I have been building a small set of free sprite tools and I would like feedback from people who actually ship OpenGameArt assets, because the workflow this solves is the one I kept hitting with LPC-style art.

The tools are at https://spritesheetbuilder.com/ and they run entirely in the browser:

• Pack a folder of PNG frames into one transparent sheet (grid or auto-pack, with padding and spacing, plus a live preview at 1–30 FPS before exporting).
• Split an existing sheet back into individual frames by grid, or by detecting the non-transparent regions when the sprites are separated on a transparent background.
• Convert an animated GIF into a sheet, and a sheet back into a GIF.

The exports are the part that matters for LPC: you get PNG plus atlas metadata, so a strip of walk frames can go into a sheet and back out as individual PNGs without any colour or alpha changes. Padding and spacing are there specifically to keep neighbouring frames from bleeding into each other when the engine filters the texture.

Two honest limitations: the sheet is capped at 4096×4096 and 200 frames, and transparent-region detection is not a substitute for real atlas coordinates when sprites overlap or are unevenly spaced — use the grid for those.

Nothing is uploaded; decoding, packing and export all happen on the visitor's machine, which is also why I did not want to build it as a server-side service.

The splitter is at https://spritesheetbuilder.com/sprite-sheet-splitter if you want to try it on something you already have. I am happy to take requests for formats that your engine needs.