Key Takeaways
- AI copy sounds generic because the model falls back on the most common phrasing when it has no rules or samples of your writing.
- A brand voice file is one page: reader, voice traits, words you use and avoid, sentence rules and two or three real samples.
- Load it once: Gemini Skills (replacing Gems for personal accounts on 17 November 2026), a Copilot Chat agent, or a Perplexity Space.
- Test it blind with a colleague before rollout, and keep the file short; long files get followed loosely.
A one-page voice file, loaded once into the AI tool you already use, removes most of the rewriting you do on every AI draft. You build it in under an hour and it works in every chat after that.
It matters because readers notice. In Bynder's study of 2,000 UK and US consumers, about half correctly picked out the AI-written copy, and 52% said they feel less engaged with copy they suspect is AI-generated.
Why does AI-written copy sound like AI?
Without rules or samples, a language model writes the most statistically typical version of your request. That produces the familiar tells: stacked adjectives, tidy three-item lists, the same sentence length and stock openers. A voice file replaces that average default with your own rules and real examples.
Readers rarely spot AI from one word. They spot a pattern. These are the ones that show up most in marketing drafts:
- Openers that announce instead of saying something, such as "In today's fast-paced world"
- Everything grouped in threes, with every paragraph the same length
- Abstract praise words (seamless, robust, cutting-edge) where a number or a fact should be
- No local detail: no prices in HK$, no place names, no customer language
What do you need to build a brand voice file?
You need five pieces of copy your team is proud of, a text editor, and one AI tool that can store instructions: Gemini Skills, a Microsoft 365 Copilot Chat agent or a Perplexity Space. All three are usable in Hong Kong. Budget about an hour for the first version.
You need
- Five recent pieces of on-brand copy: a post, an email, a web page, a reply to a customer, a product description
- One of the tools in the table below, signed in on desktop
- Your company policy on what may be uploaded to AI tools
| Tool | Where the voice file lives | Setting location | Usable in Hong Kong? |
|---|---|---|---|
| Gemini (personal Google account) | Skill with instructions and files | gemini.google.com > Customize > Skills > Create > Create manually | Yes, rolled out to all Hong Kong users from March 2026 |
| Gemini (Workspace account) | Gems for now; skills arrive later | Sidebar > Gems (moves to skills in March 2027) | Yes |
| Microsoft 365 Copilot Chat | Agent with instructions and uploaded files | Copilot Chat > New agent > Skip to configure | Yes; knowledge options depend on your licence |
| Perplexity | Space with custom instructions | Spaces > Create a Space > Custom Instructions | Yes; file uploads need Pro or Enterprise Pro |
| ChatGPT, Claude | Projects | Not covered here | Not officially supported in Hong Kong |
Sources: Google's skills help page and Gems transition page, Microsoft's Agent Builder knowledge guide, Perplexity's Spaces help article and Hong Kong Free Press on the Gemini rollout.
How do you write a brand voice file?
Write one page in five blocks: who you write for, three voice traits with what each does and does not mean, words you use and avoid, sentence and format rules, and two or three real samples. Concrete rules beat adjectives, so write "prices in HK$, always" instead of "be clear".
Step 1: Pull the patterns out of your best copy
Paste your five good pieces into your AI tool and ask it to describe them. This gives you a first draft of the rules in your own terms.
Here are 5 pieces of copy from [brand]. Describe the writing style as rules a new copywriter could follow: sentence length, how we open, words we repeat, words we never use, how we handle numbers and prices, how formal we are, and what we do that competitors don't. Quote examples from the text for each rule. Do not praise the copy.
[paste 5 pieces]Step 2: Fill in the template
Edit the output into this structure. Keep it to roughly one page; Google's own skill-writing advice is to keep instructions concise and include concrete examples.
BRAND VOICE: [brand name]
Use this for any marketing, social, email or web copy for [brand].
READER
[Who reads us, e.g. Hong Kong office managers, 30 to 50, read on phone between meetings.]
VOICE (3 traits)
1. [Direct]: means [lead with the answer, one idea per sentence]. Does not mean [blunt or cold].
2. [Practical]: means [every claim has a number, date or example]. Does not mean [technical jargon].
3. [Local]: means [HK$ prices, Hong Kong places, how our customers actually talk]. Does not mean [slang].
WORDS WE USE
[customers, not users] [team, not workforce] [list 5 to 10]
WORDS WE NEVER USE
[seamless, cutting-edge, unlock, elevate, game-changer, in today's world] [add yours]
RULES
- Average sentence under [18] words; mix short and long.
- Open with the result or the problem, never with background.
- No more than one list per piece. Do not group everything in threes.
- Numbers as digits. Prices as HK$[x].
- End with one clear next step, not a summary.
SAMPLES (match these)
[Sample 1: paste a short real piece]
[Sample 2: paste a short real piece]
BEFORE YOU ANSWER
Check the draft against WORDS WE NEVER USE and RULES. Fix anything that breaks them.How do you load a voice file into Gemini, Copilot and Perplexity?
