Astreus

Plugin

Extensible tool system with JSON schema validation and automatic function calling Learn the setup patterns, APIs, and practical examples needed to build...

Extensible tool system with JSON schema validation and automatic function calling

Overview

Plugins extend agent capabilities by providing tools that can be called during conversations. The plugin system is built around a decorator pattern that enhances agents with tool execution capabilities. It provides automatic parameter validation, error handling, and seamless LLM integration with function calling.

Built-in Tools

Astreus comes with several built-in tools available to all agents:

Knowledge Tools

  • search_knowledge: Search through the agent's knowledge base for relevant information
    • query (string, required): Search query
    • limit (number, optional): Maximum results (default: 5)
    • threshold (number, optional): Similarity threshold (default: 0.7)

Vision Tools

  • analyze_image: General image analysis with custom prompts
  • describe_image: Generate accessibility-friendly descriptions
  • extract_text_from_image: OCR capabilities for text extraction

Creating Custom Plugins

1

Define Your Tool

Create a tool definition with handler function:

import { ToolDefinition, ToolContext, ToolParameterValue } from '@astreus-ai/astreus';

const weatherTool: ToolDefinition = {
  name: 'get_weather',
  description: 'Get current weather information for a location',
  parameters: {
    location: {
      name: 'location',
      type: 'string',
      description: 'City name or location',
      required: true
    },
    units: {
      name: 'units',
      type: 'string',
      description: 'Temperature units (celsius or fahrenheit)',
      required: false
    }
  },
  handler: async (params: Record<string, ToolParameterValue>, context?: ToolContext) => {
    try {
      // Your tool implementation
      const weather = await fetchWeather(params.location as string, params.units as string);

      return {
        success: true,
        data: {
          temperature: weather.temp,
          conditions: weather.conditions,
          location: params.location
        }
      };
    } catch (error) {
      return {
        success: false,
        error: error instanceof Error ? error.message : 'Unknown error'
      };
    }
  }
};
2

Create the Plugin

Bundle your tools into a plugin:

import { Plugin, ToolParameterValue } from '@astreus-ai/astreus';

const weatherPlugin: Plugin = {
  name: 'weather-plugin',
  version: '1.0.0',
  description: 'Weather information tools',
  tools: [weatherTool],
  
  // Optional: Plugin initialization
  initialize: async (config?: Record<string, ToolParameterValue>) => {
    console.log('Weather plugin initialized');
  },
  
  // Optional: Plugin cleanup
  cleanup: async () => {
    console.log('Weather plugin cleaned up');
  }
};
3

Register with Agent

Register your plugin with an agent:

import { Agent } from '@astreus-ai/astreus';

const agent = await Agent.create({
  name: 'WeatherAgent',
  model: 'gpt-4o'
});

// Register the plugin
await agent.registerPlugin(weatherPlugin);

Tool Parameter Types

The plugin system supports comprehensive parameter validation:

// Parameter type definitions
interface ToolParameter {
  name: string;              // Parameter name
  type: 'string' | 'number' | 'boolean' | 'object' | 'array';
  description: string;       // Parameter description
  required?: boolean;        // Whether parameter is required (optional, defaults to false)
  enum?: Array<string | number>;  // Allowed values (supports both string and number)
  properties?: Record<string, ToolParameter>; // For object types (nested properties)
  items?: ToolParameter;     // For array types (item type definition)
}

Parameter Examples

const advancedTool: ToolDefinition = {
  name: 'process_data',
  description: 'Process data with various options',
  parameters: {
    // String with enum values
    format: {
      name: 'format',
      type: 'string',
      description: 'Output format',
      required: true,
      enum: ['json', 'csv', 'xml']
    },
    
    // Number parameter (optional)
    limit: {
      name: 'limit',
      type: 'number',
      description: 'Maximum records to process',
      required: false
    },
    
    // Object with nested properties
    options: {
      name: 'options',
      type: 'object',
      description: 'Processing options',
      required: false,
      properties: {
        includeHeaders: {
          name: 'includeHeaders',
          type: 'boolean',
          description: 'Include column headers',
          required: false
        }
      }
    },
    
    // Array of strings
    fields: {
      name: 'fields',
      type: 'array',
      description: 'Fields to include',
      required: false,
      items: {
        name: 'field',
        type: 'string',
        description: 'Field name'
      }
    }
  },
  handler: async (params) => {
    // Tool implementation
    return { success: true, data: params };
  }
};

Using Tools in Conversations

Automatic Tool Usage

Agents with registered plugins can automatically use tools during conversations:

const agent = await Agent.create({
  name: 'AssistantAgent',
  model: 'gpt-4o'
});

await agent.registerPlugin(weatherPlugin);

// Agent can automatically call tools based on conversation
const response = await agent.ask("What's the weather like in Tokyo?");
// Agent will automatically call get_weather tool and incorporate results

console.log(response);
// "The current weather in Tokyo is 22°C with clear skies..."

