Why subscriber count is a bad activity signal
A subreddit with 500K subscribers can be nearly dormant, while a 5K-member community can have daily engaged discussion. Subscriber counts accumulate forever; they don't decay when a community goes quiet. This tool samples actual recent posts to measure what's really happening now.
What 'worth monitoring' means here
The assessment combines how often the community posts, how often those posts get a reply, and (when computable) how quickly. It's a starting signal, not a guarantee of engagement for your specific post — pair it with the Subreddit Rules Checker to confirm the community allows the kind of post you have in mind.