What it shows you
Each platform draws its interface over your video: a column of buttons down one side, the username and caption along the bottom, controls at the top. Anything underneath is invisible to the viewer no matter how carefully you placed it. Switch a platform on and the shaded areas are the parts it covers. Switch on "safe on all four" and you get the rectangle that clears every one of them — which is the region to keep caption text inside if you want one export to work everywhere. It sits high and to the left of centre rather than in the middle, because the button column and the caption block are not symmetrical.
Why a picture beats a number
You can read that TikTok covers 320 pixels at the bottom, and it still will not tell you whether YOUR caption survives, because that depends on the size you set, the line breaks you got and where the speaker’s head is. Putting a real frame under the overlay answers the actual question in about four seconds. Export one still from the clip you are working on and look.
Nothing leaves your browser
The image is read with the browser’s own file reader and drawn straight to a canvas. There is no upload, no request to a server, and no copy kept — closing the tab is the whole cleanup. That is not a privacy promise so much as a description of how the page is built, and you can confirm it in your browser’s network panel.
The numbers behind the overlay
Zone sizes are as of August 2026 and drawn against a 1080 x 1920 frame: TikTok roughly 100 top, 140 right, 320 bottom; Instagram Reels roughly 220 top, 130 right, 430 bottom; YouTube Shorts roughly 90 top, 60 right, 250 bottom. Platforms move these without announcing it — TikTok added a button at the bottom-right in January 2026 — so treat them as good working rules and check a real frame when a caption matters.
Questions
What is the safe zone for TikTok, Reels and Shorts?
A rectangle of about 865 x 980 pixels inside a 1080 x 1920 frame, 270 down from the top and 65 in from the left, clears all of them. Individually, Meta’s unified Reels area on Instagram and Facebook takes the most vertical space, TikTok is tightest on the right edge, and YouTube Shorts covers the least — though its bottom overlay grows when a viewer expands the description.
Does this upload my video?
No. It takes a still image, reads it in your browser and draws it on a canvas. Nothing is sent anywhere and nothing is stored. You can watch the network panel while you use it.
Can I check a whole video?
Not here — this works on a single frame, which is enough for placement because captions sit in the same region throughout. Export a still from a moment where a caption is on screen and use that.
Basic includes the whole workflow.
Import a source, generate clips, review every one and publish to your own connected channels. Upgrade when you need more.