Free tool
YouTube description generator
Drafts a description that leads with the promise, then a chapter stub and a place for a related link. Replace the placeholder timestamps before you upload.
What to edit before you paste it
YouTube shows roughly the first 150 characters before "more". That preview should stand alone. Then add real chapter times, starting at 0:00, on videos long enough to need them. Link one playlist or the previous video. Three hashtags is enough; more than 15 and YouTube ignores all of them.
Pair this with a title that makes the same promise.