It runs on your phone — everything happens on your own device — but inspecting a grid of tiny frames is far more comfortable on a laptop or desktop.
Free · runs on your device · nothing uploaded
Drop a sprite sheet (PNG, WebP, GIF or JPEG) and press Detect grid. Auto-detect projects the alpha channel onto each axis and splits the sheet wherever a whole row or column is empty, snapping to exact cells when the frames sit on a regular pitch. Opaque sheets work too — treat the corner colour as the background — or switch to Manual and enter columns, rows, cell size, margin and spacing.
Then play it forward, in reverse or ping-pong, with onion skin and a player view anchored at the feet. Tag frame ranges (walk, idle, attack) and export frame JSON, every cell as its own PNG, or a tightly re-packed sheet — or send it on to Pixel Snap, the Slicer, Chroma & Cutout or Canvas. Everything runs on this device.
Auto-detect needs gaps: fully transparent rows and columns between frames (or background-coloured ones, with the corner-colour option on). If frames touch, switch to Manual and enter the grid, or use Fit cells to the sheet.
The frame rectangles and your named tags — as a hash keyed by frame name (the atlas layout game engines read) or as an ordered array with file names.
Space plays and pauses, the arrow keys step frames, G toggles the grid, O the onion skin, V switches between Sheet and Player views, and T tags the selected frames.