@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 extend BaseTool with a call() method
• The difference between stateless and stateful tools
• How to define input schemas with Zod on the @Tool decorator
• How to use NestJS dependency injection in tools
• How to wire tools into workflows using @InjectTool()
• How to use wait: true on transitions for manual triggers
• How to return output from a workflow

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. It extends BaseTool and implements a call() method:

import { BaseTool, Tool, ToolResult } from '@loopstack/common';

@Tool({
  uiConfig: {
    description: 'Counter tool.',
  },
})
export class CounterTool extends BaseTool {
  count: number = 0;

  call(_args?: object): Promise<ToolResult<number>> {
    this.count++;
    return Promise.resolve({ data: this.count });
  }
}

The count property persists across calls within the same workflow execution, so each call increments the counter.

2. Tool with Input Schema and Dependency Injection

A tool that accepts typed arguments via a Zod schema and uses NestJS dependency injection for services:

import { Inject } from '@nestjs/common';
import { z } from 'zod';
import { BaseTool, Tool, ToolResult } from '@loopstack/common';
import { MathService } from '../services/math.service';

const MathSumSchema = z
  .object({
    a: z.number(),
    b: z.number(),
  })
  .strict();

type MathSumArgs = z.infer<typeof MathSumSchema>;

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

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

The schema option on @Tool validates incoming arguments. 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 extends BaseWorkflow<TArgs> with a typed argument object. The schema is defined in the @Workflow decorator:

@Workflow({
  uiConfig: __dirname + '/custom-tool-example.ui.yaml',
  schema: z
    .object({
      a: z.number().default(1),
      b: z.number().default(2),
    })
    .strict(),
})
export class CustomToolExampleWorkflow extends BaseWorkflow<{ a: number; b: number }> {
  @InjectTool() private counterTool: CounterTool;
  @InjectTool() private createChatMessage: CreateChatMessage;
  @InjectTool() private mathTool: MathSumTool;

  total?: number;
}

Key Concepts

1. Calling Custom Tools

Call tools via this.tool.call(args) inside transition methods. Store the result as an instance property:

@Initial({ to: 'waiting_for_user' })
async calculate(args: { a: number; b: number }) {
  const calcResult = await this.mathTool.call({ a: args.a, b: args.b });
  this.total = calcResult.data as number;

  await this.createChatMessage.call({
    role: 'assistant',
    content: `Tool calculation result:\n${args.a} + ${args.b} = ${this.total}`,
  });

  await this.createChatMessage.call({
    role: 'assistant',
    content: `Alternatively, using workflow method:\n${args.a} + ${args.b} = ${this.sum(args.a, args.b)}`,
  });
}

2. Stateful Tool Behavior

The counter tool increments on each call, demonstrating that tool state persists within a workflow execution:

const c1 = await this.counterTool.call({});
const c2 = await this.counterTool.call({});
const c3 = await this.counterTool.call({});

await this.createChatMessage.call({
  role: 'assistant',
  content: `Counter before pause: ${c1.data}, ${c2.data}, ${c3.data}\n\nPress Next to continue...`,
});

3. Wait Transitions

Use wait: true on a transition to pause the workflow until it is manually triggered (e.g., by user input):

@Transition({ from: 'waiting_for_user', to: 'resumed', wait: true })
async userContinue() {}

The workflow pauses at the waiting_for_user state until an external signal triggers the userContinue transition.

4. Workflow Output

A @Final method can return data as the workflow output:

@Final({ from: 'resumed' })
async continueCount(): Promise<{ total: number | undefined }> {
  const c4 = await this.counterTool.call({});
  const c5 = await this.counterTool.call({});
  const c6 = await this.counterTool.call({});

  await this.createChatMessage.call({
    role: 'assistant',
    content: `Counter after resume: ${c4.data}, ${c5.data}, ${c6.data}\n\nIf state persisted, this should be 4, 5, 6.`,
  });

  return { total: this.total };
}

After resuming, the counter continues from where it left off (4, 5, 6), demonstrating that tool state survives a wait pause.

5. Private Helper Methods

Define private methods for reusable logic within the workflow:

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

Complete Workflow

import { z } from 'zod';
import { BaseWorkflow, Final, Initial, InjectTool, Transition, Workflow } from '@loopstack/common';
import { CreateChatMessage } from '@loopstack/create-chat-message-tool';
import { MathSumTool } from '../tools';
import { CounterTool } from '../tools';

@Workflow({
  uiConfig: __dirname + '/custom-tool-example.ui.yaml',
  schema: z
    .object({
      a: z.number().default(1),
      b: z.number().default(2),
    })
    .strict(),
})
export class CustomToolExampleWorkflow extends BaseWorkflow<{ a: number; b: number }> {
  @InjectTool() private counterTool: CounterTool;
  @InjectTool() private createChatMessage: CreateChatMessage;
  @InjectTool() private mathTool: MathSumTool;

  total?: number;

  @Initial({ to: 'waiting_for_user' })
  async calculate(args: { a: number; b: number }) {
    const calcResult = await this.mathTool.call({ a: args.a, b: args.b });
    this.total = calcResult.data as number;

    await this.createChatMessage.call({
      role: 'assistant',
      content: `Tool calculation result:\n${args.a} + ${args.b} = ${this.total}`,
    });

    await this.createChatMessage.call({
      role: 'assistant',
      content: `Alternatively, using workflow method:\n${args.a} + ${args.b} = ${this.sum(args.a, args.b)}`,
    });

    const c1 = await this.counterTool.call({});
    const c2 = await this.counterTool.call({});
    const c3 = await this.counterTool.call({});

    await this.createChatMessage.call({
      role: 'assistant',
      content: `Counter before pause: ${c1.data}, ${c2.data}, ${c3.data}\n\nPress Next to continue...`,
    });
  }

  @Transition({ from: 'waiting_for_user', to: 'resumed', wait: true })
  async userContinue() {}

  @Final({ from: 'resumed' })
  async continueCount(): Promise<{ total: number | undefined }> {
    const c4 = await this.counterTool.call({});
    const c5 = await this.counterTool.call({});
    const c6 = await this.counterTool.call({});

    await this.createChatMessage.call({
      role: 'assistant',
      content: `Counter after resume: ${c4.data}, ${c5.data}, ${c6.data}\n\nIf state persisted, this should be 4, 5, 6.`,
    });

    return { total: this.total };
  }

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

Dependencies

This workflow uses the following Loopstack modules:

• @loopstack/common - Base classes, decorators, and tool injection
• @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