Store it where the tool keeps reusable instructions. In Gemini, create a skill under Customize > Skills. In Copilot Chat, build an agent from New agent > Skip to configure. In Perplexity, paste it into a Space's Custom Instructions. Each takes about five minutes once the file is written.
Gemini Skills (personal Google account, web or Mac app)
- Go to gemini.google.com > Customize (under More if hidden) > Skills > Create > Create manually.
- Name: lowercase with hyphens, for example brand-voice.
- Description: say when Gemini should use it, for example "Use when drafting any marketing, social, email or web copy for [brand]." Gemini reads this to decide when to apply the skill automatically.
- Instructions: paste your voice file.
- Optional: Add > files to attach your sample pieces (.docx, .pdf, .md and .txt work; .doc does not). Then click Create.
- Use it by typing / (or @ on newer versions) and choosing the skill, or let Gemini apply it when the description matches.
Microsoft 365 Copilot Chat agent
- In Copilot Chat, choose New agent in the left pane, then Skip to configure.
- Fill Name, Description and Instructions; paste the voice file into Instructions.
- Under Knowledge > Upload, add your sample files (up to 20 embedded files per agent).
- Leave Only use specified sources off for writing tasks, so the agent can still draft freely.
- Test in the Try it panel, then click Create and share with your team.
Perplexity Space
- Spaces in the left menu > Create a Space > enter a Title.
- Paste the voice file into Custom Instructions.
- With Pro, add sample files through the context icon (up to 50 files per Space, 25 MB each).
How much does a brand voice file cost to run?
Usually nothing extra. Gemini Skills work without a paid Google AI subscription, Perplexity Space instructions work on the free plan, and Copilot Chat agents run inside your Microsoft 365 plan, with knowledge options set by your licence. The real cost is the hour to write it and the editing time it saves.
Each run uses the same plan you already pay for, so there is no per-draft charge. The return comes from fewer rewrite rounds. A worked example: if a voice file saves one 15-minute rewrite on each of 10 pieces a week, that is 2.5 hours a week, or roughly 10 hours a month for one marketer.
What goes wrong with brand voice files, and how do you fix it?
Most failures come from files that are too long, banned-word lists the model works around with odd synonyms, skills that never trigger because the description is vague, and samples that contradict the rules. Each has a quick fix, and none needs a new tool.
- The file is four pages long and half-followed. Cut it to one page. Microsoft's guidance on document length for Copilot makes the same point: concise files work better.
- Banned words come back as near-synonyms. Pair each banned word with what to write instead, for example "not seamless; say how many steps it takes".
- The Gemini skill never fires on its own. Rewrite the description to name the tasks ("posts, emails, product pages") rather than "brand voice".
- Files silently missing after the Gems switch. Legacy .doc, .xls and .ppt, audio, video and archives do not carry over to skills. Re-save as .docx or .pdf and upload again.
- A shared Copilot agent exposes its files. Anyone who can use the agent can get answers from its uploaded files, so never embed client lists or personal data.
How do you test a brand voice file before rolling it out?
Run a blind test. Generate three pieces with the voice file and three without, mix them with two human-written pieces, and ask a colleague to sort them. If the voice-file drafts land with the human pieces, roll it out; if not, tighten the rules that the drafts broke.
Checklist
- File is one page or less, with three traits and a does-not-mean line for each
- Every banned word has a replacement instruction
- Skill or agent description names the actual tasks
- Blind test passed with at least one colleague outside marketing
- No client names or personal data in the file or uploads
Last verified: 5 November 2026. Menu names change often; if a path above has moved, search the tool's help page for "skills", "Agent Builder" or "Spaces".
One file, every tool
The voice file is the cheapest fix for generic AI copy because you write it once and every tool reads it. Start with Gemini or Copilot, whichever your team opens first each morning, run the blind test, and copy the same file into the next tool when it passes.
Empowering AI. Centered on you.
Now check whether AI engines quote your content
Copy that sounds like you is the first half. The second is whether ChatGPT and Gemini cite your site when customers ask. Run a free AEO audit to see where you stand, and we'll walk you through every step of fixing what it finds.
Frequently Asked Questions
Will my existing Gemini Gem become a skill automatically?
Yes, for personal Google accounts. Google converts Gems to skills on 17 November 2026; Gems turn read only that day and are removed on 17 December 2026. Workspace accounts move in March 2027.
Can I use the same voice file in ChatGPT or Claude?
The file is plain text, so it works anywhere that accepts instructions. ChatGPT and Claude are not officially supported in Hong Kong, so check your company policy before using them for work.
Does a brand voice file make AI text undetectable?
No. It removes the most generic patterns and makes drafts closer to your style, but a person should still edit every piece before publishing.
Is it safe to upload past marketing copy as samples?
Published marketing copy is usually fine. Remove client names, personal data and anything confidential first, especially in a shared Copilot agent, where every user can draw on uploaded files.