Tool

# Tool

The atomic callable unit that an agent can invoke to perform work.

## Category
Tool

## Context
Building any capability that agents can use.

## Problem
Agents need well-defined units of functionality they can discover, understand, and invoke.

## Solution
A Tool is the fundamental building block: a named, typed function with:
- **Name**: Reflects intent (verb_noun pattern)
- **Description**: LLM-optimized explanation
- **Parameters**: Typed inputs with constraints
- **Return type**: Structured output
- **Side effects**: Documented state changes

## Example (Python)
```python
@tool
def send_email(
    recipient: str,
    subject: str,
    body: str
) -> SendResult:
    """Send an email to a recipient."""
    # Tool implementation
```
## Example (TypeScript)
```typescript
const sendEmail = tool({
  name: "send_email",
  description: "Send an email to a recipient",
  parameters: z.object({
    recipient: z.string(),
    subject: z.string(),
    body: z.string()
  }),
  execute: async (params) => { /* ... */ }
});
```

## Considerations
- One tool = one clear responsibility
- Names should be verbs reflecting the action
- Document all side effects explicitly

## Related Patterns
- query-tool
- command-tool
- tool-description

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