<instructions>
Get the entities for specified metrics using MetricFlow CLI

Entities are real-world concepts in a business such as customers,
transactions, and ad campaigns. Analysis is often focused around
specific entities, such as customer churn or
annual recurring revenue modeling.

This tool executes the `mf list entities --json` command locally
with optional metric filtering to return available entities.
</instructions>

<parameters>
metrics: Optional list of metric names to get entities for.
        If not provided, returns entities for all metrics.
</parameters>

<examples>
- "What entities are available for the customer_lifetime_value metric?"
- "Show me all business entities in our data model"
- "What are the main subject areas for analysis?"
</examples>

<output>
Returns JSON containing entity definitions including:
- Entity names
- Data types
- Descriptions
- Primary keys
- Relationships to other entities
</output> 