Guide
How to put your brand voice in ChatGPT custom instructions
To make ChatGPT write in your brand's voice in every chat, put a short voice guide in custom instructions: three or four "this, not that" traits, a handful of words you use and avoid, and one sentence that sounds like you. Build it from three to five texts that already sound right, not from adjectives: count your sentence length and how often you say "you", then name the traits and prove each with a line you actually wrote. Custom instructions apply to every chat and have a limit (1,500 characters on Free and Go and 5,000 on Plus and above, per OpenAI's help page read through search-result text), so the full guide with its examples belongs in a project file or a skill. If you write for several brands, give each its own project instead.
Short answer
- In custom instructions: traits, words, one sample line.
- From real texts, measured, not adjectives.
- The full guide in a project file or a skill.
- Several brands: one project each.
What goes where
| Part of the voice | Where it goes |
|---|---|
| Three or four traits, a few words to use and avoid, one sample sentence | Custom instructions, so every chat uses them |
| The full guide: every trait's do and don't, the whole word list, tone for bad news | A file in a project, read when you write longer pieces |
| Rewriting a draft in the voice | A skill, used when you ask for a rewrite |
| A second brand or a client's voice | Its own project, not your custom instructions |
The brief to copy
Voice guide brief
"Here are [3 to 5] texts that sound like us: [paste]. Measure them: average sentence length, how often they say "you" against "we", contractions, exclamation marks, how sentences open. Place them on the four tone dimensions: formal or casual, serious or funny, respectful or irreverent, matter-of-fact or enthusiastic.
Name 3 or 4 traits as "this, not that" pairs. Prove each with a line quoted from the samples and the same idea written the wrong way; drop any trait you can't quote. List 8 to 15 words we use and words we avoid.
Then write a version for my custom instructions in under [limit] characters: the traits, the habits, a few words each way, one sample sentence, and a line pointing to the full guide in my project."
A worked example
Illustration: a made-up business. The marketer at Larkspur Coffee, a small roaster, pastes the home page, a newsletter and a product card. The samples average 11 words a sentence, say "you" 14 times to "we" 4, never use an exclamation mark, and include the line "Roasted on Monday, in your grinder by Thursday." The custom instructions that come back, at 511 characters:
Custom instructions: brand voice
I write for Larkspur Coffee, a small roaster. Write in our voice: warm, not gushing; specific, not technical; confident, not pushy. Short sentences, about 11 words. Speak to "you" more than about "we". No exclamation marks. Numbers as figures.
Words we use: roast date, beans, brew, cup, you.
Words we avoid: artisanal, premium, curated, elevate, indulge.
Sounds like us: "Roasted on Monday, in your grinder by Thursday."
For anything longer than a social post, use the Brand voice file in my Marketing project.
The next product card she asks for no longer says "Elevate your mornings with our premium artisanal House Blend, roasted fresh every week!" It says "Our House Blend is roasted every week, so the bag you open is never old." Same fact, in the voice.
Next step: one voice for the whole team
Once your own instructions carry the voice, the rest of the team needs the same guide in their AI. One brand voice for a marketing team's AI writing covers sharing it so every writer works from one version.
Skills for this
- MarketingBrand voice guide and rewriteExtracts a voice guide from 3 to 5 sample texts (traits with do and don't pairs, a word list, mechanics) and rewrites a draft in it.
- AI practiceContext brief for an AI assistantWrites instructions for an AI assistant or agent: role, audience, can and can't, sources of truth, tools, format, examples, edge cases, and handoff.
- MarketingSocial posts from an articleTurns one article into a LinkedIn post, an X thread, and a short post, each hooked on the article's most specific point.
Questions
Can I put my brand voice in ChatGPT custom instructions?
Yes, a short version of it. Custom instructions apply to every chat, so three or four traits, a few words to use and avoid, and one sentence that sounds like you will shape every draft. Keep the full guide, with examples and the complete word list, in a project file or a skill, and point to it from the instructions.
What should a brand voice guide include?
Three or four traits written as "this, not that" pairs, the way Mailchimp's guide does ("smart but not snobbish"), each proved by a line quoted from your own writing; where you sit on Nielsen Norman Group's four tone dimensions; words you use and avoid; and the habits you can count, such as sentence length, "you" against "we", and exclamation marks.
Custom instructions or a project for brand voice?
One brand you always write for: custom instructions. Several brands, as at an agency: one project per brand, because custom instructions apply to every chat and would mix them. Either way, the long guide lives in a file the project reads, which keeps you inside the custom instructions limit.
AI skill
Have your AI write in your brand's voice
Put this skill in AI Skill Pod and everyone on your team gets it in their Claude, Cursor or ChatGPT (Pro, Business, Enterprise): one invite link, free to start. Brand voice guide and rewrite has your AI build the voice guide from three to five texts that sound like you: sentence habits measured from the samples, three or four "this, not that" traits each proved with a quoted line, words to use and avoid, and a rewrite of your draft that shows which trait each change serves.
14 days free · No card needed
Sources
- Nielsen Norman Group: The four dimensions of tone of voice — formal vs. casual, serious vs. funny, respectful vs. irreverent, matter-of-fact vs. enthusiastic (read 2026-11-05)
- Mailchimp Content Style Guide: Voice and tone — traits written as pairs, such as "smart but not snobbish" (read 2026-11-05)
- OpenAI Help: ChatGPT custom instructions — up to 1,500 characters on Free and Go, 5,000 on Plus, Pro, Business, Enterprise and Education; read through search-result text, the page blocks automated reads (read 2026-11-05)
- ChatGPT docs: Projects and chats — project instructions apply across the project's chats, next to its files (read 2026-11-05)