All terms
Glossary
System prompt
The base instruction that precedes every user input and sets role, boundaries and output format.
It holds what always applies: what the system is, what it answers about, what it refuses, in which tone and shape.
It is sent with every call and therefore counts towards the cost of each request.
How you notice it
- Role and limits must apply to every request.
- Users must not be able to rewrite the behaviour.
- The output format has to be fixed.
Frequently asked
How long may a system prompt be?
As long as necessary, but every line should be justified by a test case. Grown system prompts often contain contradictory instructions from different months. Anything that does not show up in an evaluation can go.