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.
If you want those words judged against videos you already published, run the channel audit.