Custom Configuration Data for NeMo Guardrails

The custom_data field in config.yml allows you to pass additional configuration to your custom initialization code and actions.

Defining Custom Data

Add a custom_data section to your config.yml:

models:
  - type: main
    engine: openai
    model: gpt-4
custom_data:
  api_endpoint: "https://api.example.com"
  max_retries: 3
  timeout_seconds: 30
  feature_flags:
    enable_caching: true
    debug_mode: false

Accessing in config.py

Access custom data in your init function:

from nemoguardrails import LLMRails
def init(app: LLMRails):
    # Access custom_data from the configuration
    custom_data = app.config.custom_data
    # Get individual values
    api_endpoint = custom_data.get("api_endpoint")
    max_retries = custom_data.get("max_retries", 3)  # with default
    # Access nested values
    feature_flags = custom_data.get("feature_flags", {})
    enable_caching = feature_flags.get("enable_caching", False)
    # Load sensitive values from environment variables
    import os
    api_key = os.environ.get("API_KEY")
    # Use to configure your providers
    client = APIClient(
        endpoint=api_endpoint,
        api_key=api_key,
        max_retries=max_retries
    )
    app.register_action_param("api_client", client)

Accessing in Actions

You can also access custom data directly in actions via the config parameter:

from nemoguardrails.actions import action
@action()
async def my_action(config=None):
    """Access custom_data via the config parameter."""
    custom_data = config.custom_data
    timeout = custom_data.get("timeout_seconds", 30)
    # Use the configuration
    return await do_something(timeout=timeout)

Sensitive Configuration

For sensitive values like API keys, use the api_key_env_var field on model configurations or load environment variables in your init() function:

config.py:

import os
from nemoguardrails import LLMRails
def init(app: LLMRails):
    custom_data = app.config.custom_data
    api_key = os.environ.get("API_KEY")
    db_url = os.environ.get("DATABASE_URL", "postgresql://localhost/myapp")
    client = APIClient(
        endpoint=custom_data.get("api_endpoint"),
        api_key=api_key,
    )
    app.register_action_param("api_client", client)

The custom_data field in config.yml uses standard YAML parsing and does not support inline environment variable substitution (e.g., ${VAR}). Load sensitive values from environment variables in your init() function instead.

Best Practices

Use environment variables for secrets: Never hardcode API keys or passwords.
Provide defaults: Use .get("key", default) for optional values.
Document your custom_data schema: Add comments in config.yml explaining expected fields.
Validate configuration: Check required fields in init() and raise clear errors.

def init(app: LLMRails):
    custom_data = app.config.custom_data
    # Validate required fields
    required_fields = ["api_endpoint", "api_key"]
    missing = [f for f in required_fields if not custom_data.get(f)]
    if missing:
        raise ValueError(f"Missing required custom_data fields: {missing}")