So, it's been years and this is still a mistery.

Long story short, how did this guy make the preview image a gif?
http://steamcommunity.com/sharedfiles/filedetails/?id=284538302&searchtext=
Despite being a simple code by itself, it’s got thousands of subscribers proably only for the animated image preview (some people even admit to it in the comments), he is a capable coder as I could see from a collection of his (even if almost all of the addons aren’t his), but from my expiriences on uploading addons I see no possible or conceivable way to make a GIF as thumbnail, it blows my mind thinking of ways one could do that, I tried searching online with no avail, I saw all the comments and it’s just him messing with other people calling it magic, laughing at people mad at him for not saying it and him saying that it’s to “protect the gmod community” as if he was the chosen one or something, I skimmed through every part of the addon and not even a trace, and his profile is private probably not accepting friend requests at all, then going silent on all of steam.

TL,DR: HOW DID HE PUT A GIF AS IMAGE PREVIEW?

Who knows, maybe someone who knows him will read this, maybe someone with expirience or he himself will come out, as far as I know, that’s the only GIF in the whole workshop.
Also, downloading the image shows that it is in fact a GIF and not some black magic fuckery, it’s also 3.7 MB which is over the upload limit.

considering hes a gmod dev he probably just used the steamworks partner api which accepts gifs

https://partner.steamgames.com/doc/features/workshop/implementation - Full workshop implementation guide

EDIT: You can upload GIF’s via the website but you cannot have it look like willoxes without some trickery

Well that’s… odd, if it’s possible, and there’s supposedly an explanation, why don’t more people do it? I’m sure there are capable enough people, but is it really possible without being a developer of the game itself? (also he could have just said that he was a developer instead of just toying with other people)

Because Willox is a wizard.

I think the issue is that gmpublish only accepts .jpg files.

In theory it might be able to recreate gmpublish as, unless im blind, there are no checks on the steamworks api (no key needed) as the checks are done by the publisher on partner.steamgames.com

It might accept gifs with a jpg extension and then play them anyway. Just a guess.

I figured out how to do it a while ago but I’m banned from the workshop

Also Willox did it before he worked at fp so it’s not like it’s a developer only thing