How to Make a Custom Slack Emoji and Add It to Your Workspace
Step-by-step guide to preparing a custom Slack emoji: file requirements, who can upload, naming, GIF limits and how to create aliases.
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Custom emoji turn an inside joke or a recurring team phrase into a one-click reaction. This guide walks through preparing a custom Slack emoji and adding it to your workspace. The file requirements below were checked against Slack's official help page on November 3, 2026; menus and policies can change, so treat the help page as the final word.
File requirements to know first
Slack's help article says square images under 128KB with a transparent background work best. It accepts JPG, PNG and GIF files, and an animated GIF can contain up to 50 frames. The article does not fix a pixel size, but 128 by 128 pixels is the common choice, so that is what this guide assumes.
- Formats: PNG for still emoji with transparency, GIF for animation, or JPG
- Shape: square, ideally with a transparent background
- Size: under 128KB
- Animation: up to 50 frames
Create the emoji file
You do not need to draw anything by hand. Mandumon Emoji Maker turns text or a photo into an emoji, runs entirely in your browser and needs no account, so your pictures are not sent to a server.
- Open the emoji maker (link below) and choose the text emoji or image emoji tab.
- Type your text or upload an image. Images can be up to 10MB.
- Optionally pick a motion effect. You can combine up to three effects and check them in the live preview.
- Choose Slack as the save size. The output is set to 128 by 128, and for GIFs the tool reduces colors and, if needed, frames to try to fit the 128KB target. If it cannot fit, you will see a message.
- Save a PNG for a still emoji or a GIF for an animated one.
Add the emoji to your workspace
On desktop or in a web browser, the steps are short. According to the help article, adding custom emoji is not currently possible from the Android app.
- Click the smiley face icon in the message field.
- Choose Add Emoji.
- Click Upload Image and select your file.
- Type a name under "Give it a name" and click Save.
On iOS, tap the smiley face icon, enter a name, tap Add custom emoji, upload the image and tap Add. If a name is already taken you will need to pick another one.
Naming and permissions
The name is what teammates type when they search the emoji picker. Slack's article does not spell out naming rules in detail, so a short name made of lowercase letters, numbers and underscores is a safe habit, for example team_ok. In a message you type it as :team_ok: with colons, but the colons are not part of the name.
Who may add emoji depends on your workspace settings. The help article says Workspace Owners and Org Owners can restrict who can add custom emoji, so if the menu is missing, ask an admin. Owners and admins can delete any custom emoji, while regular members can delete only the ones they added.
Creating an alias
An alias gives an existing emoji a second name, so the same picture can be called :ok_team: and :good_job:. By default all members can create aliases, but guests and Frontline Members cannot.
- Click your workspace name in the top left.
- Select Customize followed by your workspace name. Owners and admins may need to open Settings and administration first.
- Choose Add Alias, then Choose Emoji, and pick the emoji from the list.
- Enter the new code under "Enter an alias" and click Save.
Check it after uploading
- View the emoji in a message and as a reaction. Small sizes blur thin text, so shorten the words or use a bolder font.
- Check both light and dark themes. With a transparent background, an outline keeps the shape readable.
- If a GIF is too large, use a single effect or start from artwork with fewer colors.
- If the Add Emoji option is missing, it is more likely a permission issue than a file problem.
For ways to make animated emoji stay readable at small sizes, see our GIF tips guide. If you also run a Discord server, the Discord specs guide covers its different limits.
