They are different fields
A hashtag is a #word in the title or the description. YouTube can show a few of them above the title, and the word links to other videos that used it. A tag sits in the tag box, which viewers do not read. YouTube's own help says tags are a minor signal, mostly useful when people misspell the topic.
Filling one of those fields does not fill the other. The caption generator drafts description text and hashtags from words you type. The tag generator builds the tag box and keeps the combined list inside 500 characters.
The published hashtag rule is 60
YouTube's help page on hashtags says that if a video or playlist has more than 60 hashtags, YouTube ignores every hashtag on that video. The extras are not the only ones dropped. The whole set is ignored. Hashtags also have to match the video. Unrelated tags are a misleading-metadata problem, not a growth trick.
More than 15 can already look spammy. That is a caution, and the hard rule to remember is 60. The generator counts the hashtags in the text you paste and names that rule on the result.
Count the description in bytes
The description field holds 5,000 bytes, not a loose pile of characters. Letters in the basic Latin set are one byte. Emoji and many accented letters cost more, so a caption that looks short can still cross the limit. The generator's YouTube check counts UTF-8 bytes for that reason.
Put the promise in the first lines, because that is what people see before they click more. Add chapter times only when you know them, starting at 0:00. This tool does not invent timestamps. A few hashtags can sit at the end of the description, after the sentences.
A hashtag count is not an engagement rate
Nothing in the tag box or the hashtag line tells you whether viewers liked the video. Likes plus comments, divided by views, is a different number. The engagement rate calculator does that division from counts you paste in. It still does not show click-through rate or average view duration. Those stay in YouTube Studio.
When the packaging of the videos you already published is the problem, the free channel audit reads public titles and descriptions. Paid plans keep the written fixes. Pro is $9 a month, Growth is $19, and Unlimited is $39. You can cancel in Settings.
Questions
Do YouTube hashtags replace tags?
No. Hashtags go in the title or description and can show above the title. Tags go in the tag box and mostly help with misspellings and close variants.
What happens if I add more than 60 hashtags?
YouTube ignores every hashtag on that video, not only the ones past 60. Keep a few that name the video.
Does the description limit count emoji as one character?
The limit is 5,000 bytes. An emoji costs more than one byte. The YouTube check on the caption tool counts bytes.