Webmentions

Webmention is an open standard that lets one site notify another when it links to it. When someone replies to, likes, or links one of your posts from their own Webmention-enabled site, they can send your blog a notification so you know about the mention.

Lamb can receive webmentions, and send them when you publish a post that links to other sites.

How it works

Lamb exposes a /webmention endpoint. Other sites discover it two ways:

  • An HTTP Link: <…/webmention>; rel="webmention" header on every page.
  • A <link rel="webmention" href="…/webmention"> tag in your page <head>.

When a sender POSTs a source (their page) and target (your post URL) to the endpoint, Lamb:

  1. Checks that target is a real post on your site.
  2. Fetches the source page and verifies it actually links to target.
  3. Stores the verified mention against the post.

Senders that don’t follow the rules are rejected: a missing or non-http(s) source/target, a target that isn’t one of your posts, or a source that doesn’t link back all return 400. If a previously received source is re-checked and no longer links to the target, the stored mention is removed.

Seeing your mentions

Received webmentions appear at the bottom of the relevant post page, visible to the logged-in author only. Lamb treats them as a private notification for you rather than public comments, so they are not displayed to visitors. Each entry links to the source page, with the author and a short snippet where they can be detected.

Sending

When you publish or edit a post, Lamb scans its rendered HTML for links to other sites and queues a webmention for each. The queue is worked through on the next /_cron run rather than during the publish request, so saving a post stays fast. For each queued target Lamb:

  1. Fetches the target page and discovers its webmention endpoint (HTTP Link header → <link rel="webmention"> → <a rel="webmention">).
  2. POSTs your post URL (source) and the linked URL (target) to that endpoint.

Each source/target pair is sent once — re-editing a post does not re-notify targets it already reached, so receivers are not spammed. Drafts and posts ingested from other feeds do not send webmentions.

Scheduled posts are queued when you save them, but nothing is sent until the publication time has passed — the first /_cron run after the post goes live delivers its webmentions, once the post is publicly reachable for receivers to verify. Editing a scheduled post before it publishes updates the queue (removed links are dropped), and deleting it cancels the queued mentions entirely.

  • Reply posts: Mark a post as in-reply-to another URL — the most common webmention type.
  • Micropub: Publish posts from any Micropub client; uses the same IndieWeb discovery pattern.
  • Cron / scheduled tasks: How /_cron drives feed ingestion and outbound webmentions.
  • Scheduling posts: Scheduled posts send their webmentions when they go live.
  • Cross-posting: Pull posts in from other feeds.
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