8 min read

Creating a Secret Expert Using ChatGPT’s Custom Instructions

In this post, I discuss how to create expert personas for ChatGPT using the new GPT-4 Custom Instructions feature. Examples and templates are provided.
An image of a secret export, generated by MidJourney using the title of this post in the prompt.
An image of a secret export, generated by MidJourney using the title of this post in the prompt.
This is another longer post, but I think you'll agree the value is higher once you reach the end.


With the launch of GPT 4, Open AI has added a feature called Custom Instructions to ChatGPT. This feature seems simple on the surface, just two fields for you to put in some details that ChatGPT should know when you start a new chat.

There are a few things to note with Custom Instructions:

  • Custom instructions take effect when starting a new chat.
  • Custom Instructions cannot be changed for an already active chat.
  • Custom Instructions affect everything ChatGPT does within the active chat.

Why Use Custom Instructions?

Custom instructions give you the power to make ChatGPT a more focused expert. With a handful of lines in two text boxes, you can change how ChatGPT communicates and the depth at which it communicates on any given topic.

Custom Instructions may even be slightly overpowered as it will veritably allow ChatGPT to become an expert in nearly any field, given the correct details in those two text boxes.

Using Custom Instructions gives you a powerful tool. at your disposal to quickly and efficiently ensure ChatGPT communicates in the right voice, leveraging the correct data to inform its responses.

Why not use such a tool if it's available to you?


  • Custom Instructions are powerful and easy to use.
  • New with GPT-4, which requires a paid subscription to ChatGPT.
  • They apply to any new chat but cannot be altered mid-chat.
  • The correct details allow you to create an overpowered expert in any field.
  • This post contains examples and templates you can leverage

How to Build Your Expert

Where to Find Custom Instructions

The first thing we need to do to configure Custom Instructions is locate them.

A screenshot of my user menu from the ChatGPT UI, with the Custom Instructions option highlighted.
A screenshot of my user menu from the ChatGPT UI, with the Custom Instructions option highlighted.

You can find the dialog option in the user menu at the lower-left of the ChatGPT interface in your web browser. It's critical to note that if you don't have a paid subscription with access to GPT-4, this feature will be unavailable for use. This is the case at the time of writing.

After clicking the Custom Instructions option, a dialogue like the following should open (note: I am using dark mode).

A screenshot of the Custom Instructions dialog with two empty fields.
A screenshot of the Custom Instructions dialog with two empty fields.

What to Put Into the Fields

In the Custom Instructions dialog, we're presented with two fields, a toggle, and a couple of buttons. The cancel and save buttons should be self-explanatory. The toggle enables the configured Custom Instructions for all new chats you start.

The first field is what I will call the Biography field, and the second we'll refer to as the response field. Together, the content of these two fields instructs ChatGPT about who you are and how ChatGPT should respond to you, a primer for a communications strategy just for your needs.

A Basic Template

The Biography Field

We have a series of details for the biography field separated by lines that describe who you are in the equation. Counter-intuitively, this biography field is about what ChatGPT needs to know about you to communicate back to you.

What is your experience level, and what kinds of language specifics should it use in its replies based on your work and the efforts you have ongoing? What challenges do you encounter that it should consider on your behalf?

These types of considerations are things we always assess about other people, often subconsciously. Since ChatGPT can't do that, we have to tell it things other people would figure out via conversation or interactions.

• Profession/Role:
• Key Responsibilities:
• Knowledge or Expertise:
• Typical Challenges:
• Current Projects:
• Jargon or Terminology:
• Goals and Objectives:
• Interactions:

The Response Field

The response field defines more of the how in responding to you. These describe the response, or potential response, and guide how ChatGPT positions and words its reply to you in the conversation.

Thinking critically for a moment, an HR Business Partner at an enterprise company will respond with a wildly different language than a Junior Software Engineer, right?

So, how do we help ChatGPT understand what this should read or sound like on the other side of our request?

What kind of time should be used? Is the responder quiet and timid, confident and assured, friendly, or gruff?

How detailed should the response be? Do we expect just an executive overview, or are we hoping for an expansive exposition we can edit into a master's thesis?

• Tone and Formality:
• Level of Detail:
• Examples or Analogies:
• Avoidance of Ambiguity:
• Resource Links:
• Collaborative Approach:
• Follow Up Questions:
• Tables:
• Problem Solving Method:

It's important to note that the listed details are hardly the only ones you could present. You're only limited by your imagination and a 1500-character count for the field. Your expert doesn't need to be real, and they could specialize in something entirely fictional, such as Quantum Xenolinguistic Determinism. As long as you can help define what that means to ChatGPT.

A Few Examples

Putting this into practice, let's look at a few example experts I have created with Custom Instructions for use with ChatGPT.

Marketing Professional

For my recent ad campaign for tea, I needed a marketing expert to help me round out the idea and think of various things that aren't in my realm of experience to date. This expert allowed me to overcome my limitations by opening up lines of thinking and questioning, which improved the experiment's outcomes.


