TikTok gives you 4,000 characters and shows about 100

Drop a caption in the box above and the counter measures it against TikTok's current 4,000-character limit, marking where the visible window ends. It runs locally, so nothing about your unreleased video leaves your device.

Counts for the other nine platforms update at the same time, which matters if the same clip is going to Reels and Shorts with the same caption.

TikTok raised its caption limit from 150 characters to 4,000, and most creators still write as though the old limit applied. The extra room is worth using, because TikTok reads caption text: it feeds search and recommendations, so a caption that names its topic in plain language gets found by people typing that topic into the search bar.

What has not changed is the visible window. About the first 100 characters sit over the video before the caption collapses, and the video is competing with that text for the same attention. Write the first line as the hook, then use the remaining space for context, keywords, and the question you actually want answered in the comments.

TikTok does not publish a hard hashtag cap, but hashtags share the 4,000 characters with your caption. Three to five specific tags is a workable default. Long tag walls push your own words out of the visible window and buy nothing in return.

Your bio is a separate and much tighter 80 characters, the shortest of any platform WriteOnce supports. That is one sentence, so it has to do exactly one job: say who the account is for. Pinned videos carry everything else, which is why TikTok bios that try to list credentials always read as cramped.