How to Write ChatGPT Custom Instructions for Your Business (With Examples)

You open ChatGPT, ask for a customer email, and spend the first two minutes typing the same background you typed yesterday. What your business does. Who you're writing to. That you don't say "valued customer."

Then tomorrow you do it again.

ChatGPT custom instructions fix that. You write your business down once, in a settings box, and ChatGPT reads it at the start of every chat from then on. It takes about twenty minutes and costs nothing.

What custom instructions actually are

Think of a short note pinned above your desk that a new assistant reads before answering anything. Custom instructions are that note, for ChatGPT.

Everything you put in there gets loaded into every conversation you start, automatically. You don't paste it. You don't remind it. It's just there.

That matters because ChatGPT starts every new chat knowing nothing about you. It's read a large chunk of the internet and none of your business. So when you ask for "an email to a customer whose order is late," it writes the average version of that email, assembled from every late-order email ever published.

Where to find them

In ChatGPT, open Settings, then Personalization, then Custom Instructions. You'll see a couple of text boxes. One asks what ChatGPT should know about you, the other asks how you want it to respond. OpenAI rearranges this screen now and then, so the labels may read a little differently by the time you get there. The two jobs stay the same.

You get roughly 1,500 characters per box. That's a few paragraphs, so you'll be choosing what matters rather than writing an essay.

Why most custom instructions don't help

Search around and you'll find people filling these boxes with adjectives. "Be professional, friendly, and engaging. Write with confidence and clarity."

That does almost nothing, and here's why. ChatGPT reads "friendly" against millions of pages that also described themselves as friendly, then hands you the average of all of them. "Professional" gets you stiff. "Engaging" gets you exclamation points.

Adjectives point at a feeling. Facts and examples give it something to work from.

So write the boxes the way you'd brief a sharp new hire on their first morning. What the business is, who walks through the door, what you sell, how you talk. Specifics, not vibes.

What to write in the first box

This one is about your business. Cover four things:

What you do, plainly. "I run a three-van landscaping company. Weekly maintenance, spring and fall cleanups, and a few design jobs a year. Residential, no commercial contracts."

Who your customers are. "Homeowners who care about the yard and don't want to spend their Saturday on it. Most found us through a neighbor. They care about showing up when we said we would."

What you actually sell. List your real services and the rough prices if you're comfortable. This is the part people skip, and it's the reason ChatGPT keeps inventing offers you don't have.

How you sound. Give it three or four concrete rules. "Short sentences. I use first names. I never say 'valued customer' or 'reach out.' A little dry humor is fine. I don't use exclamation points."

What to write in the second box

This one is about the output. Keep it short and practical:

• "Default to under 200 words unless I ask for more."
• "Skip the preamble. Start with the answer."
• "Give me one version, not three options."
• "If you need something from me to do this well, ask before writing."
• "Plain English. No marketing hype."

That last one earns its place. Left alone, ChatGPT reaches for "streamline," "leverage," and "in today's fast-paced world." Tell it not to.

A template you can fill in

Copy this, swap in your details, paste it into the first box.

I run [what the business does] in [where]. We serve [who your customers are, and what they care about].

What I sell: [your two or three real offers, with rough prices].

How I write: [three or four rules about your voice]. Words I never use: [your list].

When you write for me, assume the reader is [your customer], not another business.

And for the second box:

Keep responses under [your number] words unless I ask for more. Start with the answer, skip the wind-up. One version, not several. Plain English, no marketing language. Ask me a question if you're missing something you need.

Twenty minutes on this beats another year of pasting context into every chat.

What to keep out of the boxes

Custom instructions get stored on your ChatGPT account, so treat them like anything else you'd leave on a shared screen. Leave out customer names and contact details, order numbers, anything financial about a specific client, and anything somebody told you in confidence.

You're describing how your business sounds and what it sells. You can do all of that without a single real customer's information in there.

How to tell it's working

Ask for something you've asked for before. A follow-up email, a service description, a reply to a review. Compare it to what you got last month.

You're looking for three things. It should know what you sell without being told. It should aim at your actual customer. And it should sound closer to you, without the words you banned.

If it's still generic, the usual cause is a first box full of adjectives. Go back and add specifics: real offers, real customer, real rules about your voice.

Where custom instructions stop

They're the fastest win, and they have a ceiling. You've got 1,500 characters, which holds a summary of your business and not much of your actual writing.

When you want ChatGPT to match your rhythm and word choices rather than a description of them, you need to show it real samples of your writing. How to make ChatGPT sound like you covers that, and how to train ChatGPT on your business's voice covers the business-wide version. For the whole picture and the order to do it in, start with how to teach ChatGPT about your business.

You can also go a step further and build a Custom GPT, which holds full documents instead of a paragraph.

What you get back

Two minutes of re-explaining, every single chat, gone. Drafts that already know what you sell. Fewer rewrites, because the first version lands closer.

That's an afternoon of typing saved every month, and it compounds, because every chat after this one starts from a better place.

If writing all of this down from a blank page sounds like the hard part, that's the job Business Brain does. A guided interview pulls your voice, your customers, and your offers out of you and shapes them into a file you can paste into ChatGPT, Claude, or anything else. Same result, without the blank page.

Either way, do it once. Your next hundred chats get better.