An extremely simple webpage which randomly determines whether you should administer a reward based on a target intermittent reinforcement percentage.
Intermittent reinforcement is the delivery of a reward at irregular intervals, a method that has been determined to yield the greatest effort from the subject. The subject does not receive a reward each time they perform a desired behavior or according to any regular schedule but at seemingly random intervals. (Source)
Dr. Andrew Huberman, a neuroscientist at the Stanford University School of Medicine, explains why and how you might use this in his podcast episode How to Increase Motivation & Drive. He offers some additional practical advice in this interview.
https://schreifels.github.io/intermittent-reinforcement-generator/?pct=60
(This will result in a reward 60% of the time. Update the "60" in the URL to whatever value you like.)