Build Your Own Custom GPT in Under 30 Minutes - Step-by-Step Beginner's Guide

A friendly guide to building your personalised ChatGPT assistant (custom GPT creation) in under 30 minutes

The Quick Essentials

Before we dive in, here's what you need to know:

You'll need a ChatGPT Plus or Enterprise account (the paid version),Creating a custom GPT involves naming it, giving it a personality, uploading knowledge files, and enabling tools,The entire process happens at chat.openai.com/gpts,No coding required — just plain English instructions,You can keep your GPT private, share it via link, or publish it in the GPT Store

Step 1: Getting Access

First things first, you need a ChatGPT Plus subscription:

Head over to chat.openai.com,Click "Upgrade to Plus" if you haven't subscribed yet,Confirm your plan and payment (USD $20/month at the time of writing)

Once you're all subscribed:

Navigate to: chat.openai.com/gpts,Click the black "Explore GPTs" button in the left menu,At the top right, click "Create"

Brilliant! You're now in the GPT Builder interface where all the magic happens.

Step 2: Starting in "Create" Mode

You'll see a chat interface asking: "What would you like to make?"

This is where you describe your GPT in plain language. For example:

"I'd like to create a friendly GPT that helps junior marketers in the UK write social media copy. It should use casual British English and understand cultural references from across the UK."

The system will respond with follow-up questions like:

What tone should it use?,Should it browse the internet or run code?,Will you upload any knowledge files?

Answer naturally and conversationally. The system builds a draft GPT based on your answers.

It may even recommend a name and an image:

Once the chat version feels roughly right, click "Configure" in the top bar to manually fine-tune everything.

Step 3: Configuring Your GPT

This is the control panel where you can edit every setting. Follow these steps:

3.1 — Name Your GPT

In the Name field: give it a clear name like "Brit Copy Buddy",In Description: write what it does — "Helps junior UK marketers write scroll-stopping social copy in casual British English."

3.2 — Write the Instructions

Scroll down to the Instructions box and type your behaviour settings. Think of this like a personality manual. If you followed the steps, then it may well already be filled in for you. This is where the magic happens, so make sure it truly reflects your purpose. Because it is so important, we created a separate guide for this which you can read here. For example:

This GPT is a friendly and culturally aware assistant designed to help junior marketers in the UK write engaging social media copy. It communicates in a casual, approachable tone using British English, including regionally familiar slang and references from across England, Scotland, Wales, and Northern Ireland. It provides clear, supportive guidance to help users improve their writing, offering creative suggestions while keeping brand voice and audience in mind. It can reference UK cultural events, holidays, humour, and idioms to make content feel local and relevant. It avoids Americanisms and ensures that grammar, spelling, and phrasing are aligned with UK standards. The assistant will ask for context when needed (e.g., target audience or platform), and will aim to keep things breezy, witty, and scroll-stopping.

3.3 — Add Conversation Starters

Under Conversation Starters, add 3–4 useful prompts users might click on:

"Help me write a tweet for a UK skincare brand launch","Can you make this Instagram caption sound more British?","Draft some TikTok captions about a new meal deal"

This helps users jump straight in without typing from scratch.

Step 4: Adding Custom Knowledge (Optional but Recommended)

If you want the GPT to reference your own documents — like brand guidelines or FAQs — follow these steps:

Scroll to the Knowledge section,Drag and drop your files (accepted formats: .pdf, .txt, .csv, .md, .json),Upload limit is around 20 files at present

Example: Upload a "Tone of Voice Guide.pdf" and your GPT will use it to match your brand style.

Important note: Your GPT can reference but not quote files word-for-word. It learns the content conceptually rather than memorising exact phrases.

We have created a step-by-step guide for the best way to structure your Knowledge files here.

Step 5: Enabling Tools

Now choose which abilities your GPT should have.

Scroll to Capabilities, and toggle the following:

✅ Web Browsing — useful for real-time info like news or trends,✅ Code Interpreter — for handling files, calculations, data plots,✅ Image Generation — if you want it to create pictures (e.g., Instagram ideas),✅ File Uploads — lets users feed the GPT spreadsheets or PDFs

Select only what's genuinely useful — too many tools can make your GPT's responses confusing.

Step 6: Testing Your GPT Thoroughly

Before publishing, have a proper chat with your GPT.

Ask both straightforward and unusual questions to test:

Does it maintain the right tone?,Does it understand your uploaded files?,Does it use tools properly (like making charts or browsing)?,Does it clarify things when uncertain or guess incorrectly?

If anything feels off, go back to the Instructions and tweak your wording. Even changing one line can make a significant difference. You might find some of the tips in our article on How People Really Use AI in 2025 useful here.

Step 7: Create New Action

This function allows you to turn your GPT into a powerful API-aware assistant that can fetch data, trigger services, or complete tasks — all from inside the chat.

This is an optional extra when creating a Custom GPT and is complicated enough to need its own guide, which you can read here.

If this is your first attempt at creating a Custom GPT, we suggest skipping this step for now and moving on to Step 8.

Step 8: Switch Off Training

You should always consider anything sensitive you share with any AI chatbot. However, its always a good idea to switch off the request to improve the AI models. For more on the broader implications of AI training and data, consider this research paper on the ethical considerations of AI training data.

Step 9: Publishing Your GPT

At the bottom right, click the "Publish" button.

You'll be asked to choose:

Private — only visible to you,Unlisted — only people with your link can access it,Public — listed on the GPT Store for anyone to use

Give it a thumbnail image (upload one or use the auto-generated option), choose a category (e.g., Marketing, Productivity), and confirm.

Congratulations! Your GPT is now live and you can view it.

Final Tips for Success

🧹 Keep it focused — One GPT = one clear purpose,🪪 Use your brand voice — match the tone your users expect,🔁 Iterate regularly — update your files and instructions as you learn what works,💬 Share wisely — use private/unlisted first before going public

Happy GPT creating! With these steps, you'll be up and running with your custom assistant in no time. You might also want to explore how AI Agents Will Break Passkeys And 3 Ways To Fix Them to understand more about advanced AI functionalities.

You may also find useful:

How to Upload Knowledge into Your Custom GPT,How to Use the “Create an Action” Feature in Custom GPTs,Or try this playbook out now at ChatGPT by tapping here.