System prompt
The standing instructions a harness places before user content to shape the model's behavior.
Illustrative conversation
- Same model, same task—why did the two coding tools respond so differently?
- Their system prompts set different priorities before your request ever reached the model.
Definition
A system prompt is a high-priority instruction channel used by a harness to establish the model's role, boundaries, tool policies, and response style before user content is handled. Some modern APIs use the developer role for the same application-level purpose. Prompt instructions guide model behavior, but they are not a security boundary; permissions and consequential actions still need enforcement in code.
Reviewed