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AI at Scale: How to Write Custom GPTs for Marketing & Consulting

Doug Hunter

INTRODUCTION

When working with your favorite AI, do you know when to use Prompts, Custom GPTs, or Agents? Knowing that answer could save you a lot of time and hassle! Here is a quick decision tree to help accelerate the benefits of AI in your daily routines:

  • If you’re asking ChatGPT one question, once, then write a prompt. 
  • If you want ChatGPT to do a “thinking” task repeatedly, then build a Custom GPT.
  • If you want ChatGPT to complete a series of tasks across multiple systems, then construct an agent.

For me, I could see using my “Risk Factor Analysis” prompt repeatedly. So, I built a “Risk Factor GPT.” Below is the process I went through to build that Custom GPT, along with the learnings that came from some painful iterations. (I was amazed at how deeply ChatGPT can see, explain, and solve problems when going through the building process. Given that, I was also amazed at how difficult it could be for ChatGPT to do some pretty basic tasks.)

THE PROCESS

Rather than trying to navigate all the forms, options, and tools involved in building a Custom GPT, I instead asked ChatGPT to help me through the process. Below is my experience.

  • A few technical notes:
    • To create a Custom GPT, I had to upgrade my ChatGPT subscription from “Free” to “Plus.” 
    • I built the Custom GPT in OpenAI’s “Atlas” browser and did final testing using Chrome and a “Free” ChatGPT account.

First, I uploaded my detailed prompt into ChatGPT and told it about my goals for the Custom GPT. In turn, ChatGPT independently did the following:

  • Translated my prompt into the detailed instructions that the Custom GPT would need. (Note how ChatGPT’s instructions are so much more technical than what I wrote. To me, it validated using ChatGPT to build the Custom GPT instead of trying to build it on my own.)
  • Drafted the needed title, description, and conversation starters.
  • Wrote detailed instructions for how to build a Custom GPT and sent me to the Custom GPT Builder.

The Custom GPT Builder has two modes:

  1. Create: allows you to build a Custom GPT using a chatbot, and
  2. Configure: provides templates and settings that allow you to manually build your Custom GPT at a more granular and technical level.

I primarily used the “Create” mode and interacted with the Custom GPT Builder via chat, uploading the snippets that ChatGPT had created for me. However, I switched over to “Configure” mode several times because it was faster to type the text I wanted into a template than to painstakingly explain it to the chatbot.

After my Custom GPT was built, I ran numerous tests to see if I could break it.  Which I did, numerous times. Some of the issues were quite technical, e.g. people using a free version of ChatGPT are restricted by OpenAI from accessing the EDGAR API. In each case, I was eventually able to solve the problems using the interactive “Create” mode.

Here is the final “Risk Factor GPT.” (I also recently built a branded “Robot Image Generator GPT.”)

This description of the Custom GPT building process is short. But that masks that it took me over six hours of iteration to build this Custom GPT.  The next one will be much faster since there was a lot of first-time learning here…

SO MANY LEARNINGS

A lot of learning comes from encountering and overcoming problems. 

  • Make your images outside of the Custom GPT creation process. 
    • The hero and icon images that ChatGPT created were uninspiring and odd. Try Ideogram or Nano Banana instead.
    • I also had multiple problems trying to upload my company logo and bug to ChatGPT. These problems ranged from rights issues (on my own IP!) to ChatGPT creating a literal picture of a bug…
  • Review everything that ChatGPT generates.
    • Sometimes it is wrong. For example, ChatGPT generated a 600+ character description even though the Custom GPT Builder has a 300-character limit.
    • Sometimes it is off-point. The “Conversation Starters” that it generated never made sense…
    • Sometimes it doesn’t match your intent. For example, in another case, I wanted the Custom GPT to ask the user eight very specific questions. Instead, the Custom GPT Builder created eight new questions.
  • If you are using a paid version of ChatGPT, e.g. Plus or Pro, update the name on your credit card to the name you want as the author of your Custom GPT.
    • When I published my Custom GPT, the author name was my full legal name, not “Doug Hunter.” After some sleuthing, I figured out that the Custom GPT Builder automatically pulls your credit card name for the author name. So, I had to go back into ChatGPT’s account settings and change the name on my credit card.
  • Test your Custom GPT using both paid and free ChatGPT accounts.
    • It should have been obvious, but I accidentally discovered that the “Paid” and “Free” versions of ChatGPT have very different limitations. For example, in “Plus” I could use the EDGAR API to pull down the SEC filings, but that didn’t work in “Free.” So, I had to modify the instruction set to get my Custom GPT to work for “Free” users. Unfortunately, the quality of results is lower on the Free version…
    • Another takeaway from this problem: pay for an upgraded version of ChatGPT – even if you are not writing Custom GPTs, you will get richer answers and better capabilities.
  • Think critically!
    • When solving a particular problem, the chatbot said, “There are only three ways to fix the problem. Pick one!” However, all three of those options required trade-offs that I was not willing to make. Instead, I designed a fourth way and had the chatbot implement it. Don’t accept what the chatbot tells you as necessarily true. Bring some human intelligence to the problem!
  • At the end, recheck every field and block of text in your Custom GPT. 
    • When you make substantive edits to your Custom GPT, the Builder automatically rewrites your title, description, and conversation starters – often to text that is off-target and less descriptive. You must go back and review all these text blocks in the Builder’s “Configure” mode and manually roll back any undesired changes. 
    • You can make this task easier by saving copies of your preferred title, description, and conversation starters in a separate document.

IN CONCLUSION

Writing a Custom GPT nicely automates repeated tasks and allows you to share that functionality with your team and others – accelerating the benefits of AI in daily work. However, it takes time and expertise. So, first, I suggest that you write a Custom GPT only if you are certain that it will be used repeatedly.  

Second, don’t try to write the Custom GPT on your own – use the built-in chat functionality. It’s not perfect, but unless you are an AI coding genius, it’s the fastest way to go. 

Finally, you are closer to Custom GPT mastery than you think! Which of your prompts do you use repeatedly and should upgrade to a Custom GPT?

AI Content Statement

All text in this post is human generated, written by me. The image was generated by ChatGPT-5.2 via the Custom GPT “Robot Image Generator.”

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