Someone hands you a 12 MB animation and a form that will accept 2 MB. The instinct is to look for a compression setting, and the reason none of them helps much is worth thirty seconds of explanation — it decides which of the remaining options is the right one.
How to get a GIF under 100 KB
Cut frames, then colours, then size
Halve the frame rate, reduce the palette, and shrink the dimensions — in that order, because each one multiplies against the others. For anything longer than a couple of seconds, converting it to video is the only reliable way there.
Every frame is a whole picture
This is the entire explanation, and everything else follows from it.
A video codec looks at frame two, notices that it is almost identical to frame one, and stores the difference. On a screen recording where only a cursor moves, that difference is a few hundred bytes. Thirty frames of a still background cost barely more than one.
A GIF has no such idea. Each frame is compressed by itself, with a method published in 1987, and the file is those results in sequence. Five seconds at twenty-four frames a second is a hundred and twenty independent images, and the fact that a hundred and nineteen of them show mostly the same wall is information the format cannot use.
The gap this produces is not marginal. The same clip as video routinely comes out ten to a hundred times smaller — a common example is a screen recording of a few seconds weighing several megabytes as a GIF and a couple of hundred kilobytes as video. No setting inside the format closes that.
The 256-colour ceiling, and how to use it
A GIF stores a list of at most 256 colours and then records each pixel as a position in that list. That ceiling is why photographs look dithered and gradients look striped in a GIF, and it is also the one lever the format gives you.
Cutting the palette to 64 or 32 colours makes the stream of indices far more repetitive, and repetition is exactly what the compressor rewards. On flat graphics, screen recordings and line animation the saving is large and the damage is invisible. On anything photographic it bands, and banding is the visible edge of that ceiling rather than a fault in the encoder.
The three levers, in the order that pays
Frames. Halve the rate and watch it once. Most captures run at far more frames a second than their content needs, and removing every second frame removes close to half the file. Ten a second is comfortable for a screen recording; below fifteen, real motion begins to stutter.
Colours. Then reduce the palette, for the reason above.
Dimensions. Then make it smaller on screen. This one is multiplicative and often forgotten: halving the width and the height removes three quarters of the pixels in every frame at once, which beats any per-frame setting.
Trimming the clip is the fourth and largest lever when it is available at all. Two seconds of a five-second loop is two fifths of the file, and most GIFs that people are trying to shrink contain a second of nothing at each end.
What this site can and cannot do with one
Worth saying plainly, because the tools accept a GIF and the result will surprise you otherwise.
The image tools here read your file through the browser’s own decoder, and what comes back is one still picture — the first frame. So compressing a GIF to a target size here gives you a still image under that size, not a smaller animation, and converting one gives you a single frame in the new format. Nothing here writes an animated file.
That is exactly right when a still is what you needed — pulling one frame out to use as a thumbnail or a preview is a real job and this does it in one step. When the movement is the point, it is the wrong tool, and the honest advice is a video encoder rather than an image one.
When a GIF should stay a GIF
The format survives on compatibility rather than merit. It pastes into a chat window, an old forum, an email signature and a document, and it plays by itself without a control bar or a click. That is a real advantage and it is the only one left.
So: keep it a GIF when it is going somewhere that will not take a video, and make it as short and as small as that destination allows. Everywhere else — a web page, a presentation, anything you control — the format is a habit rather than a decision, and leaving it is the saving that dwarfs all the others.
The short version
A GIF is large because it stores whole frames and cannot look between them. Cut the frame count, then the palette, then the dimensions, and trim the clip if you can. If the destination accepts video, that single change beats everything else combined — and if it does not, accept that a long animation may not fit under a small limit at all.