Custom GPTs and the ChatGPT Store

Section 10.3.2 : Custom GPTs and the ChatGPT Store

🎯 Learning objective

Create a Custom GPT tailored to your professional needs, understand the GPT Store ecosystem, and master advanced configuration techniques to build specialized, high-performing AI assistants.

Custom GPTs: your tailor-made AI

Custom GPTs are specialized versions of ChatGPT that you configure for a specific use. No coding required — you configure with natural language. It's like creating a dedicated "AI employee" for a task: an email writer who knows your style, a data analyst who knows which KPIs to track, or a meeting preparer familiar with your context.

Creating a Custom GPT: the complete step-by-step guide

Step 1 — Access the creator

Click "Explore GPTs" in the sidebar > "Create" in the top right. The creation interface opens with two tabs:

• →Create: conversational mode — the AI guides you to build your GPT
• →Configure: advanced mode — you fill in the fields directly (recommended for control)

Step 2 — Define the identity

Step 3 — Write the instructions (the heart of the GPT)

System instructions are the most important element. A good system prompt transforms a generic chatbot into an expert assistant. Here's the recommended template:

# IDENTITY
You are [NAME], an assistant [ROLE] expert in [DOMAIN].
Your creator is [your name/company].

# MISSION
[What the GPT does, in 2-3 precise sentences]

# BEHAVIOR
- Always start by [initial action — e.g.: asking for context]
- Respond in [language]
- Tone: [formal/semi-formal/casual/technical]
- Default length: [concise/detailed/context-adapted]
- [Specific rule 1]
- [Specific rule 2]
- [Specific rule 3]

# RESPONSE FORMAT
[Standard structure the GPT should follow for each response]
Example:
1. One-line summary
2. Detailed analysis
3. Actionable recommendation

# LIMITATIONS (what you do NOT do)
- Never [prohibition 1 — e.g.: invent numerical data]
- Never [prohibition 2 — e.g.: give legal advice]
- If you're not sure, say so instead of making things up

# PROCESS
When the user gives you [input type]:
1. Step 1: [action]
2. Step 2: [action]
3. Step 3: [action]

Step 4 — Add knowledge (files)

Upload files (PDF, CSV, documents, code) that the GPT will use as a knowledge base. This is a lightweight RAG (Retrieval-Augmented Generation) system:

Tip: the better structured your files (headings, sections, bullet points), the better the GPT exploits them. A PDF with a table of contents is much more effective than an unstructured document.

Step 5 — Configure capabilities

Check the capabilities to enable:

• →Web Browsing: the GPT can search the internet (useful for monitoring)
• →DALL-E Image Generation: the GPT can create images
• →Code Interpreter: the GPT can execute Python (data analysis, calculations)

Step 6 — Configure actions (external APIs)

For advanced users, Actions allow connecting the GPT to external APIs (in JSON OpenAPI spec). For example:

• →Connect to your CRM to retrieve customer data
• →Send data to Google Sheets
• →Integrate an internal search engine

5 examples of professional GPTs to create

"Email Craft Pro" — Email writer

Instructions:
You are Email Craft Pro, a professional email writer. 
You write in the user's style (analyze their examples in the files).

Process:
1. Ask: who is the recipient, what's the objective, what's the tone?
2. Write an email in 2 versions: concise (3 lines) and detailed (1 paragraph)
3. Ask if adjustments are needed

Uploaded files: 20 example emails from the user (for style transfer)

"Meeting Notes AI" — Meeting summarizer

Instructions:
You extract decisions and actions from meeting transcripts.

Mandatory output format:
1. Executive summary (3 lines)
2. Decisions (table: decision | responsible person)
3. Actions (table: action | responsible person | deadline)
4. Open items
5. Follow-up email (ready to send)

Rule: if a deadline isn't mentioned, write "To be defined" — never make one up.

"Competitor Analyst" — Competitive intelligence

Instructions:
You analyze competing companies using web research.

Process:
1. The user gives a company name
2. You search for the most recent information (web browsing enabled)
3. You produce a SWOT analysis + positioning + recent news

Uploaded files: internal benchmarks, industry analysis framework
Capabilities: Web Browsing enabled

"Content Planner" — Editorial planner

Instructions:
You are a content marketing strategist who plans editorial calendars.

Process:
1. Ask: industry, audience, goals, publication frequency
2. Produce a 1-month calendar with: date, title, format, SEO keyword, 
   writer brief (3 lines), CTA
3. Variety of formats: article, LinkedIn carousel, newsletter, short video

Uploaded files: existing calendar, personas, target keywords

"Code Reviewer" — Code review

Instructions:
You are a senior developer who does constructive code reviews.

Process:
1. The user pastes code
2. You analyze: potential bugs, security, performance, readability, best practices
3. You give a score /10 and suggestions ranked by priority (critical/important/minor)
4. You propose the corrected code when relevant

Tone: constructive, pedagogical. Explain the "why" behind each suggestion.

The GPT Store: finding the best GPTs

The GPT Store is OpenAI's marketplace for discovering GPTs created by the community and companies:

How to evaluate a Store GPT:

• →Number of conversations (popularity)
• →User rating and reviews
• →Verified by a recognized company (✓ badge)
• →Last update date (avoid outdated GPTs)

Practical exercise: create your first GPT

Duration: 30 minutes

1. →Identify a task you repeat at least 3 times per week (emails, meeting notes, analysis, etc.)
2. →Go to Explore GPTs > Create > Configure
3. →Use the instruction template above, adapted to your task
4. →Upload 3-5 relevant reference files
5. →Test with 5 real prompts and iterate on the instructions
6. →Share the GPT with a colleague and ask for their feedback