Social
The exact pixel sizes every platform wants, and a preview of how the post will land.
Size and framing, and not one tool here about editing the picture itself. That distinction is why these are gathered on their own: what ruins a post is almost never image quality, it is the platform cropping the top off the thing you spent an hour on.
A size to work to, or a preview to check against
The size references — Instagram post and story, YouTube thumbnail and banner, Facebook cover and post, and the single sheet covering every platform at once — give the pixel dimensions, the aspect ratio and the safe area each surface actually shows. The safe area is the number that matters. A YouTube banner is displayed at several different sizes depending on the device, and only the middle strip of it survives all of them.
The previews work the other way round. Drop in what you have made and see it inside the frame it will be seen in: the social share preview renders the Open Graph card the way Facebook, LinkedIn, X and Slack will build it, and the mockups place an image into an Instagram or YouTube layout so you can judge the crop before posting rather than after. Pair the share preview with the meta tag generator under SEO & web, which is where the tags it reads get written. Resizing the file itself is Image.