Smart Defaults

# Smart Defaults

Reduce required parameters by providing sensible defaults.

## Category
Tool Interface

## Context
Designing tool signatures.

## Problem
Too many required parameters increases cognitive load and error potential.

## Solution
Provide intelligent defaults:
- **Context-aware**: Use current user, time, etc.
- **Common case**: Default to most frequent value
- **Documented**: Explain what default means
- **Overridable**: Allow explicit override

## Example (Python)
```python
@tool
def search_emails(
    query: str,
    folder: str = "inbox",           # Common case
    max_results: int = 20,           # Reasonable limit
    include_attachments: bool = False # Performance default
) -> list[Email]:
    """Search emails. Defaults to inbox, 20 results."""
```
## Example (TypeScript)
```typescript
const searchEmails = tool({
  parameters: z.object({
    query: z.string(),
    folder: z.string().default("inbox"),
    maxResults: z.number().default(20),
    includeAttachments: z.boolean().default(false)
  })
});
```

## Considerations
- Document defaults in the description
- Use context (current user) when available
- Don't default destructive options to true
- Proactively select sensible defaults during runtime. For example, in a `create_task` tool, when the upstream API requires a project ID, we can check whether the user has a default project set or only one existing project, and set its ID by default. This way, the `project_id` parameter can be optional and set to `null` in the tool interface.

## Related Patterns
- tool-description
- constrained-input
- identity-anchor

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Source: https://arcade.dev/patterns/smart-defaults