Sending webmentions on deploy

I’ve spent a fair bit of time on the receiving end of webmentions, from adding support for them in the first place through to fetching them at build time and rendering them server-side so the discussion section doesn’t flicker in over JS. What I’d never actually done was send the other half. Every link I’ve ever made out to another IndieWeb site has just sat there, silently not telling anyone I’d linked to them. Webmentions are two-sided. When I publish a post that links to someone else’s site, I’m supposed to ping their webmention endpoint to say “hey, I mentioned you”. That’s how IndieWeb replies and references actually close the loop, rather than just being a one-way pull. I’d been shouting into the void for years. Hopefully now some of it gets heard. Hooking into the deploy I’m already using webmention.io to receive mentions, but sending them needed something else. webmention.app has a simple /check endpoint that, given a URL, crawls the page, finds any outbound links, and sends…