Patterns Factory / Registry Pattern See in Code Tour

Factory Pattern

A central tool registry that produces Tool instances on demand — enabling dynamic loading and MCP tool injection.

Factory Pattern — Architecture Diagram

graph TD
    A[Tool Registry] --> B[findToolByName]
    B --> C{Built-in?}
    C -->|Yes| D[Return Built-in Tool]
    C -->|No| E{MCP Tool?}
    E -->|Yes| F[Wrap in MCPTool adapter]
    E -->|No| G[Return undefined]
    D --> H[StreamingToolExecutor]
    F --> H

Mermaid diagram definition

Deep Dive

The tool registry in src/tools.ts is a Factory: given a tool name from Claude's response, it produces the correct Tool object. This decouples the query engine (which needs to execute tools) from the tool implementations.

🔑Key Insight

MCP tools are wrapped in a `MCPTool` adapter at registration time. The factory produces the same `Tool` interface regardless of whether the underlying tool is built-in TypeScript code or a remote MCP server.

ℹ️Info

`findToolByName()` supports aliases: a tool can have multiple names (for backwards compatibility when renamed). The registry resolves any alias to the canonical implementation.

KEY TAKEAWAYS

→Registry pattern centralizes object creation logic
→Alias support enables backwards-compatible tool renaming
→MCP tools are wrapped at registration, not at call time
→The factory is the only place tool enumeration happens

Source Code

findToolByName() and toolMatchesName() — the factory lookup functions.

 */
export function toolMatchesName(
  tool: { name: string; aliases?: string[] },
  name: string,
): boolean {
  return tool.name === name || (tool.aliases?.includes(name) ?? false)
}

/**
 * Finds a tool by name or alias from a list of tools.
 */
export function findToolByName(tools: Tools, name: string): Tool | undefined {
  return tools.find(t => toolMatchesName(t, name))
}

export type Tool<
  Input extends AnyObject = AnyObject,
  Output = unknown,
  P extends ToolProgressData = ToolProgressData,

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