Manual Tool Execution

You can also execute tools manually:

// Execute single tool
const result = await agent.executeTool({
  id: 'call-123',
  name: 'get_weather',
  parameters: {
    location: 'New York',
    units: 'celsius'
  }
});

console.log(result.result.success ? result.result.data : result.result.error);

// Execute multiple tools sequentially
const results = await Promise.all([
  agent.executeTool({ id: 'call-1', name: 'get_weather', parameters: { location: 'Tokyo' } }),
  agent.executeTool({ id: 'call-2', name: 'get_weather', parameters: { location: 'London' } })
]);

Tool-Enhanced Tasks

Use tools in structured tasks via the Task module:

const task = await agent.createTask({
  prompt: "Compare the weather in Tokyo, London, and New York",
  useTools: true
});

const result = await agent.executeTask(task.id, {
  stream: true,
  onChunk: (chunk) => {
    console.log(chunk);
  }
});

Tool Context and Metadata

Tools receive execution context with useful information:

const contextAwareTool: ToolDefinition = {
  name: 'log_action',
  description: 'Log an action with context',
  parameters: {
    action: {
      name: 'action',
      type: 'string',
      description: 'Action to log',
      required: true
    }
  },
  handler: async (params, context) => {
    // Access execution context
    console.log(`Agent ${context?.agentId} performed: ${params.action}`);
    console.log(`Task ID: ${context?.taskId}`);
    console.log(`User ID: ${context?.userId}`);
    console.log(`Metadata:`, context?.metadata);
    
    return {
      success: true,
      data: { logged: true, timestamp: new Date().toISOString() }
    };
  }
};

Response Types

Understanding tool execution responses helps you handle results and errors properly.

Tool Execution Response

Executing a tool returns a ToolCallResult with execution details:

const result = await agent.executeTool({
  id: "call-123",
  name: "get_weather",
  parameters: {
    location: "Tokyo",
    units: "celsius"
  }
});

// Response structure:
{
  id: "call-123",
  name: "get_weather",
  result: {
    success: true,
    data: {
      temperature: 22,
      conditions: "clear skies",
      location: "Tokyo",
      humidity: 65,
      wind: "5 km/h"
    }
  },
  executionTime: 250  // Execution time in milliseconds
}

Tool Execution with Error

When a tool fails, the error is included in the result:

const result = await agent.executeTool({
  id: "call-456",
  name: "get_weather",
  parameters: {
    location: "InvalidCity"
  }
});

// Response with error:
{
  id: "call-456",
  name: "get_weather",
  result: {
    success: false,
    error: "Location 'InvalidCity' not found"
  },
  executionTime: 150
}

Multiple Tool Execution Response

Executing multiple tools using Promise.all returns an array of results:

const results = await Promise.all([
  agent.executeTool({ id: "call-1", name: "get_weather", parameters: { location: "Tokyo" } }),
  agent.executeTool({ id: "call-2", name: "get_weather", parameters: { location: "London" } }),
  agent.executeTool({ id: "call-3", name: "search_knowledge", parameters: { query: "climate" } })
]);

// Response structure:
[
  {
    id: "call-1",
    name: "get_weather",
    result: {
      success: true,
      data: { temperature: 22, conditions: "clear" }
    },
    executionTime: 200
  },
  {
    id: "call-2",
    name: "get_weather",
    result: {
      success: true,
      data: { temperature: 15, conditions: "cloudy" }
    },
    executionTime: 220
  },
  {
    id: "call-3",
    name: "search_knowledge",
    result: {
      success: true,
      data: [
        { content: "Climate patterns...", similarity: 0.92 },
        { content: "Global warming...", similarity: 0.85 }
      ]
    },
    executionTime: 180
  }
]

Tool List Response

Retrieving available tools returns an array of tool definitions:

const tools = agent.getTools();

// Response structure:
[
  {
    name: "get_weather",
    description: "Get current weather information for a location",
    parameters: {
      location: {
        name: "location",
        type: "string",
        description: "City name or location",
        required: true
      },
      units: {
        name: "units",
        type: "string",
        description: "Temperature units",
        required: false
      }
    },
    handler: [Function]
  },
  {
    name: "search_knowledge",
    description: "Search through the agent's knowledge base",
    parameters: { /* ... */ },
    handler: [Function]
  }
]

Plugin List Response

Listing registered plugins:

const plugins = agent.listPlugins();

// Response structure:
[
  {
    name: "weather-plugin",
    version: "1.0.0",
    description: "Weather information tools",
    tools: [ /* ToolDefinition[] */ ],
    initialize: [Function],
    cleanup: [Function]
  },
  {
    name: "data-plugin",
    version: "2.1.0",
    description: "Data processing utilities",
    tools: [ /* ToolDefinition[] */ ]
  }
]

Last updated: May 26, 2026

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