Webmention is a W3C Recommendation defining a simple protocol for notifying a URL when it is linked from another site. It enables decentralized cross-site conversations, comments, and reactions on the open web.
WebMention
Webmention is a W3C Recommendation that defines a small protocol for one web page to tell another that it has linked to it. When a source page publishes a link to a target, the source sends a single HTTP POST to the target’s Webmention endpoint with the two URLs; the receiver then verifies the link really exists and can display the mention as a comment, like, or reply. It is decentralized conversation built out of nothing more than links and a form post.
- A single notification - The whole protocol is one
POSTcarryingsourceandtargetURLs — no accounts, no API keys. - Endpoint discovery - Receivers advertise their endpoint via an HTTP
Linkheader or<link>tag so senders know where to send. - Verification - The receiver fetches the source and confirms the link before trusting the mention, which blunts spoofing.
- IndieWeb foundation - It is a cornerstone of the IndieWeb, powering cross-site replies between independent personal sites.
Webmention is deliberately tiny, and that is the lesson it carries into API design: a well-scoped, single-purpose interaction can replace a heavy platform API for a whole class of cross-site behavior. It sits alongside ActivityPub in the open-social stack — ActivityPub federates whole servers, while Webmention handles the lightweight case of “this page mentioned that page.” For anyone building decentralized or agent-mediated communication, it is a clean model of doing one thing over plain HTTP and letting the receiver decide what the notification means.
