System Prompt
In one line
A system prompt is the instruction sent to an LLM before any user message, defining the assistant's role, tone and rules — effectively the AI product's character.
Going deeper
A system prompt is an instruction the user never sees, sent to the model before the conversation starts: 'You are Claude acting as the customer support assistant for this company. Reply in Korean. Do not quote prices.' It is where you define the AI's role, scope and rules.
For marketers, this is the highest-leverage lever in any AI product. The tone, accuracy and safety of your assistant mostly come down to how well the system prompt is written. Tuning it usually moves the needle faster than swapping models.
It is not an unbreakable wall, though. Prompt injection and jailbreaks can override it, so for sensitive policy enforcement layer the system prompt with separate guardrails rather than relying on it alone.
Related terms
Prompt Engineering
Prompt engineering is the practice of crafting inputs that steer an LLM toward better outputs — a way to dramatically change result quality without retraining the model.
LLMGuardrails
Guardrails are the layer of input/output checks added around an LLM to block unsafe responses, policy violations and leakage of sensitive information.
LLMPrompt Injection
Prompt injection is an attack where instructions hidden in untrusted data override the system prompt and force the LLM into unintended behaviour.
LLMJailbreak
A jailbreak is a prompt-level trick that bypasses an LLM's safety restrictions to force it into producing content the model is supposed to refuse.
LLMFew-shot Prompting
Few-shot prompting includes a small number of example inputs and outputs in the prompt itself, letting the LLM imitate the desired format or style without any retraining.
LLMPrompt Caching
Prompt caching reuses the computation done on a repeated system prompt or document so subsequent calls are dramatically cheaper and faster — a direct lever on operating costs for repetitive workloads like GEO monitoring.
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