Why context matters for a thumbnail
A thumbnail that looks great on its own can still fail once real UI elements - the caption, username, like and share buttons - sit on top of it. This overlays a mockup of each platform's on-screen UI elements onto your image at roughly their real positions, so you can check whether important parts of your image (faces, text, key details) end up hidden behind interface chrome before you post.
Why the overlay positions differ between YouTube Shorts, TikTok, and Instagram Reels
Each platform places its caption, username, and engagement buttons in slightly different spots and with a different amount of on-screen text - mirroring each platform's actual typical layout, rather than reusing one generic overlay for all three, is what makes the comparison useful for deciding where it's safe to place key visual details on each specific platform.
Why this uses approximate mockup positions rather than a live render of the real app
These are approximate mockups based on each platform's typical layout, not pixel-exact renders of the live app - UI details change over time and can vary slightly by device and app version, so treat the overlay as a guide to the general danger zones rather than an exact, guaranteed match to what every viewer will see.
Why the bottom and right edges of the frame matter most to keep clear
Across all three platforms, captions and usernames tend to sit toward the bottom of the frame while engagement buttons (likes, comments, shares) stack along the right edge - which is exactly why those two zones are where important visual details most often get obscured, and why checking them specifically before posting catches the most common thumbnail mistakes.