Not sure if this is the right place but does anyone know the name of the tool used to fasten a crank bolt to the bike- mine keeps coming loose (yes ik I need a new one)

what kind of pedals do you have?

Welcome to the forum.
Your post comes confused me. Your title mentions a pedal, but the text mentions a crank bolt, which does not even connect to said pedal.

The bikes I deal with have aluminum cranks. If one of these bikes is ridden for any length of time with a loose crank, the hardened steel spindle of the bottom bracket will deform the soft aluminum shape of the crank such that it will never stay tight again.

Yo might mention the brand/model/year (or some of that) to help better determine what you actually mean.
The pedal is what you put your foot on and screws to the crank/arm.
The crank/arm "Big End" attaches to the Bottom Bracket (BB). Method of attachment differs. THAT'S very important to know.
1 piece crank or ??

This may help identify what you have-
https://www.parktool.com/en-us/blog/...&area%5B%5D=51

If it's a square taper axle then you'll usually need a 14 mm or 15 mm socket or an 8 mm Allen key.