System instruction

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What you will leave with

A system instruction is configuration context intended to guide a model’s behavior across a session or task, often with priority over ordinary user input.

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Find the one fact or relationship you need, then return to your original learning goal.

Do now on this pageClarify this conceptThe plan states the outcome, time, prerequisite, immediate action, and prepared continuation.Another valid routeInspect SourcesSee provenance, review, and evidence boundaries.

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Connected glossary

System instruction

A system instruction is configuration context intended to guide a model’s behavior across a session or task, often with priority over ordinary user input.

Plan for this page

Understand one concept in plain language and connect it to nearby ideas.

You will leave with: It can define role, constraints, available tools, refusal behavior, style, or process. It influences generation but is not a security boundary by itself and may conflict with data, tools, user content, or other controls.
Time: 3–8 min
Before you begin: No prerequisite. Keep one real example in mind.
Do this now: Read the explanation, then compare the example with the common misunderstanding.

Prepared next stepStudy context and control layers

System instructionA system instruction is configuration context intended to guide a model’s behavior across a session or task, often with priority over ordinary user input.

Prompt
Permission
Guardrail

Plain explanation

It can define role, constraints, available tools, refusal behavior, style, or process. It influences generation but is not a security boundary by itself and may conflict with data, tools, user content, or other controls.

Example

A support assistant receives a system instruction to answer only from approved documents and escalate account changes to a human.

Why it matters

System instructions help make product behavior consistent, yet confidential data, permissions, validation, and enforcement need separate mechanisms. A prompt cannot safely grant authority the system should not possess.

Common misunderstanding

Misconception: a system instruction makes prohibited behavior impossible. Correction: it is one behavioral control that requires testing and technical boundaries.

Related concepts

Follow relationships, not only the alphabet

PromptA prompt is input supplied to a generative model or system to shape the task, context, constraints, or desired output.PermissionA permission is an authorized ability to access information, use a tool, or perform an action under defined conditions.GuardrailA guardrail is a preventive, detective, or corrective control intended to keep system behavior within defined boundaries.

Study context and control layers

Sources and scope

What supports this object

Machine Learning GlossaryGoogle for Developers

Provides generative-AI instruction terminology; message roles, precedence and enforcement are implementation-specific.

Open source

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