Really nice explanation of a helpful posting utility program! I'm not familiar with Elvish but perhaps I'll look into it. I usually write these kind of things as a web page with some simple template HTML and CSS, adding the functionality with javascript. I guess we all use whatever we're most familiar with.
Once again, great post and thanks for sharing! :)
Originally I wanted to write this in HTML/CSS/Javascript as well... But then I realised that this is something that involves web requests, so that means I'll have to do it on the server side or I'll probably get a bunch of CORS problems. Unless I build a web browser extension for it, but I'm even more unfamiliar with that :P
Thanks for reading!