Build a Modular AI Agent with OpenRouter

This skill helps you create a modular AI agent with:

• Standalone Agent Core - Runs independently, extensible via hooks
• OpenRouter SDK - Unified access to 300+ language models
• Optional Ink TUI - Beautiful terminal UI (separate from agent logic)

Architecture

┌─────────────────────────────────────────────────────┐
│                    Your Application                 │
├─────────────────────────────────────────────────────┤
│  ┌─────────────┐  ┌─────────────┐  ┌─────────────┐  │
│  │   Ink TUI   │  │  HTTP API   │  │   Discord   │  │
│  └──────┬──────┘  └──────┬──────┘  └──────┬──────┘  │
│         │                │                │         │
│         └────────────────┼────────────────┘         │
│                          ▼                          │
│              ┌───────────────────────┐              │
│              │      Agent Core       │              │
│              │  (hooks & lifecycle)  │              │
│              └───────────┬───────────┘              │
│                          ▼                          │
│              ┌───────────────────────┐              │
│              │    OpenRouter SDK     │              │
│              └───────────────────────┘              │
└─────────────────────────────────────────────────────┘

Prerequisites

Get an OpenRouter API key at: https://openrouter.ai/settings/keys

⚠️ Security: Never commit API keys. Use environment variables.

Project Setup

Step 1: Initialize Project

mkdir my-agent && cd my-agent
npm init -y
npm pkg set type="module"

Step 2: Install Dependencies

npm install @openrouter/sdk zod eventemitter3
npm install ink react  # Optional: only for TUI
npm install -D typescript @types/react tsx

Step 3: Create tsconfig.json

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "NodeNext",
    "moduleResolution": "NodeNext",
    "jsx": "react-jsx",
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "outDir": "dist"
  },
  "include": ["src"]
}

Step 4: Add Scripts to package.json

{
  "scripts": {
    "start": "tsx src/cli.tsx",
    "start:headless": "tsx src/headless.ts",
    "dev": "tsx watch src/cli.tsx"
  }
}

File Structure

src/
├── agent.ts        # Standalone agent core with hooks
├── tools.ts        # Tool definitions
├── cli.tsx         # Ink TUI (optional interface)
└── headless.ts     # Headless usage example

Step 1: Agent Core with Hooks

Create src/agent.ts - the standalone agent that can run anywhere:

import { OpenRouter, tool, stepCountIs } from '@openrouter/sdk';
import type { Tool, StopCondition, StreamableOutputItem } from '@openrouter/sdk';
import { EventEmitter } from 'eventemitter3';
import { z } from 'zod';

// Message types
export interface Message {
  role: 'user' | 'assistant' | 'system';
  content: string;
}

// Agent events for hooks (items-based streaming model)
export interface AgentEvents {
  'message:user': (message: Message) => void;
  'message:assistant': (message: Message) => void;
  'item:update': (item: StreamableOutputItem) => void;  // Items emitted with same ID, replace by ID
  'stream:start': () => void;
  'stream:delta': (delta: string, accumulated: string) => void;
  'stream:end': (fullText: string) => void;
  'tool:call': (name: string, args: unknown) => void;
  'tool:result': (name: string, result: unknown) => void;
  'reasoning:update': (text: string) => void;  // Extended thinking content
  'error': (error: Error) => void;
  'thinking:start': () => void;
  'thinking:end': () => void;
}


// Agent configuration
export interface AgentConfig {
  apiKey: string;
  model?: string;
  instructions?: string;
  tools?: Tool<z.ZodTypeAny, z.ZodTypeAny>[];
  maxSteps?: number;
}

// The Agent class - runs independently of any UI
export class Agent extends EventEmitter<AgentEvents> {
  private client: OpenRouter;
  private messages: Message[] = [];
  private config: Required<Omit<AgentConfig, 'apiKey'>> & { apiKey: string };

  constructor(config: AgentConfig) {
    super();
    this.client = new OpenRouter({ apiKey: config.apiKey });
    this.config = {
      apiKey: config.apiKey,
      model: config.model ?? 'openrouter/auto',
      instructions: config.instructions ?? 'You are a helpful assistant.',
      tools: config.tools ?? [],
      maxSteps: config.maxSteps ?? 5,
    };
  }

  // Get conversation history
  getMessages(): Message[] {
    return [...this.messages];
  }

  // Clear conversation
  clearHistory(): void {
    this.messages = [];
  }

  // Add a system message
  setInstructions(instructions: string): void