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Prompt Engineering for Content & Sales · Brand voice, evaluation and originality · lesson 12 of 15 · 11 min

Building a brand voice guide for AI

Why a voice guide

Without a voice guide, every prompt reinvents your tone and the output drifts towards generic AI style. A concise, AI-ready brand voice guide pasted at the top of prompts (or saved in a tool's project or custom-instructions feature) makes outputs consistent across people, platforms and months.

What to include (one page)

  1. Brand in one sentence: who you serve and how you are different.
  2. Audience snapshot: who they are, the words they use, what they care about.
  3. Personality: three to four traits, each with "this, not that". For example: Warm, not gushing. Confident, not arrogant. Playful, not silly.
  4. Language rules: British or American spelling, Arabic dialect, Urdu or Roman Urdu use, emoji policy, contractions, sentence length.
  5. Vocabulary: words and phrases you love; words you ban.
  6. Formatting habits: line breaks, lists, hashtags, sign-offs.
  7. Examples: three to five real pieces that nail the voice, labeled by type.
  8. Guardrails: claims you never make, topics you avoid, required disclosures.

Example: a compact voice guide

Brand: Chai & Charts, a personal finance creator helping young Pakistani professionals build savings without guilt. Audience: 22–35, salaried, urban, bilingual; phrases they use: "salary khatam", "side hustle", "committee". Personality: Friendly, not preachy. Honest, not alarmist. Practical, not theoretical. Language: Simple English with light Roman Urdu; short sentences; no jargon without a plain explanation; max two emojis. Love: "small wins", "boring money is good money", "here's the math". Ban: "financial freedom guaranteed", "get rich", "elevate", "unlock", "hustle harder". Guardrails: Never recommend specific stocks, funds or crypto; never promise returns; always say "not financial advice" on investment topics; disclose sponsorships with #ad and the platform's paid partnership label. Examples: [3 labeled captions]

Using it in prompts

  • Paste on top: "Follow this brand voice guide strictly: [guide]. Now: [task]."
  • Project or custom instructions: many assistants let you store instructions for a project so you do not have to paste every time. Check what data the feature stores.
  • Voice check prompt: "Review this draft against our voice guide. List each place it breaks the guide, then provide a corrected version."

Building the guide with AI

You can use AI to draft the guide from your own content:

Here are 10 of my best-performing posts: [paste]. Analyze the voice: personality traits, sentence patterns, vocabulary, formatting, and what I never do. Draft a one-page brand voice guide using the structure: Brand, Audience, Personality (this, not that), Language rules, Love words, Ban words, Formatting, Guardrails.

Then edit it yourself. The model describes patterns; only you know which are intentional and which are bad habits.

Hands-on: draft, test and store your voice guide

1. Draft from your best work

Here are 10 of our best-performing pieces (posts, emails, scripts): [paste].
Analyze the voice: personality traits, sentence patterns, vocabulary, formatting, and what we never do.
Draft a one-page voice guide: Brand, Audience (with their phrases), Personality (this, not that),
Language rules, Love words, Ban words, Formatting, Guardrails (claims, topics, disclosure).
Mark anything you're unsure is intentional with [CONFIRM].

2. Blind test

Generate five pieces with the guide, mix them with five real pieces, and ask a colleague (or the client) to pick which are human-written. If they can easily spot the AI ones, note what gave them away and add it to the guide.

3. Store it where it's always applied

Put the guide in your project instructions or files (ChatGPT/Claude Projects), a Gem or custom GPT, a Copilot Notebook, or the brand hub page Notion AI reads. Claude's custom styles can also be created from writing samples, and ChatGPT's custom instructions can carry your personal voice; keep brand voices in their projects, and your personal voice in your own settings.

Before: "Friendly, authentic, innovative" at the top of a prompt, and drafts full of exclamation marks and "elevate".

After: a one-page guide with this-not-that traits, love/ban lists and three labeled examples; the blind test shows colleagues can no longer reliably spot which captions were AI-drafted after human editing.

Multiple voices

Agencies and creators with several brands should keep one guide per brand or client, clearly named, and never mix them in the same chat. Test a guide by generating five pieces and asking a colleague or the client, "Does this sound like us?"

Pitfalls

  • Adjective soup: "authentic, innovative, bold, human" means nothing without examples.
  • Guides that are too long: keep the core to about a page; the model and your team need to absorb it.
  • Set and forget: update when your positioning changes or you notice recurring edits.

Video lecture: Building a brand voice guide for AI

Lecture coming soon · 11 chapters · about 8 minutes. Read the full transcript below.

  1. Brand voice guides for AI
  2. Why a voice guide
  3. This, not that
  4. The eight sections
  5. Example 1: Chai and Charts
  6. Example 2: the agency's three voices
  7. Watch me do it
  8. Language rules for multilingual brands
  9. Using the guide
  10. Common mistakes
  11. Recap and try this now

Lecture transcript

Brand voice guides for AI

Ask five people to describe your brand voice and you'll probably hear the same words: friendly, authentic, professional, innovative. Now ask an AI to write in that voice, and you'll get something that sounds like every other brand that described itself the same way. In this lecture you'll learn to build a one page, AI ready brand voice guide that actually changes the output: personality as this not that, love and ban words, formatting rules, guardrails, and real examples. You'll see a finance creator's guide, and watch me draft one from real content, then run a blind test.

