> ## Documentation Index
> Fetch the complete documentation index at: https://docs.nixflex.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Writing a good agent prompt

> How to write a system prompt your agent will follow reliably

The system prompt defines your agent's behaviour, logic, and communication style. A clear prompt leads to consistent, predictable calls across both inbound and outbound agents.

## The golden rule

The prompt must explicitly define the behaviour you expect. If something is not written, do not expect it to happen consistently. Write every important step clearly, especially multi-step flows.

**Less reliable**

> If the caller can't make it, transfer them.

**Reliable**

> If the caller cannot attend, first ask whether they would like to reschedule or be transferred to reception. Only transfer after they confirm.

## You're in control

Your prompt gives you full control over how the agent behaves — its tone, its decisions, how it handles each situation, and when it uses actions. If you want it to do something a specific way, write it in the prompt and the agent will follow your instructions.

## Keep it focused

For best performance, keep prompts structured, clear, and concise.

* Recommended range: **800–1500 tokens**
* Keep prompts under **\~2000 tokens**

Long or repetitive prompts reduce clarity and can lead to inconsistent behaviour. You can use an LLM or internal tool to turn raw user input into a clean, structured prompt before saving it.

<Tip>
  You don't need to write rules for interruptions, silence, or language switching — the platform handles those automatically. Focus your prompt on your business logic.
</Tip>

## Actions

Actions are triggered by tags in the agent's reply:

* `[SEND_SMS: message]`
* `[TRANSFER: number]`
* `[END_CALL]`

Your prompt decides **when** an action should happen. The platform handles execution. See [Actions](/actions/overview).

## Define behaviour, not assumptions

Always define how the agent should behave in key situations:

* The caller agrees, declines, or changes their mind
* Requests to speak to a human
* Asks for information not in the prompt
* Confusion or missing details
* Frustration or urgency
* Off-topic conversation

Write it explicitly. Do not assume.

## Communication style

Define tone and response style simply.

> Friendly, concise, and professional.

Avoid long descriptions of tone rules. Minimal and consistent works best.

## Inbound vs outbound

<Tabs>
  <Tab title="Inbound">
    Inbound agents handle incoming calls. Your prompt should define:

    * Greeting behaviour
    * Common caller intents
    * How to respond to each intent
    * Escalation or transfer rules
  </Tab>

  <Tab title="Outbound">
    Outbound agents initiate calls. Your prompt must define:

    * A clear call purpose
    * The opening line (who is calling and why)
    * The expected outcome of the call
    * When and how the call should end
  </Tab>
</Tabs>

<Warning>
  Do not reuse inbound prompts for outbound agents. Inbound agents respond to the caller; outbound agents lead the conversation with a clear purpose.
</Warning>

## Checklist before going live

* [ ] Agent role is clearly defined
* [ ] Call purpose or intent is clearly defined
* [ ] Key scenarios are covered (yes, no, escalation, confusion)
* [ ] Multi-step flows are explicitly written
* [ ] SMS / transfer / end-call rules are included where needed
* [ ] Inbound or outbound behaviour is correctly set
* [ ] Call ending conditions are clearly defined
* [ ] Prompt is focused and concise

## Related

* [Agents](/concepts/agents)
* [Actions](/actions/overview)
* [Variables](/concepts/variables)