Grid34Sync helps you see how your Instagram profile will look before you post. You can drag and reorder images, check the taller 3:4 grid format and avoid important details being cropped out of view.
It can also split images into carousel slides or nine-tile grids. Files are handled locally in your browser, and you do not need an account or have to deal with watermarks, which makes it quick to use for planning a tidy feed.