporations. They would like everyone to maintain control over their content by publishing on a platform they own: a web of individual sites hosted on shared hosting, virtual private servers, and dedicated servers under the control of the content creator. Comments and conversations would appear alongside the content and be the content.
In some ways this seems a retrograde move: comments don’t have the importance on the web that they once had. Many publishers are removing comments altogether because they aren’t prepared to invest in moderation and hosting that comments require. Conversations have moved away from individual domains and onto social media platforms like Twitter and Facebook. But the IndieWeb movement feels something important was lost with the decline of comments and conversations between bloggers and publishers, each with their own domain.
One of the major benefits of platforms like Facebook is that they foster conversation and engagement in a way that individual sites do not. Webmentions are intended to act as the thread that links conversations on the open web together. If a writer wants to respond to an article, they can publish a response on their site and the Webmention system will create a web of responses that link together participants of the conversation.
If all that sounds familiar, you’d be right: Webmentions have essentially the same function as the Pingbacks familiar to WordPress users. But Pingbacks had limitations that Webmentions do not, particularly where security is concerned. Pingbacks use the WordPress XMLRPC system, which has been part of WordPress since its earliest days and has been causing problems almost as long, most notably being vulnerable to brute force attacks and helpful for launching distributed denial of service attacks.
Webmentions are a modern implementation: what Pingbacks might have been had they been created today. But users of Pingbacks might remember them for another reason, spam. Any WordPress site with Pingbacks enabled is immediately bombarded with spam Pingbacks. The Webmention spec has little to say about spam, so users who choose to implement Webmentions will have to rely on existing anti-spam technologies like Akismet.