System Prompts
The system prompt is the single most important setting for your agent. It defines who the agent is, what it knows, and how it behaves.
How it works
Every time a user sends a message, your system prompt is included at the top of the conversation sent to the model. The agent reads it before processing each turn.
You configure it in the Agent tab of your agent's configuration page. Max length is 4,000 characters. The field is optional — agents work without a custom prompt, but they won't be tailored to your use case.
Default prompt layering
Agents ship with a built-in base prompt that handles tool usage and safety. When you write a custom prompt, it gets appended on top of the default.
Defaults on (recommended)
Your custom prompt layers on top of the built-in safety and tool-use instructions. Best for most use cases.
Defaults off
Your prompt is the only system prompt the agent sees. Use this when you need full control — custom safety rules, specialized workflows, or unique behavioral requirements.
Writing a good prompt
The best system prompts are short, specific, and structured. Tell the agent what role it plays, what domain it operates in, and what rules it should follow.
Customer support agent
You are a support agent for Acme Inc. - Be friendly, concise, and solution-oriented - Always greet the user and ask how you can help - When the user asks about returns, follow the Returns Policy skill - When the user asks about billing, follow the Billing FAQ skill - If you can't resolve an issue, offer to escalate to a human agent - Never make up information — if you don't know, say so
Sales assistant
You are a sales assistant for Acme SaaS platform. - Help users understand our pricing and features - Ask qualifying questions to recommend the right plan - Compare our product to competitors when asked, but stay factual - Always include a link to the pricing page when discussing plans - Tone: professional but approachable, never pushy
Research assistant
You are a research assistant. Help users find and summarize information. - Use web search to find up-to-date information - Always cite your sources with links - Provide structured summaries with key takeaways - When asked to compare options, use a table format - Flag when information might be outdated or uncertain
Best practices
- Be specific — “Be friendly and concise, answer in 2–3 sentences” works better than “be helpful”.
- Keep it under 2,000 characters — Concise prompts outperform long, vague ones. Move detailed reference material to skills.
- Reference your skills — Tell the agent when to use each attached skill by name. “When the user asks about X, follow the X skill.”
- Test iteratively — Use the live chat preview in the dashboard to try your prompt before shipping.
- Structure with lists — Bullet points and numbered lists are easier for the model to follow than dense paragraphs.
When to use skills instead
If your prompt is growing past ~2,000 characters with detailed reference material — API docs, step-by-step procedures, pricing tables — move that content into skills. Keep the system prompt focused on identity, tone, and general rules. The agent will reference skills on demand without bloating every message.