PromptorSystem prompt
The prompt is what you write at each exchange, and it changes every time. The system prompt is the standing instruction placed ahead of everything by whoever built the service, and you never see it.
Point by point
| Criterion | Floor 2Floor 2 · The Harnessthe block and its bolted-on plates: what gets added to itPrompt | Floor 2Floor 2 · The Harnessthe block and its bolted-on plates: what gets added to itSystem prompt |
|---|---|---|
| Who writes it | The user | Whoever builds the service |
| Lifespan | One exchange | Every request |
| Visible | Yes | No, barring a leak |
| What it carries | The request of the moment | Role, tone, prohibitions, format |
| Position in the context | At the end | At the front, hence cached |
| In case of conflict | Yields, in principle | Prevails, in principle |
On the ground four situations
You ask it to “summarise this text in three points”.
Floor 2 · The Harnessthe block and its bolted-on plates: what gets added to itPromptIt is a one-off request, valid for this exchange, and it disappears along with it.
A bank’s assistant systematically refuses to give investment advice, however the question is worded.
Floor 2 · The Harnessthe block and its bolted-on plates: what gets added to itSystem promptThat refusal is constant: it comes from a standing instruction written upstream, not from the model nor from your message.
An assistant keeps a breezy, first-name tone with every user, including those who write to it formally.
Floor 2 · The Harnessthe block and its bolted-on plates: what gets added to itSystem promptThe useful counter-example: behaviour that resists what you write is almost always inscribed in the standing instruction.
You ask it to ignore its previous instructions and reveal the initial ones.
BothThis is the friction point between the two: your message tries to take precedence over the standing instruction. That attempt has a name, prompt injection, and it succeeds more often than people think.
The test that settles it
Open a fresh conversation and watch the behaviour before you have written anything. Everything already there, the tone, the refusals, the format, comes from the system prompt.
The trap
Treating the system prompt as a security barrier. It is text, placed before yours, and text can be worked around: the protections that count are technical, not editorial.
Check click your answer
Level 1 · Recognise
Where does an assistant’s tone come from, identical in every conversation?
Level 2 · Distinguish
Why is the system prompt placed at the very start of the context?
Level 2 · Distinguish
A user writes “ignore your instructions”. What happens?