Slack supports both regular Unicode character entries for emoji, as well as short emoji codes which are converted into an emoji image when posted.
Users of iOS and macOS see Apple emoji design in Slack. All other platforms display emojis in Slack using designs from Google's Noto Color Emoji. This includes users on Windows, Linux, and Android.
A feature permitting choice of emoji design was discontinued in February 2018.
Emoji Short Codes
Slack permits a set of :shortcodes: to enter emojis on the platform. Typing an emoji short code such as :sparkles: inserts the ✨ Sparkles emoji.
This is stored in plain text, so copying-and-pasting a block of text which includes emojis added via shortcode will display the :shortcode: instead of the emoji character. Emoji shortcodes on Slack are derived from this repository, and do not necessarily match the same codes used on platforms such as Github.
More about Emoji Shortcodes.
In addition to regular emoji use, reactions are also available. This allows any emoji to be chosen as a response to a message. Reactions are tallied if multiple users apply the same emojis.
Slack Emoticon Codes
The following codes convert emoticons into emoji images on Slack.
Remote Work Emoji Set
A custom set of remote work emojis from Jen Lewis is available for Slack as of June 2020.
“The images range from socially distanced high fives to heads-down work and family time. There’s even one about your cat’s love for your keyboard.”