How to build a custom GPT for your business (step-by-step)

I built my first custom GPT on a whim. I was tired of pasting the same instructions into ChatGPT every single time I wanted to write social media posts for the business. So I thought: there must be a better way.

There was. Ten minutes later I had a custom GPT that already knew our brand voice, our audience, and exactly how we like our posts structured. No more copy-pasting. No more re-explaining everything from scratch.

Since then I have built over 10 custom GPTs. Some for our Smash Your AI bundle, some for clients, and some just for myself. They are one of the most useful features in ChatGPT, and most people have no idea they exist.

Let me show you how to build one from scratch.

What is a custom GPT?

A custom GPT is your own version of ChatGPT that is pre-loaded with specific instructions, knowledge, and personality. Think of it like a specialist assistant that already knows exactly what you need.

Instead of starting every conversation with "You are a marketing expert who writes in a casual tone for UK small businesses..." you set that up once. Then every time you open that GPT, it already knows all of that. You just type your request and go.

Here is a simple way to think about it:

• Normal ChatGPT = a blank canvas. You have to explain everything every time.
• Custom GPT = a trained team member. They already know the brief.

You can create custom GPTs for anything. Writing emails, generating ideas, answering customer questions, drafting proposals, creating content. If you find yourself repeating the same instructions, a custom GPT will save you a lot of time.

Why custom GPTs are a game-changer for businesses

Here is the problem I kept running into. Every time I opened ChatGPT, I had to set the scene. Explain the context. Describe the tone. List the rules. It took ages, and half the time I forgot something important.

Custom GPTs fix this completely. You do the setup once, and then it just works. Every single time.

But there is a bigger reason they matter for businesses. They make AI consistent. When your whole team is using the same custom GPT, everyone gets results in the same brand voice, following the same rules, hitting the same quality standard.

No more one person getting great results because they are good at prompting, while another gets rubbish because they typed "write me a blog post" and hoped for the best.

The businesses I have seen get the most out of AI are the ones that build custom GPTs for their most common tasks. It is the difference between giving your team a blank notebook and giving them a pre-filled template.

What you need before you start

One quick thing before we dive in. To create custom GPTs, you need ChatGPT Plus. That costs $20 per month (about 16 pounds). The free version of ChatGPT does not let you build them.

If you are wondering whether Plus is worth paying for, I wrote about that in our guide to paid AI plans. Short answer: if you use AI for work, yes.

You do not need any coding skills. You do not need any technical knowledge. If you can write a clear set of instructions, you can build a custom GPT.

Step-by-step: building your first custom GPT

Let me walk you through building a real one. We are going to create a custom GPT that writes social media posts for a small business. You can swap the details for your own business as you follow along.

Step 1: Open the GPT builder

In ChatGPT, click "Explore GPTs" in the left sidebar. Then click "Create" in the top right corner. This opens the GPT builder, which has two tabs: Create and Configure.

The "Create" tab lets you build a GPT by chatting with ChatGPT. That sounds nice, but honestly I skip it every time. The "Configure" tab gives you much more control. Click Configure.

Step 2: Give it a name and description

Keep the name short and clear. You will see it in your sidebar, so make it obvious what it does.

• Name: "Social Media Writer"
• Description: "Writes social media posts for [Your Business Name] in our brand voice."

That is it. Do not overthink this part.

Step 3: Write your instructions

This is the most important part. The instructions box is where you tell the GPT who it is, how it should behave, and what rules to follow. This is what separates a useful custom GPT from a useless one.

Here is what bad instructions look like versus good ones:

This tells the GPT almost nothing. What business? What tone? What platform? What length? It will guess, and the results will be generic.

See the difference? The good version gives the GPT a clear identity, a specific audience, detailed rules, and a process to follow. It will produce dramatically better results from the very first message.

Step 4: Add conversation starters

Conversation starters are the buttons that appear when someone opens your GPT. They give users a quick way to get started instead of staring at a blank screen.

Good examples for our social media writer:

• "Write a post about our new sourdough loaf"
• "Create a weekend special announcement"
• "Write a behind-the-scenes post about our baking process"
• "Draft a post for a bank holiday opening hours update"

These also act as examples of what the GPT can do. They help anyone on your team who picks it up for the first time.

