Captions are checked on your device. Nothing you type is sent anywhere.
Limits that matter
Each platform has a hard limit and a softer one. The hard limit is the most it will accept, such as 2,200 characters on Instagram or 280 on X. The soft limit is how much shows before the rest hides behind more, which is often only the first line or two. Put the hook in that first part.
Questions
Why does X count differently?
X counts every link as 23 characters however long it is, and counts most emoji and Chinese, Japanese and Korean characters as two. The checker uses the same rules, so the number matches what X shows.
How many hashtags should I use?
Instagram allows 30, YouTube ignores all of them if there are more than 15, and Threads allows one topic tag. On most platforms a few specific hashtags work better than many general ones, so the checker warns when a caption has a lot.
Do line breaks survive?
Yes, on all the platforms listed. The preview shows your caption with its line breaks and the point where each platform hides the rest. Instagram also hides everything after the second line break, which the preview takes into account.
Is my caption saved?
Your draft is kept on this device so it is still here if you close the tab. Clear the box to remove it.