Commit messages

Many open-source projects use a single emoji at the start of a commit message as a quick visual tag for the type of change — a bug fix, a new feature, a documentation update — making commit history easier to scan.

Comments and documentation

Emoji in code comments or README files can add warmth and readability, particularly in developer-facing documentation, as long as they're used consistently rather than randomly scattered.

Variable and function names

While some languages technically permit certain emoji-adjacent Unicode characters in identifiers, using emoji as variable or function names is almost universally discouraged since it hurts readability, searchability, and compatibility with tooling.

Where emoji genuinely cause problems

Emoji can behave unexpectedly in string length calculations, older database character encodings, and some log-parsing tools, since a single emoji can occupy more than one character unit depending on the encoding — worth testing before using them in anything user-facing or data-critical.