Step 5: Upload knowledge files (optional but powerful)

This is where custom GPTs get really clever. You can upload files that the GPT can reference when answering. Things like:

• Your brand guidelines document
• A list of your products or services
• Examples of posts you have written before
• Your tone of voice guide
• FAQs or common customer questions

For our bakery example, you might upload a menu PDF and a document with 10 past social media posts you liked. The GPT will use these as reference material. It will not memorise them word for word, but it will pull from them when relevant.

I upload knowledge files to almost every custom GPT I build. It makes them so much smarter.

Step 6: Save and test

Click Save in the top right. You will get three sharing options:

• Only me - just you can use it
• Anyone with a link - you can share the link with your team
• Public - anyone can find it in the GPT store

For business use, "Anyone with a link" is usually the best option. Your team can use it, but random strangers cannot find it.

Now test it. Open the GPT and try a few different requests. See if the tone is right, the length is right, and the rules are being followed. If something is off, go back to Configure and tweak the instructions. It usually takes me two or three rounds of tweaking to get it spot on.

Tips for writing great GPT instructions

I have written instructions for over 10 custom GPTs now. Here is what I have learned works best:

• Be specific about what you do not want. "Never use corporate jargon" is more useful than "write naturally." Telling the GPT what to avoid is just as powerful as telling it what to do.
• Include your audience. "Write for busy small business owners who have no technical background" changes the output completely.
• Set a default length. Without one, the GPT will waffle. "Keep responses under 200 words unless asked for more" works well.
• Tell it to ask questions. Adding "If my request is vague, ask clarifying questions before writing" stops the GPT from guessing and getting it wrong.
• Use plain language. You do not need fancy prompt engineering syntax. Write your instructions like you would brief a new team member.
• Test with edge cases. Try requests that are slightly outside what you designed it for. See how it handles them. Adjust the instructions if needed.

5 custom GPT ideas by business type

Not sure what to build? Here are five ideas based on the types of businesses I have worked with. Every single one of these would save real time.

The pattern is the same every time. Find a task you repeat often, write clear instructions for how you want it done, and let the GPT handle it.

How to share custom GPTs with your team

Once you have built a GPT that works well, you will probably want your team to use it too. Here is how sharing works:

1. Open the GPT and click the pencil icon to edit it.
2. Click Save and choose "Anyone with a link".
3. Copy the link and send it to your team.

Anyone with ChatGPT Plus can use it. They just click the link and the GPT appears in their sidebar.

One thing to note: your team members each need their own ChatGPT Plus subscription. The GPT itself is free to share, but they need Plus to access it.

This is exactly what I did when building GPTs for clients. I set them up, tested them, then sent the link over. The client did not need to understand how to build one. They just used it.

Common mistakes when building custom GPTs

I have made all of these so you do not have to:

• Instructions that are too short. "Be helpful and write good content" is not enough. The more detail you give, the better the results. My best-performing GPTs have 300-500 words of instructions.
• Not testing enough. Build it, test it with 5-10 different requests, tweak the instructions, test again. The first version is never perfect.
• Forgetting to say what to avoid. If you do not tell it "never use bullet points" or "never start with a question," it will do those things when it feels like it.
• Uploading too many knowledge files. Stick to the most important ones. If you upload 20 documents, the GPT can get confused about which to reference. Three to five focused files is the sweet spot.

Or skip the building entirely

If this all sounds useful but you do not fancy building them yourself, we have done the work for you.

Our Smash Your AI bundle includes 10 pre-built custom GPTs covering the tasks businesses use most. Social media content, email writing, meeting summaries, blog posts, and more. Each one comes with detailed instructions already written and tested.

You just open them up and start using them. No setup. No instructions to write. They are ready to go straight out of the box.

The bundle also includes 168 prompts, 2 workbooks, 6 content calendars, and a week-one action plan. It is a one-off payment of 14.99 pounds with lifetime updates. Take a look here.

Get started today

If you take one thing from this post, let it be this: stop repeating yourself to AI. If you are pasting the same instructions over and over, build a custom GPT. It takes 10 minutes and it will save you hours over the coming weeks.

Start with your most repetitive task. Follow the steps above. Get the instructions right. And then watch how much smoother your AI workflow becomes.

If you get stuck or want help building custom GPTs for your business, get in touch. We have set these up for businesses of all sizes and we are always happy to help.