The Prompt Approach vs the Document Approach
Most people try to communicate their voice through prompts -- "write in my casual but professional tone." This works for one conversation and fails the next. You have to remember to include it, the instruction varies slightly each time, and Claude has no reference point for what your voice actually sounds like.
The document approach works differently. You write a Brand Voice document once, upload it to a Claude Project, and Claude reads it automatically in every conversation. The instruction does not need to be in the prompt because it is already in the project context.
Prompt approach: teaches Claude your voice for one conversation. Document approach: gives Claude your voice permanently. Same total effort, completely different results over time.
What Goes in a Brand Voice Document
Voice sentence: One sentence describing how your writing sounds and what it does. Concrete, not adjective-based.
Always-words: Specific phrases and terms that are distinctly yours. The vocabulary your audience recognizes as coming from you.
Never-words: The list of words and phrases that feel wrong for your brand. Often more useful than the always-words because it prevents the most common defaults.
Format rules: For each format you produce (blog, caption, email, LinkedIn), three to five sentences describing how your voice behaves in that format.
Three examples: Paste in your best content. Do not summarize -- paste the actual text. Claude learns more from real examples than any description.