Free tool
YouTube tag generator
Builds a short tag list from your topic, title, and audience. YouTube caps the whole list at 500 characters, so extra phrases are dropped instead of silently truncated mid-word.
What tags are for
Tags help with close variants and misspellings. They do not replace a specific title or the first lines of the description. Repeat the words a viewer would type, including a longer phrase and the shorter pieces of it. Skip dumping unrelated popular words into the list. Hashtags are the #words in the title or description, which is a different field. YouTube hashtags vs tags keeps the two apart, and the caption generator drafts the description side.
If you want those words judged against videos you already published, run the channel audit. The channel description is a different box from the tag list. The bio generator drafts that About text.