Voice and tone guidelines
Voice and tone guidelines are the documented rules defining a brand's constant personality (voice) and how it adapts by situation (tone), so anyone, including an AI tool, can write on-brand.
Voice and tone guidelines combine two things: the voice section (the personality, vocabulary, and do/don't rules that never change) and the tone section (a matrix mapping situations like launches, apologies, and onboarding to the right mood).
Documenting both is what lets a new hire, a freelancer, or an AI tool produce on-brand copy without the founder in the room. The most useful versions are short and example-led, and they live in the tools where copy gets written.
Start from the free brand voice guidelines template or read how to write brand voice guidelines.