Custom Tools

View the complete sample on GitHub

Overview

In this example we will guide you through creating custom tools using the Strands Agents tool() function. We will build a personal assistant that connects with a local SQLite database to manage appointments.

Feature	Description
Custom tools created	create_appointment, list_appointments, update_appointment
Agent Structure	Single agent architecture

Prerequisites

• Node.js 22 or later (the version @strands-agents/sdk supports)
• AWS account with Amazon Bedrock access
• Basic TypeScript knowledge

Running the Example

cd typescript/01-learn/02-custom-tools
npm install
npx tsx src/index.ts

Project Structure

src/
├── database/
│   └── AppointmentDatabase.ts    # SQLite data access layer
├── tools/
│   └── AppointmentTools.ts       # Tool definitions factory
└── index.ts                      # Main entry point

Key Concepts

Class-Based Tool Organization

Tools are organized using a factory class pattern that encapsulates tool creation and database dependencies:

export class AppointmentTools {
  constructor(private database: AppointmentDatabase) { }

  getCreateAppointmentTool() {
    return tool({
      name: "create_appointment",
      description: "Create a new personal appointment...",
      inputSchema: z.object({ date, location, title, description }),
      callback: (input) => {
        const id = this.database.createAppointment(...);
        return `Appointment created with ID: ${id}`;
      }
    });
  }

  getAllTools() {
    return [
      this.getCreateAppointmentTool(),
      this.getListAppointmentsTool(),
      this.getUpdateAppointmentTool()
    ];
  }
}

Database Integration

The AppointmentDatabase class uses better-sqlite3 to store appointment information:

export class AppointmentDatabase {
  constructor(databasePath: string = "appointments.db") {
    this.db = new Database(databasePath);
    this.initializeTables();
  }

  createAppointment(date, location, title, description): string
  listAppointments(): Appointment[]
  updateAppointment(id, updates): number
}

Agent Configuration

const agent = new Agent({
  model: new BedrockModel({
    modelId: "us.anthropic.claude-haiku-4-5-20251001-v1:0",
  }),
  systemPrompt: "You are a helpful personal assistant...",
  tools
});

Additional Resources

• Strands Agents Documentation