In my commit message headers, I generally like to follow the Angular contributor guidelines by prefacing my commit summaries with one of the following:

• build: Changes that affect the build system or external dependencies used
• feat: A new feature
• fix: A bug fix
• refactor: A code change that neither fixes a bug nor adds a feature
• style: Code changes that do not affect the meaning of the code, often involving whitespace
• test: Adding missing tests or correcting existing tests