> ## Documentation Index
> Fetch the complete documentation index at: https://0g.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Development Guide

> Guide for developing and extending the MCP 0G Server

# Development Guide

This guide covers how to develop, extend, and contribute to the MCP 0G Server.

## Development Setup

### Prerequisites

* Node.js 18.0 or higher
* TypeScript 4.9 or higher
* Git for version control
* Code editor (VS Code recommended)

### Local Development

1. **Clone Repository**

   ```bash theme={null}
   git clone https://github.com/0gfoundation/mcp-0g.git
   cd mcp-0g
   ```

2. **Install Dependencies**

   ```bash theme={null}
   npm install
   ```

3. **Environment Setup**

   ```bash theme={null}
   cp .env.example .env
   # Edit .env with your configuration
   ```

4. **Development Mode**

   ```bash theme={null}
   npm run dev
   ```

   This starts the server with auto-reload on file changes.

### Project Structure

```
mcp-0g/
├── src/                    # Source code
│   ├── tools/             # MCP tool implementations
│   ├── services/          # Business logic services
│   ├── utils/             # Utility functions
│   ├── types/             # TypeScript type definitions
│   └── index.ts           # Main server entry point
├── docs/                  # Documentation
├── examples/              # Usage examples
├── tests/                 # Test files
├── dist/                  # Compiled JavaScript
└── package.json           # Project configuration
```

## Architecture Overview

### Core Components

#### MCP Server

The main server implements the Model Context Protocol specification:

```typescript theme={null}
// src/index.ts
import { Server } from '@modelcontextprotocol/sdk/server/index.js';
import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js';

const server = new Server({
  name: "0g-mcp-server",
  version: "1.0.0"
}, {
  capabilities: {
    tools: {}
  }
});
```

#### Tool Registry

Tools are registered with the MCP server:

```typescript theme={null}
// Tool registration
server.setRequestHandler(ListToolsRequestSchema, async () => {
  return {
    tools: [
      {
        name: "get_chain_info",
        description: "Get 0G chain information",
        inputSchema: {
          type: "object",
          properties: {}
        }
      }
      // ... more tools
    ]
  };
});
```

#### Service Layer

Business logic is organized into services:

```typescript theme={null}
// src/services/BlockchainService.ts
export class BlockchainService {
  constructor(private provider: ethers.Provider) {}

  async getChainInfo(): Promise<ChainInfo> {
    const network = await this.provider.getNetwork();
    const blockNumber = await this.provider.getBlockNumber();
    
    return {
      chainId: network.chainId,
      blockNumber,
      networkName: network.name
    };
  }
}
```

## Adding New Tools

### Tool Structure

Each tool follows this pattern:

```typescript theme={null}
// src/tools/ExampleTool.ts
import { z } from 'zod';

// Input validation schema
export const ExampleToolSchema = z.object({
  parameter1: z.string(),
  parameter2: z.number().optional()
});

// Tool implementation
export async function exampleTool(
  input: z.infer<typeof ExampleToolSchema>
): Promise<any> {
  // Validate input
  const validated = ExampleToolSchema.parse(input);
  
  // Business logic
  const result = await performOperation(validated);
  
  return result;
}

// Tool metadata
export const exampleToolMetadata = {
  name: "example_tool",
  description: "Example tool description",
  inputSchema: ExampleToolSchema.schema
};
```

### Registration Process

1. **Create Tool File**

   Create a new file in `src/tools/` following the naming convention.

2. **Implement Tool Logic**

   ```typescript theme={null}
   // src/tools/NewTool.ts
   import { z } from 'zod';
   import { BlockchainService } from '../services/BlockchainService.js';

   export const NewToolSchema = z.object({
     address: z.string().regex(/^0x[a-fA-F0-9]{40}$/, "Invalid address format")
   });

   export async function newTool(
     input: z.infer<typeof NewToolSchema>,
     blockchainService: BlockchainService
   ): Promise<any> {
     const { address } = NewToolSchema.parse(input);
     
     // Your logic here
     const result = await blockchainService.someOperation(address);
     
     return {
       success: true,
       data: result
     };
   }

   export const newToolMetadata = {
     name: "new_tool",
     description: "Description of what this tool does",
     inputSchema: NewToolSchema.schema
   };
   ```

3. **Register Tool**

   Add to the tool registry:

   ```typescript theme={null}
   // src/index.ts
   import { newTool, newToolMetadata } from './tools/NewTool.js';

   // Add to tools list
   const tools = [
     // ... existing tools
     newToolMetadata
   ];

   // Add to call handler
   server.setRequestHandler(CallToolRequestSchema, async (request) => {
     const { name, arguments: args } = request.params;
     
     switch (name) {
       // ... existing cases
       case "new_tool":
         return { content: [{ type: "text", text: JSON.stringify(await newTool(args, blockchainService)) }] };
       
       default:
         throw new McpError(ErrorCode.MethodNotFound, `Tool not found: ${name}`);
     }
   });
   ```

### Best Practices for Tools

#### Input Validation

Always validate inputs using Zod schemas:

```typescript theme={null}
const ToolSchema = z.object({
  address: z.string().regex(/^0x[a-fA-F0-9]{40}$/),
  amount: z.string().regex(/^\d+$/),
  gasLimit: z.number().min(21000).optional()
});
```

