Day 19: Brand Voice Guide
The Concept
Most brands do not have a voice problem — they have a consistency problem. The tone in the CEO's LinkedIn posts, the language in the product onboarding emails, the copy on the pricing page, and the words in the social media captions were written by different people at different times with different briefs, and they have gradually drifted apart. The brand sounds like itself on its best days and like a committee on the rest of them.
A brand voice guide exists to close that gap. It is not a creative document — it is an operational one. It tells writers what to do and, more usefully, what not to do. It makes consistency achievable by people who were not present when the original voice decisions were made.
The problem is that most brands either have no guide, or have a guide so abstract it provides no practical direction. "We are human, helpful, and honest" describes every brand that has ever tried to write one. A guide that cannot be violated is not a guide — it is a mood board.
Extracting voice from what already exists
The most reliable way to define a brand voice is not to write it from scratch in a workshop. It is to analyse the copy that already exists and reverse-engineer the patterns. What sentence length do you default to? What vocabulary appears repeatedly? What editorial moves do you make when you want to reassure someone, versus when you want to persuade them? These patterns are already in your copy — they just have not been named.
AI is particularly well-suited to this analysis because it can hold many samples in mind simultaneously, identify recurring patterns across different formats, and articulate those patterns in language that is specific enough to be actionable. Human editors can do this too, but it takes weeks. AI does it in minutes, using whatever samples you provide.
The specificity test
The litmus test for any brand voice guide is whether the rules are specific enough to be violated. "Write with warmth" cannot be violated — any copy can be described as warm by the person who wrote it. "Never use passive voice in calls to action" can be violated: you either did or you did not. "Avoid financial jargon — use the word 'money' not 'liquidity'" can be enforced in an edit. Specificity is what separates a guide that changes behaviour from one that gets filed and forgotten.
The vocabulary section — the words we use and the words we avoid — is often the highest-return section of a voice guide because it is immediately actionable. A writer who knows ten words to reach for and ten to avoid has a practical filter that applies to every sentence they write.
The off-brand example as negative training data
One of the most useful inputs you can give the prompt is an example of copy that does not sound like you. The contrast between what feels right and what feels wrong is often clearer than either example alone, and AI uses that contrast to identify the specific attributes that distinguish your voice from the generic. If you have a piece of copy that a colleague wrote that made you wince, paste it in. It will sharpen the output considerably.
A living document, not a final one
A brand voice guide is not a constitution. It is a working document that should be updated when the brand changes, when a new format is added, or when the guide proves insufficient for a type of content it did not anticipate. Treat the output today as version one, not the final word. Review it every six months and update the vocabulary list as the language your audience uses evolves.
Prompt of the day
Copy this into your AI tool and replace any bracketed placeholders.
Prompt
You are a senior brand strategist and editor who specialises in codifying how organisations communicate. I am going to give you a set of copy samples from our brand — emails, website copy, social posts, or any other writing we have published. Your job is to analyse these samples and extract the underlying voice: the patterns, the vocabulary, the sentence structures, and the editorial instincts that make this brand sound like itself. Then codify it into a practical style guide a new writer could use on day one. My brand and what we do: [e.g. a fintech company helping UK small business owners manage their cash flow without needing an accountant] Our target audience and their relationship with us: [e.g. owners of businesses with 2–15 employees who are competent at running their business but find financial admin stressful and time-consuming — we are the knowledgeable friend who makes it simple] Copy samples — paste at least five pieces here, labelling each one (e.g. Website homepage, Email subject lines, Social post, Product onboarding email, About us page): [PASTE YOUR COPY SAMPLES HERE] Copy we have written that we are NOT happy with — paste any examples that feel off-brand: [PASTE OFF-BRAND EXAMPLES HERE, or write 'none available'] Analyse the samples and produce a brand voice guide with the following sections: 1. Voice in three words — three adjectives that define the voice, each followed by a one-sentence clarification of what that word means in practice for this brand. 2. Tone — explain how the tone shifts across contexts (e.g. warmer in onboarding, more direct in product UI, more authoritative in thought leadership). Two to three sentences per context. 3. Vocabulary — 10 words or phrases we use regularly and 10 we actively avoid, with a one-line reason for each. 4. Sentence patterns — describe the characteristic sentence length, structure, and rhythm this brand uses. Include two or three example sentences that exemplify the pattern. 5. What we never do — five editorial rules that distinguish us from generic brand voice. Specific and enforceable, not vague principles. 6. The litmus test — one question a writer can ask of any piece of copy to check whether it sounds like us.
Your 15-minute task
Collect five pieces of copy your brand has published — try to span at least three different formats (website, email, social, ad copy, product UI). Include at least one example you are not happy with if you have one — the contrast is as useful as the good examples. Paste them all into the prompt and run it. When you receive the guide, go straight to the 'What we never do' section. If those five rules are specific enough to be enforced, the guide is usable. If they feel generic (never use jargon, always be authentic), re-run with more copy samples.
Expected win
A practical brand voice guide — voice in three words, tonal guidance across contexts, vocabulary dos and don'ts, sentence pattern analysis, five enforceable editorial rules, and a one-question litmus test — codified from your existing copy and ready to share with any writer or agency working on your brand.
Power user tip
Once you have the guide, test it immediately with: 'Using the brand voice guide you just produced, rewrite this piece of copy so it more precisely matches our voice — and annotate each change you make, explaining which rule or pattern it applies.' Paste in your weakest piece of existing copy. The annotated rewrite becomes a worked example you can include in the guide itself.