System prompts

A system prompt shapes how Finn responds — its tone, format, and persona. The SDK lets you set one at two levels, both optional. If you set neither, Finn uses the backend’s default.

Client-level default

Set systemPrompt on the client to apply it to every new conversation that client starts:

const finn = new FinnClient({
  url,
  apiKey,
  systemPrompt: 'Answer concisely. Prefer numbers and short bullet points.',
});

Per-conversation override

Pass systemPrompt to sendMessage() to override the default for one conversation:

const turn = finn.sendMessage('Summarize member growth this quarter.', {
  systemPrompt: 'You are a credit union analyst. Be formal and cite figures.',
});

The one rule: new conversations only

Caution

A system prompt is honored only when a conversation is created — i.e. on the first message of a conversation (no conversationId yet). Passing systemPrompt together with an existing conversationId has no effect; the conversation keeps the prompt it was created with.

So the precedence for a brand-new conversation is:

1. sendMessage(text, { systemPrompt }) — the per-call override, if given;
2. otherwise the client’s systemPrompt default, if set;
3. otherwise the backend’s built-in default.

To apply a different system prompt, start a new conversation (omit conversationId).