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. A few hashtags is enough. More than 15 can look spammy, and above 60 YouTube ignores every hashtag on the video. YouTube hashtags vs tags separates those from the tag box. The caption generator counts the description in bytes.
Pair this with a title that makes the same promise. The channel description, the text in the header and on About, is a different field with a 1,000-character cap in the Data API. The bio generator drafts that one.