> ## Documentation Index > Fetch the complete documentation index at: https://docs.tryhamsa.com/llms.txt > Use this file to discover all available pages before exploring further. # Writing Effective Prompts > How to write the preamble (system prompt) for your single prompt agent ## Overview The **preamble** is the system prompt that defines your agent's identity, behavior, and task. Everything the agent does during a call is guided by this prompt. ## Recommended Structure A well-structured preamble typically covers these sections: ### 1. Identity & Role Define who the agent is and what it represents. ``` You are Alex, a customer support specialist at Acme Corp. You help customers with product inquiries, order tracking, and technical support. ``` ### 2. Personality & Tone Set the conversation style. ``` Speak in a warm, friendly, and patient manner. Keep responses concise. ``` ### 3. Response Guidelines Specify how the agent should format and structure its responses. ``` - Keep responses under 30 seconds of speech - Ask one question at a time - Confirm understanding before proceeding - If you don't know something, say so honestly ``` ### 4. Task & Goals Define what the agent should accomplish, ideally as numbered steps. ``` Your primary task is to schedule appointments. Process: 1. Greet the caller 2. Collect: full name, phone number, preferred date and time 3. Check availability using the check_availability tool 4. Confirm the appointment details 5. Provide a confirmation number ``` ### 5. Guardrails Set clear boundaries for what the agent should not do. ``` Do NOT: - Make promises you cannot keep - Discuss competitor products - Process payments or collect card details - Continue if the user is abusive ``` ### 6. Edge Case Handling Prepare for difficult scenarios. ``` If asked something outside your knowledge: - Be honest: "I don't have that information available" - Offer alternatives: "I can transfer you to someone who can help" ``` ## Using Variables You can reference system variables and custom variables in your prompt using `{{variable_name}}` syntax. **System variables** (always available): | Variable | Description | | --------------------------- | ------------------------------- | | `{{agent_name}}` | Name of the current agent | | `{{agent_id}}` | Unique identifier for the agent | | `{{agent_number}}` | Agent's phone number | | `{{current_time}}` | Current time (HH:MM) | | `{{current_date}}` | Current date (YYYY-MM-DD) | | `{{current_datetime}}` | Date and time in ISO format | | `{{current_day}}` | Day of the month (1–31) | | `{{current_month}}` | Month (1–12) | | `{{current_year}}` | Year (YYYY) | | `{{current_weekday}}` | Day of the week | | `{{current_timestamp}}` | Timestamp in milliseconds | | `{{call_id}}` | Unique call identifier | | `{{call_type}}` | Type of call | | `{{call_start_time}}` | When the call began | | `{{direction}}` | `inbound` or `outbound` | | `{{user_number}}` | Caller's phone number | | `{{user_number_area_code}}` | Caller's area code | For dynamic business-specific data (e.g., working hours, customer info), use **custom variables** passed as `params` when initiating the call. See [Variable System](/agents/variables/introduction) for details. ### Jinja2 Templates Beyond simple substitution, prompts support full **Jinja2** template syntax — conditionals, filters, and expressions are all available. ``` {% if direction == "outbound" %} Hi {{customer_name}}, this is {{agent_name}} from Acme Corporation. {% else %} Thank you for calling Acme Corporation. I'm {{agent_name}}. {% endif %} ``` ``` Welcome{% if customer_name %}, {{customer_name}}{% endif %}! Your balance is {{balance | default("unavailable")}}. ``` Templates are processed server-side before the prompt reaches the LLM. See the [Jinja2 Template Designer Documentation](https://jinja.palletsprojects.com/en/stable/templates/) for the full syntax reference. **Example:** ```markdown theme={null} You are {{agent_name}}. Today is {{current_date}} and the time is {{current_time}}. The caller's number is {{user_number}}. Working hours: {{working_hours}} ``` ## Prompt Settings Below the prompt editor, two settings control how your prompt is processed: **Enhanced Turn Taking** — Enables better numeral capturing and backchannel detection for more natural conversations. Default: Off. **Prompt Enhancer** — Applies automatic enhancements to your prompt before it reaches the LLM: | Option | Description | | ------------------- | ------------------------------------------ | | **Disabled** | Your prompt is used as-is | | **Basic** (default) | Stable, model-agnostic prompt enhancements | | **Advanced** | Model-aware prompts with live context | ## Tool Integration When your agent uses tools, include clear instructions for when and how to use them: ```markdown theme={null} To check product availability: 1. Ask for the product name or SKU 2. Use the check_inventory tool 3. Based on results: - In stock: "We have that available. Would you like to place an order?" - Out of stock: "That's currently out of stock." - Discontinued: "That product has been discontinued. Can I suggest an alternative?" ``` ## Common Mistakes **Too vague:** ``` You are a helpful assistant. Answer questions. ``` **Better:** ``` You are a customer support specialist for Acme Corp. Help customers with product questions, order tracking, and returns. Use the knowledge base for product details. ``` *** **Conflicting instructions:** ``` Be extremely brief. Provide detailed, comprehensive answers with lots of context. ``` **Better:** ``` Give concise answers (2–3 sentences). If the customer wants more detail, offer to elaborate: "Would you like me to explain that further?" ``` ## Next Steps Configure voice and language options Set up response timing and interaction controls Enable smart features like gender detection and smart call end Add reference materials for your agent