LLM Fundamentals

What is a System Prompt?

A system prompt is hidden instructions provided to AI before your conversation that shape its behavior, personality, and capabilities—like giving an employee their job description before they start work.

Understanding System Prompts

Every AI conversation has two types of input: the system prompt (background instructions) and user prompts (your messages). The system prompt runs silently before you type anything, establishing who the AI "is" for this conversation.

When ChatGPT maintains a consistent personality across millions of users, that's a system prompt at work. When Claude refuses certain requests, that's system prompt guardrails. And when you use Custom Instructions, you're adding your own layer to the system prompt.

How System Prompts Work

The conversation structure AI sees:

System Prompt (Hidden)

"You are a helpful real estate assistant with expertise in Nashville markets. Always respond professionally. Never provide legal or financial advice..."

↓

User Prompt (Your Message)

"Write a listing description for 123 Main Street."

↓

AI Response

"Welcome to 123 Main Street, where Nashville charm meets modern convenience..."

Where to Set System Prompts

ChatGPT

Settings → Personalization → Custom Instructions

  • • "What would you like ChatGPT to know about you?"
  • • "How would you like ChatGPT to respond?"
  • • Limited character count

Claude

Create a Project → Add custom instructions

  • • Longer instruction limits
  • • Can upload reference documents
  • • Project-specific contexts

Manual Method

Paste instructions at conversation start

  • • Works with any AI
  • • Maximum flexibility
  • • Requires copy/paste each time

API Access

Include "system" message in API calls

  • • Full programmatic control
  • • For custom applications
  • • Most powerful option

System Prompts for Real Estate Agents

Context Cards are essentially enhanced system prompts. When you load your Context Card at the start of a conversation, you're giving AI background instructions about who you are, how you communicate, and what you know.

Example System Prompt for Agents

Role: You are a real estate content assistant for [Agent Name], a luxury agent in Nashville, TN with 15 years experience.

Voice: Write in a warm, conversational tone. Use "you" and "your" frequently. Avoid: "dream home," "won't last long," "stunning."

Expertise: Nashville neighborhoods (Green Hills, Belle Meade, Franklin), relocation buyers, first-time homebuyers.

Constraints: Never provide legal or financial advice. Always suggest consulting professionals for those topics. Keep emails under 200 words unless specified.

Frequently Asked Questions

What is a system prompt in AI?
A system prompt is hidden instructions given to AI before your conversation begins. It defines the AI's role, personality, and rules. When you use ChatGPT's Custom Instructions or Claude's Projects, you're writing a system prompt. It's like giving an employee their job description before they start work.
What is the difference between a system prompt and a regular prompt?
A regular prompt is your in-conversation request ("Write me an email"). A system prompt is pre-conversation setup that shapes ALL responses. System prompts define who the AI "is"—regular prompts tell it what to do. System prompts persist across messages; regular prompts are one-time requests.
Can I see what system prompts AI tools use?
Generally, no. Companies like OpenAI and Anthropic keep their default system prompts confidential. However, you can add YOUR instructions on top of theirs. Your Custom Instructions combine with the base system prompt to create the final AI behavior you experience.
How are system prompts different from Context Cards?
Context Cards are a more structured, comprehensive approach to system prompts. A basic system prompt might be a few sentences; a Context Card is an organized document with layers (identity, knowledge, style, constraints). Think of Context Cards as system prompts with a proven architecture.

Related Concepts

AI Acceleration Frameworks

Context Cards

Enhanced, structured system prompts for consistent AI voice.

 LLM Fundamentals

Prompt

The user-facing input that works with system prompts.

 AI Acceleration Frameworks

Context Engineering

The broader practice of shaping AI behavior.

 Prompting Techniques

Role Prompting

Assigning AI a specific persona—often done in system prompts.

Related Articles

Blog

Context Engineering Guide

How system prompts power context engineering.

 Blog

Context Card Tutorial

Build system-level context cards for consistent AI results.

Sources & Further Reading

Master System Prompts

Learn to write effective system prompts and Context Cards in The Architect workshop—create AI that consistently sounds like you.

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