add-tool

name	add-tool
description	Add a new built-in tool to Lulu. Use when extending Lulu with a new capability like file editing, git operations, or web search.

Skill: Add Built-in Tool

Add a new tool to Lulu's built-in tool set.

Context

• Tools defined in src/agent/tools.ts
• BUILTIN_TOOLS: ToolDef[] — declarative schema array
• executeToolImpl — switch-based dispatch
• Types in src/types.ts (ToolDef, ToolCall, ToolResult)

Steps

1. Define the schema — add entry to BUILTIN_TOOLS array:

{
  name: "my_tool",
  description: "What this tool does. Keep it clear for the LLM.",
  input_schema: {
    type: "object",
    properties: {
      param1: { type: "string", description: "Description of param1" },
      param2: { type: "integer", description: "Optional param" },
    },
    required: ["param1"],
  },
}

2. Add implementation — add case to executeToolImpl switch:

case "my_tool": {
  const p1 = call.input.param1 as string;
  const p2 = (call.input.param2 as number) ?? default;
  // ... tool logic ...
  return `Result: ${output}`;
}

3. Add permission gate if destructive — check env var at top:

if (process.env.LULU_ALLOW_MY_TOOL !== "true") {
  throw new Error("my_tool is disabled. Set LULU_ALLOW_MY_TOOL=true.");
}

4. Build & test:

npm run build && node dist/index.js "use my_tool to do something"

Tool Design Rules

• Return plain text strings — the LLM reads the output
• Report errors via return string (not throw) when possible
• Use throw only for hard failures (caught by executeTool)
• Keep tools idempotent where possible