Discovery Tool

# Discovery Tool

A tool that reveals available operations, schema, or capabilities.

## Category
Tool

## Context
Building tools that help agents explore what's possible.

## Problem
Agents need to understand what data exists and what operations are available before taking action.

## Solution
A Discovery Tool reveals structure:
- **list_tables()**: What data exists
- **describe_schema()**: What fields are available
- **get_capabilities()**: What operations are possible
- **who_am_i()**: Current user context

## Example (Python)
```python
@tool
def list_available_reports() -> list[ReportType]:
    """List all report types the user can generate.
    Call this first to see what's available."""
    return report_service.get_available_types(current_user)
```
## Example (TypeScript)
```typescript
const listTables = tool({
  name: "list_tables",
  description: "List database tables. Call before querying.",
  execute: async () => db.getTables()
});
```

## Considerations
- Discovery tools are essential for schema-on-read scenarios
- Return enough detail for the agent to make informed decisions
- Consider layered discovery (list → describe → sample)

## Related Patterns
- schema-explorer
- identity-anchor
- tool-registry

---
Source: https://arcade.dev/patterns/discovery-tool