@loopstack/custom-tool-example-module

@loopstack/custom-tool-example-module

A module for the Loopstack AI automation framework.

This module provides a complete example demonstrating how to implement and use custom tools in a Loopstack workflow.

Overview

Custom tools are the building blocks of Loopstack automations. This module serves as a hands-on reference for developers learning how to extend Loopstack with their own functionality.

By exploring this example, you'll understand:

• How to create tools that perform specific tasks within workflows
• The difference between stateless and stateful tools
• How to use dependency injection to keep tools modular and testable
• How to wire tools into workflows using YAML configuration
• How to define workflow input, state, and output
• How to structure and export a reusable module

This is a great starting point before building your own custom tools.

Installation

See SETUP.md for installation and setup instructions.

How It Works

Creating Custom Tools

1. Stateful Tool (Counter)

A simple tool that maintains internal state across calls using the @Tool decorator and ToolInterface:

@Tool({
  config: {
    description: 'Counter tool.',
  },
})
export class CounterTool implements ToolInterface {
  count: number = 0;

  async execute(): Promise<ToolResult> {
    this.count++;
    return Promise.resolve({
      data: this.count,
    });
  }
}

2. Tool with Input Schema and Dependency Injection

A tool that accepts typed arguments via @Input and uses NestJS dependency injection for services:

@Tool({
  config: {
    description: 'Math tool calculating the sum of two arguments by using an injected service.',
  },
})
export class MathSumTool implements ToolInterface {
  @Inject()
  private mathService: MathService;

  @Input({
    schema: z
      .object({
        a: z.number(),
        b: z.number(),
      })
      .strict(),
  })
  args: MathSumArgs;

  async execute(args: MathSumArgs): Promise<ToolResult<number>> {
    const sum = this.mathService.sum(args.a, args.b);
    return Promise.resolve({
      data: sum,
    });
  }
}

The injected MathService is a standard NestJS injectable:

@Injectable()
export class MathService {
  public sum(a: number, b: number) {
    return a + b;
  }
}

Workflow Class

The workflow class declares input, state, output, tools, and helpers:

@Workflow({
  uiConfig: __dirname + '/custom-tool-example.ui.yaml',
})
export class CustomToolExampleWorkflow {
  @InjectTool() private counterTool: CounterTool;
  @InjectTool() private createChatMessage: CreateChatMessage;
  @InjectTool() private mathTool: MathSumTool;

  @Input({
    schema: z
      .object({
        a: z.number().default(1),
        b: z.number().default(2),
      })
      .strict(),
  })
  args: { a: number; b: number };

  @State({
    schema: z
      .object({
        total: z.number().optional(),
        count1: z.number().optional(),
        count2: z.number().optional(),
        count3: z.number().optional(),
      })
      .strict(),
  })
  state: { total?: number; count1?: number; count2?: number; count3?: number };

  @Output()
  result() {
    return { total: this.state.total };
  }

  @DefineHelper()
  sum(a: number, b: number) {
    return a + b;
  }
}

Workflow YAML

Using Custom Tools

Call custom tools and save their results to state using assign:

- id: calculation
  tool: mathTool
  args:
    a: ${{ args.a }}
    b: ${{ args.b }}
  assign:
    total: ${{ result.data }}

Accessing State and Arguments

Reference workflow arguments with args.<name> and state with state.<name>:

- tool: createChatMessage
  args:
    role: 'assistant'
    content: |
      Tool calculation result:
      {{ args.a }} + {{ args.b }} = {{ state.total }}

Using Helper Functions

Call workflow helpers in templates:

- tool: createChatMessage
  args:
    role: 'assistant'
    content: |
      Alternatively, using workflow getter function:
      {{ args.a }} + {{ args.b }} = {{ sum args.a args.b }}

Stateful Tool Behavior

The counter tool increments on each call, demonstrating stateful tools:

- id: count1
  tool: counterTool
  assign:
    count1: ${{ result.data }}
- id: count2
  tool: counterTool
  assign:
    count2: ${{ result.data }}
- id: count3
  tool: counterTool
  assign:
    count3: ${{ result.data }}
- tool: createChatMessage
  args:
    role: 'assistant'
    content: |
      Counter tool should count:

      {{ state.count1 }}, {{ state.count2 }}, {{ state.count3 }}

Workflow Output

The @Output() decorator defines the data returned when the workflow completes:

@Output()
result() {
  return { total: this.state.total };
}

Dependencies

This workflow uses the following Loopstack modules:

• @loopstack/core - Core framework functionality
• @loopstack/create-chat-message-tool - Provides CreateChatMessage tool

About

Author: Jakob Klippel

License: Apache-2.0

Additional Resources

• Loopstack Documentation
• Getting Started with Loopstack
• Find more Loopstack examples in the Loopstack Registry