Why a voice guide

Why bother? Without a voice guide, every prompt reinvents your tone, and output drifts toward generic AI style. Different people on your team describe the voice differently, so the brand sounds like three brands. And over months, it wanders. A concise guide, stored where the AI always sees it, makes outputs consistent across people, platforms and time. And consistency is what makes a brand recognizable. When someone can tell it's you before they see the logo, that's a voice.

This, not that

Here's the most useful trick in voice guides. Describe personality as this, not that. Warm, not gushing. Confident, not arrogant. Playful, not silly. Why does that work? Because a single adjective gives the model a direction, but not a limit. Warm could mean anything up to effusive. Warm, not gushing tells it exactly where to stop. It's like tuning a radio: the adjective gets you to the right station, and the not that gets rid of the static. Three or four of these pairs capture more than a paragraph of adjectives.

The eight sections

Here's what goes on the page. The brand in one sentence: who you serve and how you're different. An audience snapshot, including the words they actually use. Personality as three or four this not that pairs. Language rules: spelling, dialect, Urdu or Roman Urdu use, emoji policy, contractions, sentence length. Love words and ban words. Formatting habits: line breaks, lists, hashtags, sign offs. Guardrails: claims you never make, topics you avoid, required disclosures. And three to five real examples, labeled by type. Keep the core to about a page. The model, and your team, need to absorb it.

Example 1: Chai and Charts

Here's a compact example. Chai and Charts is a personal finance creator helping young Pakistani professionals build savings without guilt. Audience: twenty two to thirty five, salaried, bilingual, using phrases like salary khatam and committee. Personality: friendly, not preachy. Honest, not alarmist. Practical, not theoretical. Language: simple English with light Roman Urdu, short sentences, no jargon without an explanation, maximum two emojis. Love: small wins, boring money is good money. Ban: financial freedom guaranteed, get rich, elevate, unlock. Guardrails: never recommend specific stocks or crypto, never promise returns, say not financial advice on investment topics, and disclose sponsorships. Every line changes what the AI writes.

Example 2: the agency's three voices

Now an agency scenario, with illustrative details. A social agency in Leeds manages three brands: a craft brewery, a children's dentist and a law firm. Three very different voices. Early on, a caption for the dentist came out sounding suspiciously like the brewery. The fix: one voice guide per client, each stored in its own project, and a rule that no chat ever mixes clients. Then they run a blind test with each client: five AI drafted and human edited captions mixed with five older human ones. The dentist's practice manager can't reliably tell them apart. The law firm spots two, because they're too casual, so the agency adds two ban words and a formality rule to that guide.

Watch me do it

Let me draft one. I paste ten of a plant shop's best performing posts and the prompt from the lesson text: analyze the voice and draft a one page guide, marking anything you're unsure is intentional with confirm. The draft is surprisingly good. It notices the shop always names the plant's personality, like a dramatic fern, and never uses exclamation marks. It has three confirm tags. One says: frequently uses the phrase plant parent. Is that intentional? The owner says no, she's tired of it, so it moves to the ban list. That's why you edit the guide yourself: the model describes patterns, but only you know which are deliberate and which are habits. Then the blind test. Five new drafts, five real posts, mixed. Her assistant spots one AI draft, because it's too long. I add a length rule.

Language rules for multilingual brands

If your brand works across languages, the language rules section deserves extra care, because it's where AI drifts most. Be explicit. American or British spelling. Which Arabic: Modern Standard for formal announcements, or Gulf dialect for social captions? Is Roman Urdu welcome, and how much: one phrase per caption, or whole sentences? When do you code switch, and when not? For example, English for product names and technical terms, Urdu for warmth and humor. Include one short example of each done well. And add a rule that any published non English content is reviewed by a native speaker who knows the market, because a model can produce grammatically correct text that still sounds like a translation.

Using the guide

How do you use the guide day to day? Store it where it's always applied: project instructions or files in ChatGPT or Claude, a Gem or custom GPT, a Copilot Notebook, or the Notion page Notion AI reads. Claude also lets you create custom styles from writing samples. Keep brand voices in their projects, and your personal voice in your own settings. And use a voice check prompt on anything important: review this draft against our voice guide, list each place it breaks the guide, then give a corrected version. It's a fast second pass before a human edit.

Common mistakes

The common mistakes. Adjective soup: authentic, innovative, bold, human means nothing without this not that pairs and examples. Guides that are too long: keep the core to a page. Set and forget: update the guide when positioning changes, or when you notice the same edit recurring. And mixing voices: one guide per brand or client, and never two clients in the same chat. A great voice guide is short, specific, tested, and alive.

Recap and try this now

Let's recap. An AI ready voice guide fits on one page: brand, audience and their phrases, personality as this not that, language rules, love and ban words, formatting, guardrails and real examples. Draft it with AI from your best work, then edit it yourself, confirming which patterns are intentional. Blind test it, and store it in the project, GPT or Gem where it's always applied. Here's your try this now. Paste ten of your best pieces into the draft prompt from the lesson text, edit the result, and run the blind test with one colleague. Add whatever gave the AI drafts away.

Key takeaways

  • An AI-ready voice guide fits on one page: brand, audience phrases, this-not-that personality, language rules, love/ban words, formatting, guardrails, examples.
  • Use AI to draft the guide from your best work, then edit it yourself; mark uncertain patterns to confirm.
  • Test the guide with a blind comparison and add what gave the AI drafts away.
  • Store brand voices in their own projects, GPTs or Gems; never mix clients' voices in one chat.

Try it

Use the prompt in this lesson to draft a voice guide from ten of your posts, edit it to one page, and test it on five new pieces.