Portal Community
Underlying API: Slack's reactions.* Web API methods.

add

Adds an emoji reaction to a message via reactions.add.

FieldRequiredNotes
channelYesChannel containing the message.
messageTsYesTimestamp of the target message.
emojiNameYesEmoji name without colons, e.g. thumbsup.

get

Lists the reactions on a message via reactions.get. Requires channel and messageTs.

remove

Removes an emoji reaction via reactions.remove. Requires channel, messageTs, and emojiName.