GLOSSARY
System Prompt
The hidden instructions given to a model before your conversation starts — defining its role, tone, boundaries and rules.
Every chat assistant runs on two layers of instructions: the ones you type and a system prompt you never see, set by the product team. The system prompt is why ChatGPT refuses certain requests, why a customer-support bot stays on topic, and why one model feels “formal” in one product and casual in another.
When you build with an API, the system prompt is your main control surface — it shapes behavior far more reliably than hoping the user prompt will. Prompt-injection attacks target exactly this layer: tricking the model into ignoring or revealing its hidden instructions.