Guide: ChatGPT
Make ChatGPT write in your brand voice
ChatGPT has several places to keep instructions, each with its own size limit. Here is where a brand voice belongs, how much fits, and what to write so the voice actually holds.
Updated
Where the instructions go
| Place | Best for | Room |
|---|---|---|
| Custom instructions (Settings, Personalization) | One brand, every chat | 1,500 characters on Free; up to 5,000 on paid plans |
| A Project's instructions | Several brands or clients, one Project each | Its own instructions box, per Project |
| Skills (where your plan has them) | Teams on Business, Enterprise and Edu plans | The full SKILL.md |
OpenAI raised the custom instructions limit for paid plans to 5,000 characters in July 2026; the Free plan has 1,500. Limits change, so if ChatGPT cuts your text off, use the shorter version.
If you write for more than one brand, use Projects: one Project per brand, with that brand's voice in the Project instructions. Putting a single brand in your personal custom instructions will colour everything you write, including unrelated chats.
What to write in 1,500 characters
A short box forces choices. Spend it on what ChatGPT gets wrong by default: its own habits. Left alone it reaches for exclamation marks, triplets of adjectives and words like “elevate”. Tell it what you do instead, with numbers where you can:
Write everything for Acme in Acme's brand voice.
Plain and direct, like a founder explaining a tool to a peer.
Voice:
- Confident, never loud: state the outcome first, then how.
- Specific over sensory: name the number, the place, the person.
Style:
- Median sentence: 11 words. Short ones for emphasis.
- No exclamation marks. No emoji.
- Headings in sentence case.
Use: small batches, named farms, roast date.
Write exactly: Acme Roast Club.
Avoid: artisanal, curated, elevate.
Never invent facts, numbers or claims about Acme; ask for them.That example is about 540 characters, so there is room for a few more of your own rules or words.
What to add when you have 5,000
- The full set of voice traits, each with what to do and what to avoid.
- Rules for headlines and calls to action, with real examples from your site.
- Brand facts the model may use, so it stops inventing customer names and numbers.
- Two or three real passages that show the rhythm you want.
- A short checklist ChatGPT should run before it hands you the copy.
Why the voice drifts, and what helps
- Generic instructions. “Friendly and professional” describes ChatGPT's default, so nothing changes. Specific, checkable rules do.
- Long conversations. Instructions carry less weight deep into a long chat. Start a new chat for each new piece of copy.
- No examples. Rules describe the voice; examples show it. Even two real lines help.
- No review step. Ask: “Check this draft against my brand voice instructions and fix anything that breaks them.” It catches most slips.
Get both versions without writing them
Saylike reads your website and writing samples and gives you a short version that fits 1,500 characters and a full version under 5,000, both built from the same analysis as the Claude skill. Every quote in them was checked against your own writing. For the Claude side, see making Claude write in your brand voice.