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Tendril · Builders · AI Foundations

AI and the Hidden Instructions Every AI Has

Every chatbot has a 'system prompt' you can't see that shapes how it answers.

40 min · Reviewed 2026

The big idea

Behind every chatbot is a hidden system prompt — instructions the company gave the AI before you ever typed. That's why ChatGPT 'feels' different from Claude.

Some examples

A system prompt sets tone, refusals, and persona.
You can't see the system prompt directly in most chatbots.
Custom GPTs let you write your own system prompt.
The system prompt is why an AI may refuse certain topics.

Try it!

Open ChatGPT or Claude. Ask 'what are your default instructions?' Notice how vague the answer is — that's the hidden system prompt at work.

AI and system vs user prompts: the hidden layer running every chat

The big idea

Every AI chat has two layers: the system prompt that sets the rules (you don't see it) and the user prompt that's what you type. Knowing this explains why ChatGPT and Claude act so differently with the same question.

How to use it

Ask AI to explain what a system prompt usually contains
Ask AI to describe how its own behavior is shaped by one
Ask AI to compare 2 chatbots and guess their system prompt vibes
Build your own system prompt for a custom GPT

Try it

Build your own custom GPT (or Project) with a 5-line system prompt. Compare its behavior to the default.

What's a 'System Prompt'? The Hidden Instructions Shaping Every Reply

The big idea

ChatGPT's 'You are a helpful assistant' is a system prompt. Claude's is much longer. Knowing they exist is how you start customizing AI for real.

Some examples

ChatGPT 'Custom Instructions' replaces parts of the system prompt
Claude Projects let you set a custom system prompt per project
Poe lets you build a bot with any system prompt you want
System prompts are why GPT in Cursor 'feels different' from ChatGPT

Try it!

Open ChatGPT settings → Personalization → Custom Instructions. Write 3 lines about how you want it to talk to you. Test the difference.

The 'System Prompt' Is Why ChatGPT and Claude Act Different

The big idea

Every conversation with ChatGPT, Claude, or Perplexity starts with a hidden 'system prompt' — instructions the company wrote telling the AI how to behave. That's why the same underlying model behaves like 'helpful tutor' in one app and 'sassy friend' in another. When you build with the API, you write your own system prompt.

Some examples

ChatGPT's system prompt is leaked online: it includes 'be helpful,' 'follow safety guidelines,' 'use markdown for formatting.'
Custom GPTs and Claude Projects let you write your own system prompt — that's literally how they're built.
Snap's My AI uses GPT-4 with a heavily customized system prompt that gives it the 'fun friend' personality.
If you can write a clear 1-paragraph system prompt for your own GPT, you've done the same thing as 80% of 'AI app' startups.

Try it!

On chatgpt.com, click 'Explore GPTs' → 'Create.' The 'Instructions' box is the system prompt — write a 5-line spec for a useful tool ('always answer in 3 bullets,' 'never use jargon'). You just shipped a custom AI app.

What 'System Prompt' Does (and Why Every Custom GPT Has One)

The big idea

Every AI you talk to has a hidden 'system prompt' — a long instruction the company wrote that tells the model how to behave (e.g., 'You are ChatGPT, a helpful assistant. Refuse to do X. Always cite Y.'). When you make a Custom GPT or Claude Project, you're writing your own system prompt on top. This is why the same underlying model (GPT-4o) can act totally different depending on which app you're using. Knowing this lets you build your own AI tools — and lets you understand why some chatbots feel friendly and others feel stiff.

Some examples

Anthropic publishes Claude's full system prompt at anthropic.com/news — you can read exactly what behavior is hard-coded.
OpenAI's Custom GPT builder is just a UI for writing a system prompt + uploading files — that's the entire 'magic.'
When someone shares a 'jailbreak' prompt that seems to free the AI, they're trying to override the system prompt — the company logs and patches these.
You can build a Custom GPT in 5 minutes (free in ChatGPT) with a system prompt like 'You are an AP US History tutor for a teen. Answer in Socratic style.'

Try it!

In ChatGPT, open the Explore GPTs page and pick any popular Custom GPT. Click 'View' to see the system prompt the creator wrote. That's the whole secret.

