How to Add Custom Emoji to Slack on Desktop and iPhone

You can add a custom Slack emoji from a computer or an iPhone. Prepare one image, choose a clear name, and save it in the correct workspace. This guide includes a real animated cat file so you can follow the upload steps without making artwork first.

Download a file with known dimensions and size

Our worked example uses MakeEmoji's sample Cat Jam animation. This smaller export is 80 × 80 pixels, 116,744 bytes, and 41 frames. It has a transparent background and repeats continuously. The animation runs for 6.84 seconds before it repeats.

Download the Cat Jam example GIF. Save it as a GIF file. A screenshot would preserve one still frame and lose the motion. For a static alternative, use the sample cat PNG: 100 × 100 pixels and 20,902 bytes.

Slack recommends square images with transparency and a file size below 128 KB. Its supported formats are JPG, PNG, and GIF; GIFs can contain up to 50 frames. See Slack's custom emoji instructions. Our sample is below both the recommended byte size and the frame limit. File checks do not replace the upload check in your workspace.

Add the emoji from Slack on a computer

1. Open the emoji picker beside the message field.
2. Select Add Emoji, then Upload Image.
3. Choose the downloaded GIF.
4. Enter cat_jam_demo in the name field and select Save.

Check the active workspace before you save. Use the sample name only if it is available. A descriptive name helps colleagues find the reaction later; a filename such as image_final_3 does not explain what the emoji means.

Add a custom emoji from an iPhone

1. Open the emoji menu beside the message field.
2. Enter an unused emoji name, then tap Add custom emoji.
3. Choose an image option and follow the upload prompts.
4. Tap Add in the upper-right corner.

These computer and iPhone steps follow Slack's current guide. It states that uploads from the Android app are not supported. On Android, move the saved file to a computer and use the computer steps above.

Complete the Cat Jam example

After the upload, search the emoji picker for cat_jam_demo. Add it to a short message in a suitable channel. Next, add it as a reaction to a message. Confirm that the face stays visible through the loop and that the small reaction is easy to recognize.

Try it beside text, rather than only in an empty message. This shows whether the cat is large enough to read during a normal conversation. Check the outline on your usual Slack theme. A thin pale border may look different on a dark background.

We measured the example's encoded file and decoded its frames. The smaller GIF was prepared with FFmpeg for our GIF compression guide. It is an actual download, not a record of an upload to a Slack workspace. Use the checks above to finish the example in your own workspace.

Prepare your own photo or animation

Choose a source with one clear subject. Crop close enough to see the expression, but leave room for ears, hands, or movement. Avoid text that needs a large preview to read. A simple face usually survives reduction better than a full screenshot.

1. Open the Slack emoji resizer and select Browse image.
2. Choose your PNG or GIF. The tool reads the image and animation metadata.
3. Select Make Slack-ready file and wait for the result.
4. Check the output preview, dimensions, byte size, and animation information.
5. Download the result and choose that file in Slack.

The resizer starts with an output target of up to 128 × 128 pixels. It can reduce dimensions, colors, or frames to fit its Slack settings. The final values depend on the source. Our 80-pixel sample is one measured export, not a promise that every animation will use those dimensions or have the same file size.

If Add Emoji is missing

Slack allows members to create emoji by default, but excludes guests. Workspace and organization owners can restrict this permission. Ask an owner to check Add and edit custom emoji. Slack documents the plan-specific controls in its custom emoji permissions guide.

Include the workspace name, your device, and the missing control in your request. If the upload control exists but the file fails, send the exact error and the saved file's size instead. That separates a permission problem from a file problem and avoids unnecessary edits.

Slack documentation and example file measurements reviewed September 20, 2026.