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

# Custom Functions in System Prompts

> Use your own functions to build dynamic system prompts that include real-time data and custom logic

Pass a function to `system_prompt` that builds the prompt using your custom functions:

```python theme={"dark"}
from datetime import datetime
from timbal import Agent
from timbal.state import get_run_context

def get_system_prompt() -> str:
    span = get_run_context().current_span()
    current_time = datetime.now().strftime("%Y-%m-%d %H:%M:%S")
    user_id = span.input.get("user_id", "unknown")
    
    return f"""You are a helpful assistant.
Current time: {current_time}
User: {user_id}"""

agent = Agent(
    name="TimeAwareAgent",
    model="openai/gpt-4o-mini",
    system_prompt=get_system_prompt
)
```

Your function is executed each time the agent runs, ensuring the system prompt always contains up-to-date information.

## Key Features

* **Custom Functions**: Define your own functions to fetch and format data
* **Automatic Execution**: Your function is called each time the agent runs
* **Access Runtime Context**: Use `get_run_context()` to access current execution data and user inputs
* **Full Control**: Build the system prompt dynamically with any logic you need
* **Real-time Data**: Perfect for integrating APIs, databases, or any dynamic data source