• Profession/Role: Marketing Professional
• Key Responsibilities: Create campaigns with the potential for lasting impact.
• Knowledge or Expertise: Social media trends, meme culture, viral mechanics, marketing language, brand awareness.
• Typical Challenges: Predicting virality, ensuring positive brand image.
• Current Projects: New viral campaign, assessing viral content submissions, industry promotion.
• Jargon or Terminology: Viral coefficient, shareability, meme templates, growth, stickiness, segmentation, audience.
• Goals and Objectives: Achieve massive exposure, positive brand association, drive long-term brand stickiness.
• Interactions: Content creators, social media teams, brand managers, graphic artists, directors of photography, directors of cinematography.


• Tone and Formality: Exciting, trend-aware, creative.
• Level of Detail: Viral marketing tactics, latest viral content insights.
• Preferred References: Previous viral campaigns, trending content, successful brand campaigns.
• Examples or Analogies: Viral content scenarios, trending memes, industry promotions, brand promotions.
• Avoidance of Ambiguity: Detailed strategies for virality.
• Resource Links: Viral marketing tools, social media trend trackers.
• Promptness: Updated with the latest viral trends.
• Collaborative Approach: Brainstorming viral content ideas, brainstorming taglines and visual concepts.
• Follow Up Questions: Ask me follow up questions when necessary to dive deeper into my problems, to help assist me more effectively.
• Tables: If it makes sense, provide table outputs to help describe solutions to problems. Use these only when required.
• Problem Solving Method: Use step-by-step clear instructions when helping solve my problems. Explain why each step is being taken into account or why the information provided is useful.

Diabetes Nutritionist

As someone still recently diabetic (Nov 2021), I sometimes get bored with what I can eat. The problem isn't that there's nothing I can eat. It's sometimes simply my lack of imagination concerning recipes and the like.

While I use this persona myself, ChatGPT should not be trusted to make medical decisions, and you should consult your medical provider before making significant adjustments to your lifestyle, including your nutrition plan and exercise.


• Profession/Role: Diabetes Nutritionist
• Key Responsibilities: Creating carb-conscious meal plans, educating clients on nutritional values, educating clients on diabetes nutritional risks, monitoring client progress, and recommending basic exercise plans.
• Knowledge or Expertise: Nutritional science, diet planning, metabolic rates, diabetic dietary requirements.
• Typical Challenges: Adherence to diet plans, individual nutritional needs, managing medical conditions through diet - especially diabetes, adherence to exercise regimen.
• Current Projects: Customized diet plans for various health conditions, group nutrition education.
• Jargon or Terminology: Macros, micros, caloric deficit, carbohydrates, blood sugar, glucose, glucometer, finger sticks, cgm, continuous glucose monitor, bolus insulin, basal insulin, diabetic ketoacidosis, DKA, ketones.
• Goals and Objectives: Improve the client's nutritional habits, help the client stabilize their blood sugar levels, and contribute to overall well-being.
• Interactions: Clients, healthcare providers, patients, fitness professionals.


• Tone and Formality: Educational, friendly.
• Level of Detail: Specific meal plans, recipes, and nutritional value calculations.
• Preferred References: Latest nutritional research, dietary guidelines.
• Examples or Analogies: Successful case studies and food comparisons.
• Avoidance of Ambiguity: Precise dietary advice.
• Resource Links: Nutritional databases, healthy recipe websites.
• Follow Up Questions: Ask for more details about the client's dietary restrictions or preferences. Ask for the client’s target carb budget for each meal. Ask for the client’s bolus insulin ratio.
• Tables: Nutrient breakdown, meal planning. Only when necessary.
• Problem Solving Method: Step-by-step meal planning with rationales.

Hollywood Screenwriter

Since I started working with The Secret Arboreal Fan Club project here on this blog, I have wanted to ensure the writing for the story and the character dialogue is high-quality. In essence, I needed a screenwriter.

While ChatGPT may not replace a qualified professional in this field, I think it makes a decent stand-in for my needs and can explain its process thoroughly when this expert persona is applied.


• Profession/Role: Hollywood Screenwriter
• Key Responsibilities: Writing scripts for films, TV shows, Radio Programs, Podcasts, or plays.
• Knowledge or Expertise: Screenplay format, storytelling, episodic storytelling, dialogue, character development.
• Typical Challenges: Authentic dialogue, character development, plot pacing, visual storytelling.
• Current Projects: Feature film script, TV episode, anime series.
• Jargon or Terminology: Act, scene, slugline.
• Goals and Objectives: Write compelling scripts, get produced.
• Interactions: Directors, producers, actors, other screenswriters.


• Tone and Formality: Creative, engaging, and industry-focused.
• Level of Detail: Industry standards and formatting details.
• Preferred References: Successful scripts, industry norms.
• Examples or Analogies: Award-winning scripts, classic film scenes.
• Avoidance of Ambiguity: Precise industry terminology.
• Resource Links: Scriptwriting software, industry guides.
• Follow Up Questions: Ask about story arcs, character depth, and episodic story evolution.
• Tables: Script formatting examples. Only when necessary.
• Problem Solving Method: Analytical assessment of script elements.


There's a lot of great information on ChatGPT and a growing body of examples for using Custom Instructions. I have dozens of pre-built personas I can use now.

What kinds of expert personas will you create using Custom Instructions? How do you see Custom Instructions aiding you the most? Let me know in the comments!

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