What are Slack’s custom emoji requirements?

Slack caps custom emoji at 128KB and recommends square images of 128×128 pixels. Animated GIFs are accepted and are subject to the same size limit as static images. Check Slack’s own help documentation if an upload is rejected at a size you expected to work, since these requirements can change.

Why does Slack reject my animated emoji?

Almost always the file size. 128KB is a tight budget for an animation, and a GIF that looks short can still carry dozens of frames. Length is usually the cause rather than image quality.

Can I upload a non-square image as a Slack emoji?

Slack will accept it and scale it, but the result is unpredictable and often unflattering. Deciding the crop yourself gives you control over what stays in frame, which is why this tool asks whether to crop to fill or fit the whole frame inside.

Will the animation still loop?

Yes. The output is encoded with infinite looping, which is how Slack displays animated emoji in messages and reactions.

Slack Emoji GIF Maker

Fits a GIF to 128×128 and under 128KB in one step.

Upload a GIF

Drop a .gif file to fit it to 128×128 and under 128KB

Slack’s two requirements, handled together

Slack checks two things when you upload a custom emoji: the file must be 128KB or smaller, and it should be square at 128×128 pixels. Handling them separately is where people get stuck — you resize to 128×128, find the file is still over 128KB, compress it, and end up re-encoding an already-quantised GIF, which compounds the color loss.

This tool does both in one pass. It resizes to the required canvas first, then reduces palette and frame rate only as far as it has to in order to clear 128KB, and stops there. A GIF that fits after a light trim gets a light trim rather than maximum compression.

Because the canvas is fixed at 128×128, dimensions are not available as a lever here. That means the one remaining cost is frame count. If the tool reports it could not reach 128KB, the clip is too long — and trimming a second off will free more budget than any settings change could.

How to make a Slack emoji GIF

Upload your GIFDrop a .gif file onto the upload area, or click to browse for one on your device.
Choose how to handle the shapeIf the GIF is not already square, pick whether to crop it to fill the 128×128 frame or fit the whole frame inside it.
Fit it to the requirementsPress the button. The GIF is resized to 128×128, then compressed only as far as needed to get under 128KB.
Download and uploadCheck the reported size against 128KB, download the GIF, and upload it through the platform's own uploader.

Other platforms

Frequently asked questions

What are Slack’s custom emoji requirements?: Slack caps custom emoji at 128KB and recommends square images of 128×128 pixels. Animated GIFs are accepted and are subject to the same size limit as static images. Check Slack’s own help documentation if an upload is rejected at a size you expected to work, since these requirements can change.
Why does Slack reject my animated emoji?: Almost always the file size. 128KB is a tight budget for an animation, and a GIF that looks short can still carry dozens of frames. Length is usually the cause rather than image quality.
Can I upload a non-square image as a Slack emoji?: Slack will accept it and scale it, but the result is unpredictable and often unflattering. Deciding the crop yourself gives you control over what stays in frame, which is why this tool asks whether to crop to fill or fit the whole frame inside.
Will the animation still loop?: Yes. The output is encoded with infinite looping, which is how Slack displays animated emoji in messages and reactions.