Frame height defaults to image height ÷ rows — edit it if the sheet has padding.
Columns and frame width are linked (image width ÷ columns) — set whichever you know.
Playback
Order plays left→right, then wraps down to the next row. Leave end at 0 to use every frame.
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Load a sprite sheet to preview the animation
Sheet & grid ruler
Grid
Choose how many rows and columns the sheet needs, and the pixel size of each cell. Changing any of these rebuilds the grid.
Paste & edit
Click a cell to select it, then paste an image (Ctrl+V or ⌘+V). Drag inside a cell to move its image, scroll or use the − / + buttons to resize, and use arrow keys to nudge (hold Shift for bigger steps). Backspace clears the selected cell.