YouTube Thumbnail Checker
A thumbnail that looks great full screen can be unreadable at the size people scroll past it. Preview yours at real sizes next to a title, check it in black and white, and check YouTube's limits. The image stays in your browser.
What makes a thumbnail readable small
Three words or fewer, big and bold; one face or object, not five; strong contrast between text and background. If it still reads in black and white at the smallest size, it works. Don't repeat the title: the thumbnail and title should say different things.
Need it at 1280×720? Use the image resizer, or grab a frame from your video with the frame grabber.