Make a custom emoji people can read in a message
The file is the easy part: a 128-pixel square PNG never goes over Slack's or Teams' size guidance. What actually sinks a custom emoji is that nobody can tell what it is once it's sitting next to a message, and a dark theme makes that worse. That's why the maker shows it small, twice, on a light and a dark theme. Judge it there.
Keep it to one shape or one short word
Text gets as big as the square allows, so fewer letters means bigger letters. In the maker, "lgtm" (short for "looks good to me") fills the square in 53-pixel type. Spell out "looks good to me" and it has to shrink to 22-pixel type to fit, less than half the size. Here's what that does at message size:
lgtm
Merged the fix 
4 looks good to me
Merged the fix 
4 For a picture, zoom in until the face or logo touches the edges. Empty space around the subject is wasted pixels.
Check the color against both themes
Dark text on a transparent background vanishes into a dark theme, and white text vanishes into a light one. If your emoji is text, give it a colored background, or pick a text color that holds up on both rows. The default here, white on Dash blue, reads on both.
Get rid of the white box behind a logo
Logos and screenshots usually come with a white rectangle behind them. On a light theme you won't notice. On a dark theme it's a white tile with your logo inside. Tick "Remove white background" and the maker clears the white around the shape, edge included, so there's no pale halo left behind. White inside the shape, like the white of an eye, stays.
Before
New logo is live 
2 After "Remove white background"
New logo is live 
2 How to add a custom emoji in Slack
- On desktop, click the smiley face icon in the message field.
- Click Add Emoji, then Upload Image, and pick the PNG you downloaded.
- Under Give it a name, type a short name, like
on-it, then click Save.
On iPhone or iPad, tap the smiley face, enter a name, tap Add custom emoji, upload the image and tap Add. Slack's Android app can't add custom emoji yet. If you don't see Add Emoji at all, your workspace owner has limited who can add them, so ask an owner or admin.
How to add a custom emoji in Microsoft Teams
- Select Emoji, GIFs and Stickers on the right of the message box, then choose Emoji.
- At the bottom, select Your org's emoji.
- On the left, select Add emoji, choose the PNG and give it a name.
- Select Add emoji to save it.
You can also add one while reacting to a message, from More reactions and then Your org's emoji. Teams admins can limit who creates custom emoji, so if the button is missing, ask your admin.
Slack vs Teams custom emoji rules
| Slack | Microsoft Teams | |
|---|---|---|
| File types | JPG, PNG or GIF | JPEG, PNG or GIF |
| File size | Under 128 KB works best | Pick files under 256 KB; Teams compresses images |
| Shape | Square, with a transparent background, works best | Square recommended |
| Animated GIFs | Up to 50 frames | GIF files accepted |
| Who can use them | Everyone in your organization; people in Slack Connect channels can add yours to their own organization | Everyone in your organization, including external people in shared channels |
Sources: Slack Help Center and Microsoft Support, both read October 12, 2026.
How this emoji maker works
The maker draws onto a 128 × 128 canvas in your browser and saves it as a PNG. A picture is cropped to fill the square from its center, and the zoom and drag move that crop. Text is sized to fill 90% of the square, on one line or two, whichever gives bigger letters. An animated GIF becomes a still image of its first frame.
A 128 × 128 image with transparency holds 65,536 bytes of pixel data (128 × 128 × 4). Even a picture that PNG can't compress at all comes out at about 64 KB, half of Slack's 128 KB. The emoji in our tests came out between 1 and 8 KB.
"Remove white background" clears the near-white pixels connected to the edges of the picture. For the pixels along that border, it takes the color of the solid shape right next to them and turns the white part into transparency. Our first version worked out the color from each edge pixel alone and left a faint dark ring around the shape, so now it borrows the color from its solid neighbor. Nothing leaves your device: there's no upload, no account and no server.
Dash lives in the same channels
That new emoji will end up on someone's weekly report or a "done" message. Dash is an AI teammate for Slack and Microsoft Teams that pulls those reports together, drafts the follow-ups and checks with you before anything goes out.