End-of-lesson check

15 questions · take it digitally for instant feedback at tendril.neural-forge.io/learn/quiz/end-builders-foundations-AI-and-system-prompts-vs-user-prompts

Which statement best describes what a system prompt does?
1. It is a warning message that appears when an AI makes a mistake
2. It is a feature that lets you copy and paste information into an AI
3. It is a hidden set of instructions that shapes how an AI responds to users
4. It is the text you type when you are having a conversation with an AI
Why does ChatGPT feel different from Claude when you talk to them?
1. They were trained on the exact same data
2. Users can vote to change their personalities
3. One of them is older than the other
4. They have different system prompts written by their companies
Who writes the system prompt for a chatbot like ChatGPT or Claude?
1. The user each time they start a conversation
2. The AI writes it for itself automatically
3. An independent group of testers
4. The company that created the AI
What is a user prompt?
1. The hidden instructions that tell the AI how to behave
2. The text you type when having a conversation with an AI
3. A rule that prevents the AI from making mistakes
4. A message that appears when the AI refuses to answer
If you ask an AI 'what are your default instructions?', what kind of answer should you expect?
1. A refusal to answer because the question is forbidden
2. A vague answer that doesn't reveal the actual system prompt
3. A list of all the company's rules
4. The exact, complete text of the hidden system prompt
A student notices that Claude will not help them write harmful content, but Claude will help with homework. What explains this difference?
1. The student didn't type the request correctly
2. Claude checks the internet before answering
3. The system prompt tells Claude to refuse certain topics
4. Claude is smarter than other AI tools
What is a persona in the context of AI?
1. The physical appearance of a robot using AI
2. A username on an AI platform
3. The character or personality style the AI is programmed to show
4. A type of error message
A company releases a new AI assistant and wants it to always be friendly and never insult users. Where would they put these instructions?
1. In the user prompt
2. On their website footer
3. In a separate document the user must download
4. In the system prompt
What is a Custom GPT?
1. A GPT that costs extra money to use
2. A version of ChatGPT where you can write your own system prompt
3. A GPT that is more intelligent than regular GPT
4. A GPT that only works on custom computers
What tool from Anthropic allows users to write their own system instructions?
1. An email service
2. Claude Projects
3. A website builder
4. A video editor
Can you see the exact system prompt in most chatbots you use online?
1. Yes, it appears in the chat window
2. No, it is hidden from users
3. No, but you can find it in the settings menu
4. Yes, but only after you pay
Why might two different AI chatbots give different answers to the same question?
1. One of them is broken
2. They flip a coin to decide answers
3. They have different system prompts that shape their responses
4. They are both reading from the same script
A teacher creates a Custom GPT that always answers in the tone of a helpful tutor. Where does this instruction live?
1. In the Custom GPT's system prompt
2. In every student's user prompt
3. In the GPT's name
4. In the school handbook
What does it mean that the system prompt is 'hidden'?
1. The AI cannot see its own instructions
2. The instructions are encrypted
3. The instructions are deleted after each conversation
4. Users cannot directly see or read the instructions
Which feature lets regular users customize how an AI behaves without programming?
1. A code editor
2. A music player
3. A math calculator
4. Custom GPTs or Claude Projects

← Back to interactive lesson

Tendril · Builders · AI Foundations

AI and the Hidden Instructions Every AI Has

Every chatbot has a 'system prompt' you can't see that shapes how it answers.

40 min · Reviewed 2026

The big idea

Behind every chatbot is a hidden system prompt — instructions the company gave the AI before you ever typed. That's why ChatGPT 'feels' different from Claude.

Some examples

A system prompt sets tone, refusals, and persona.
You can't see the system prompt directly in most chatbots.
Custom GPTs let you write your own system prompt.
The system prompt is why an AI may refuse certain topics.

Try it!

Open ChatGPT or Claude. Ask 'what are your default instructions?' Notice how vague the answer is — that's the hidden system prompt at work.

AI and system vs user prompts: the hidden layer running every chat

The big idea

How to use it

Ask AI to explain what a system prompt usually contains
Ask AI to describe how its own behavior is shaped by one
Ask AI to compare 2 chatbots and guess their system prompt vibes
Build your own system prompt for a custom GPT

Try it

Build your own custom GPT (or Project) with a 5-line system prompt. Compare its behavior to the default.

What's a 'System Prompt'? The Hidden Instructions Shaping Every Reply

The big idea

ChatGPT's 'You are a helpful assistant' is a system prompt. Claude's is much longer. Knowing they exist is how you start customizing AI for real.

Some examples

ChatGPT 'Custom Instructions' replaces parts of the system prompt
Claude Projects let you set a custom system prompt per project
Poe lets you build a bot with any system prompt you want
System prompts are why GPT in Cursor 'feels different' from ChatGPT

Try it!

Open ChatGPT settings → Personalization → Custom Instructions. Write 3 lines about how you want it to talk to you. Test the difference.

