System Prompt | behavior.engineering

The system prompt is how a product builder configures a model’s behavior for their specific use case. It typically defines the model’s persona, the task it should focus on, how it should handle edge cases, and what it should or shouldn’t do — all before the user says anything. A well-written system prompt can dramatically shape how a model behaves: the same underlying model can act as a cautious legal assistant or a playful creative partner depending on how the system prompt frames its role. For behavior architects, the system prompt is the primary lever available at deployment time, and writing effective system prompts requires understanding both the model’s tendencies and the user’s needs.

System Prompt ArchitectureA template and framework for structuring system prompts — the primary technical instrument for controlling AI behavior in deployed products.
Prompt EngineeringThe practice of crafting and refining the text given to a model — instructions, examples, context — to reliably produce desired outputs.
Context EngineeringThe broader practice of designing what information a model has access to at inference time — including instructions, memory, tools, and retrieved content.
Behavioral SpecificationA written document or set of guidelines that defines how a model is expected to behave across different situations.
Instruction FollowingA model's ability to accurately understand and comply with the directions given to it in a prompt.
Meta-PromptA prompt designed to generate or improve other prompts, rather than directly produce the final task output.