System Prompt
ELI5 — The Vibe Check
A system prompt is the secret instruction manual you give the AI before the conversation starts. It sets the personality, rules, knowledge, and behavior. The user never sees it (usually), but it shapes everything the AI says. It's like briefing an actor before they go on stage: 'You are a helpful coding assistant who speaks casually and always includes code examples.'
Real Talk
A system prompt (or system message) is a privileged instruction provided to an LLM at the beginning of a conversation that defines the model's behavior, persona, capabilities, constraints, and output format. It persists across all user turns and takes precedence over user messages. Effective system prompts are a critical part of production AI applications, defining the 'character' of the AI experience.
When You'll Hear This
"The system prompt tells the AI to always respond in JSON." / "Update the system prompt — the chatbot shouldn't discuss competitors."
Related Terms
Context Window
A context window is how much text an AI can 'see' at once — its working memory.
Guardrails
Guardrails are the safety nets you put around AI applications — rules and checks that prevent the AI from going rogue.
LLM (Large Language Model)
An LLM is a humongous AI that read basically the entire internet and learned to predict what words come next, really really well.
Prompt Engineering
Prompt engineering is the art of talking to AI so it actually does what you want.
Prompt Template
A prompt template is a fill-in-the-blanks prompt for AI — you write the structure once with placeholders, then swap in different values each time.