Create a custom Slack emoji
Select one still image, such as an illustration, and fit it to a 128 × 128px square for a custom Slack emoji. Choose whether to keep the whole image or crop it, check the artwork and transparent areas, then save a PNG adjusted to the recommended target of under 128KB.
What you can do
Fit the image to a square PNG
Create a 128 × 128 px PNG. Choose whether to keep the whole image or crop it, and check how it looks as an emoji.
Prepare a small image as recommended
Create an image to match Slack's recommendation of a transparent image under 128 KB. The recommended file size is not treated as a mandatory limit for every image that can be registered.
How to use
Select an asset for the emoji
Select one still image, such as the illustration you want to use.
Check its appearance in the square
Check the margins and transparent areas, and switch to cropping if needed.
Save and register in Slack
Save the PNG, then name and register it through Slack's Add Custom Emoji option.
Useful when
Create images for team reactions
Fit artwork used by your team, such as confirmation or thanks, to square images.
Make a transparent asset into a small PNG
Adjust the file size as a PNG that preserves transparency without adding a white background around it.
Preparing custom emojis
The under-128 KB setting is based on a recommendation
Slack recommends small square images with transparency. This tool adjusts the output to under 128 KB.
Check registration permissions in Slack
Even if you can create the image, workspace settings may restrict who can add it.
Frequently asked questions
Is 128 KB Slack's mandatory limit?
The official guidance presents it as a recommendation. This page creates output under 128 KB to match that recommendation.
Can I also create animated emojis?
Slack supports GIFs, but this use case accepts and outputs still images only.
Can I also set name aliases?
Emoji names and aliases are settings in Slack. This page creates a PNG image.
File handling
- Input
- One still image.
- Default settings
- 128 × 128 px / Keep the whole image / PNG.
- Output
- A PNG under the recommended target of 128 KB.