Tone indicators are shorthand for words used to convey tone, which the Cambridge Dictionary defines as "a quality in the voice that expresses the speaker's feelings or thoughts".

The tone of someone's voice can be joking, or serious; it can be teasing, or threatening. It can be negative, positive, or neutral. It can be sexually suggestive, or entirely friendly. Tone can do so much to change the meaning and implications of a sentence.

Tone tags/indicators are short text at the end of a message to let the reader know how the message is meant to be read, clear up any misunderstanding, or simply tell what the tone is. The tag is separated from the message it is indicating by a slash (/).

Tone tags are especially useful for neurodivergent folk, as they can have a harder time understanding and reading tone through text, as apposed to someone who is neurotypical and may have an easier time.