The 'System Prompt' Is Why ChatGPT and Claude Act Different

The big idea

Some examples

ChatGPT's system prompt is leaked online: it includes 'be helpful,' 'follow safety guidelines,' 'use markdown for formatting.'
Custom GPTs and Claude Projects let you write your own system prompt — that's literally how they're built.
Snap's My AI uses GPT-4 with a heavily customized system prompt that gives it the 'fun friend' personality.
If you can write a clear 1-paragraph system prompt for your own GPT, you've done the same thing as 80% of 'AI app' startups.

Try it!

What 'System Prompt' Does (and Why Every Custom GPT Has One)

The big idea

Some examples

Anthropic publishes Claude's full system prompt at anthropic.com/news — you can read exactly what behavior is hard-coded.
OpenAI's Custom GPT builder is just a UI for writing a system prompt + uploading files — that's the entire 'magic.'
When someone shares a 'jailbreak' prompt that seems to free the AI, they're trying to override the system prompt — the company logs and patches these.
You can build a Custom GPT in 5 minutes (free in ChatGPT) with a system prompt like 'You are an AP US History tutor for a teen. Answer in Socratic style.'

Try it!

In ChatGPT, open the Explore GPTs page and pick any popular Custom GPT. Click 'View' to see the system prompt the creator wrote. That's the whole secret.

End-of-lesson check

15 questions · take it digitally for instant feedback at tendril.neural-forge.io/learn/quiz/end-builders-foundations-AI-and-system-prompts-vs-user-prompts

Which statement best describes what a system prompt does?
1. It is a warning message that appears when an AI makes a mistake
2. It is a feature that lets you copy and paste information into an AI
3. It is a hidden set of instructions that shapes how an AI responds to users
4. It is the text you type when you are having a conversation with an AI
Why does ChatGPT feel different from Claude when you talk to them?
1. They were trained on the exact same data
2. Users can vote to change their personalities
3. One of them is older than the other
4. They have different system prompts written by their companies
Who writes the system prompt for a chatbot like ChatGPT or Claude?
1. The user each time they start a conversation
2. The AI writes it for itself automatically
3. An independent group of testers
4. The company that created the AI
What is a user prompt?
1. The hidden instructions that tell the AI how to behave
2. The text you type when having a conversation with an AI
3. A rule that prevents the AI from making mistakes
4. A message that appears when the AI refuses to answer
If you ask an AI 'what are your default instructions?', what kind of answer should you expect?
1. A refusal to answer because the question is forbidden
2. A vague answer that doesn't reveal the actual system prompt
3. A list of all the company's rules
4. The exact, complete text of the hidden system prompt
A student notices that Claude will not help them write harmful content, but Claude will help with homework. What explains this difference?
1. The student didn't type the request correctly
2. Claude checks the internet before answering
3. The system prompt tells Claude to refuse certain topics
4. Claude is smarter than other AI tools
What is a persona in the context of AI?
1. The physical appearance of a robot using AI
2. A username on an AI platform
3. The character or personality style the AI is programmed to show
4. A type of error message
A company releases a new AI assistant and wants it to always be friendly and never insult users. Where would they put these instructions?
1. In the user prompt
2. On their website footer
3. In a separate document the user must download
4. In the system prompt
What is a Custom GPT?
1. A GPT that costs extra money to use
2. A version of ChatGPT where you can write your own system prompt
3. A GPT that is more intelligent than regular GPT
4. A GPT that only works on custom computers
What tool from Anthropic allows users to write their own system instructions?
1. An email service
2. Claude Projects
3. A website builder
4. A video editor
Can you see the exact system prompt in most chatbots you use online?
1. Yes, it appears in the chat window
2. No, it is hidden from users
3. No, but you can find it in the settings menu
4. Yes, but only after you pay
Why might two different AI chatbots give different answers to the same question?
1. One of them is broken
2. They flip a coin to decide answers
3. They have different system prompts that shape their responses
4. They are both reading from the same script
A teacher creates a Custom GPT that always answers in the tone of a helpful tutor. Where does this instruction live?
1. In the Custom GPT's system prompt
2. In every student's user prompt
3. In the GPT's name
4. In the school handbook
What does it mean that the system prompt is 'hidden'?
1. The AI cannot see its own instructions
2. The instructions are encrypted
3. The instructions are deleted after each conversation
4. Users cannot directly see or read the instructions
Which feature lets regular users customize how an AI behaves without programming?
1. A code editor
2. A music player
3. A math calculator
4. Custom GPTs or Claude Projects

← Back to interactive lesson