I would have never guessed how to request the bot, if you didn't show it. That's another reason why I think that there should be a standard way to request bots, it increases discoverability. For contrast, Roboragi:

• {this} looks for anime
• looks for manga
• ]this[ looks for light novel
• |this| looks for visual novel

You probably wouldn't guess it from the fanfic link summary bot either.

I think that a simple common syntax that could be used is @!bot-name [options] ["]data to process["], at least when users are requesting it regardless of community. It's hard to hit it by accident, but still easy to type, and flexible enough to allow multiple bots to follow it. So for example:

• @!fanfic-link-bot ao3 STORYID // looks for STORYID in Archive of Our Own
• @!animanga-bot ln "story name" // looks for a light novel called "story name"
• @!units-converter-bot grams "five cups of flour" // converts five cups of flour into grams
• etc.

Then if community moderators are allowed to call bots to perform functions automatically, without the user requesting them, they could also set up synonyms as shorthands. for example people in c/fanfiction could simply type "ffao3 STORYID" instead, less keystrokes for the same result.