One editor, not nine separate tools
The features listed above are pages, not products. There is a single editor underneath all of them, and each page describes the part of it you came looking for. That matters because sprite work is rarely one operation. A typical job is: unpack an old sheet, drop the frames that are duplicates, fix two pixels on one pose, recolor the set for a second enemy variant, play the loop until the timing reads right, then export twice, once as an atlas for the engine and once as a GIF for the devlog post.
Run that through separate web tools and every step is a download and a reupload, with a chance to lose alignment at each handoff. Here the frames stay loaded, the layout stays put, and the step you are on is a panel away from the last one.
Why it all happens in the browser tab
Every operation, from GIF decoding to bin packing to GIF encoding, runs as code in the page rather than on a server. The practical effects are worth spelling out. Your art never leaves the machine, so there is no upload to wait for, no queue to sit in, and nothing to delete off somebody elses disk afterwards. Unfinished work in progress on an unannounced game stays as private as the folder it came from.
It also means there are no quotas. File size limits on hosted converters exist because bandwidth and storage cost money. With no transfer involved, the ceiling is your own memory, and a few hundred frames is unremarkable on an ordinary laptop.
The tradeoff is honest: a very large batch will make your fan spin, because the work is happening on your CPU instead of a rented one. That is the price of the sheet never being copied anywhere.
Who this is built for
Solo developers and small teams, mostly. If you are shipping a 2D game and the art pipeline is you, an asset pack, and whatever your engine will import, this covers the part between the two. Game jam projects get the most out of it, because a jam gives you no time to install a packer, learn its command line, and debug an atlas format at two in the morning.
It also fits people who are not primarily game developers. Web developers building a CSS sprite for icon states, modders assembling a Sparrow XML sheet for a rhythm game, teachers walking a class through frame animation, and artists who want a run cycle as a GIF to post rather than as a folder to explain.
What it is not is a replacement for a dedicated pixel art program on a long project. Aseprite and its peers do things a browser tool should not pretend to. The overlap is deliberate and narrow: the frame level fixes you want to make without leaving the sheet.
Free, and what pays for it
Every feature is available without an account, without a trial clock, and without a paid tier holding the export formats hostage. The running costs are covered by advertising on the content pages, which is why you will see ad slots on a page like this one and none at all inside the editor, where they would get in the way of the work.
An optional account exists for one thing: saving projects to the cloud so a sheet can be picked up on another machine. Skip it and nothing is missing except that convenience, since local project files do the same job and never touch a server.
Where to start
If you have loose frames and want a sheet, start with PNG to Sprite Sheet. If you have a sheet and want the frames, start with the splitter. If you have a GIF, the GIF converter turns it into frames in one drop. If you already have a sheet that works and only need a different file for your engine, the export page lists what each target reads and which menu entry writes it.
For the longer explanations, the guides go deeper than a feature page can: sheet fundamentals, packing and padding, pixel perfect scaling, palette work, and engine specific import walkthroughs. The editor itself needs no reading. Drag something onto it and it will do something sensible.