#### Error Handling

Implement comprehensive error handling:

```typescript theme={null}
export async function toolFunction(input: any): Promise<any> {
  try {
    const validated = ToolSchema.parse(input);
    const result = await performOperation(validated);
    return { success: true, data: result };
  } catch (error) {
    if (error instanceof z.ZodError) {
      throw new McpError(ErrorCode.InvalidParams, `Validation error: ${error.message}`);
    }
    if (error instanceof Error) {
      throw new McpError(ErrorCode.InternalError, error.message);
    }
    throw new McpError(ErrorCode.InternalError, "Unknown error occurred");
  }
}
```

#### Async Operations

Handle async operations properly:

```typescript theme={null}
export async function asyncTool(input: any): Promise<any> {
  const validated = ToolSchema.parse(input);
  
  // Use Promise.all for parallel operations
  const [balance, nonce] = await Promise.all([
    provider.getBalance(validated.address),
    provider.getTransactionCount(validated.address)
  ]);
  
  return { balance: balance.toString(), nonce };
}
```

## Service Development

### Creating Services

Services encapsulate business logic:

```typescript theme={null}
// src/services/TokenService.ts
export class TokenService {
  constructor(
    private provider: ethers.Provider,
    private signer?: ethers.Signer
  ) {}

  async getTokenMetadata(tokenAddress: string): Promise<TokenMetadata> {
    const contract = new ethers.Contract(tokenAddress, ERC20_ABI, this.provider);
    
    const [name, symbol, decimals] = await Promise.all([
      contract.name(),
      contract.symbol(),
      contract.decimals()
    ]);

    return { name, symbol, decimals };
  }

  async transferToken(
    tokenAddress: string,
    to: string,
    amount: string
  ): Promise<string> {
    if (!this.signer) {
      throw new Error("Signer required for token transfer");
    }

    const contract = new ethers.Contract(tokenAddress, ERC20_ABI, this.signer);
    const tx = await contract.transfer(to, amount);
    
    return tx.hash;
  }
}
```

### Service Integration

Integrate services with dependency injection:

```typescript theme={null}
// src/index.ts
const provider = new ethers.JsonRpcProvider(process.env.ZEROQ_RPC_URL);
const blockchainService = new BlockchainService(provider);
const tokenService = new TokenService(provider);
const walletService = new WalletService();

// Pass services to tools
server.setRequestHandler(CallToolRequestSchema, async (request) => {
  const { name, arguments: args } = request.params;
  
  switch (name) {
    case "get_token_metadata":
      return { 
        content: [{ 
          type: "text", 
          text: JSON.stringify(await getTokenMetadata(args, tokenService)) 
        }] 
      };
    // ... other cases
  }
});
```

## Testing

### Unit Tests

Write unit tests for tools and services:

```typescript theme={null}
// tests/tools/GetBalance.test.ts
import { describe, it, expect, beforeEach } from 'vitest';
import { getBalance } from '../../src/tools/GetBalance.js';
import { BlockchainService } from '../../src/services/BlockchainService.js';

describe('GetBalance Tool', () => {
  let mockService: jest.Mocked<BlockchainService>;

  beforeEach(() => {
    mockService = {
      getBalance: jest.fn()
    } as any;
  });

  it('should return balance for valid address', async () => {
    const mockBalance = '1000000000000000000'; // 1 ETH in wei
    mockService.getBalance.mockResolvedValue(mockBalance);

    const result = await getBalance(
      { address: '0x742d35Cc6634C0532925a3b8D4C9db96590c6C87' },
      mockService
    );

    expect(result.balance).toBe(mockBalance);
    expect(mockService.getBalance).toHaveBeenCalledWith('0x742d35Cc6634C0532925a3b8D4C9db96590c6C87');
  });

  it('should throw error for invalid address', async () => {
    await expect(getBalance(
      { address: 'invalid-address' },
      mockService
    )).rejects.toThrow('Invalid address format');
  });
});
```

### Integration Tests

Test complete workflows:

```typescript theme={null}
// tests/integration/WalletFlow.test.ts
import { describe, it, expect } from 'vitest';
import { createWallet, getWallet } from '../../src/tools/WalletTools.js';

describe('Wallet Integration', () => {
  it('should create and retrieve wallet', async () => {
    const walletName = 'test-wallet';
    const password = 'secure-password';

    // Create wallet
    const createResult = await createWallet({
      name: walletName,
      password
    });

    expect(createResult.success).toBe(true);
    expect(createResult.address).toMatch(/^0x[a-fA-F0-9]{40}$/);

    // Retrieve wallet
    const getResult = await getWallet({
      name: walletName
    });

    expect(getResult.name).toBe(walletName);
    expect(getResult.address).toBe(createResult.address);
  });
});
```

### Running Tests

```bash theme={null}
# Run all tests
npm test

# Run with coverage
npm run test:coverage

# Run specific test file
npm test -- GetBalance.test.ts

# Watch mode for development
npm run test:watch
```

## Configuration Management

### Environment Variables

Define configuration schema:

```typescript theme={null}
// src/config/index.ts
import { z } from 'zod';

const ConfigSchema = z.object({
  ZEROQ_RPC_URL: z.string().url(),
  RATE_LIMIT_REQUESTS: z.string().transform(Number).pipe(z.number().min(1)),
  RATE_LIMIT_WINDOW: z.string().transform(Number).pipe(z.number().min(1000)),
  LOG_LEVEL: z.enum(['debug', 'info', 'warn', 'error']).default('info')
});

export const config = ConfigSchema.parse(process.env);
```

### Feature Flags

Implement feature flags for gradual rollouts:

```typescript theme={null}
// src/config/features.ts
export const features = {
  ENABLE_CONTRACT_DEPLOYMENT: process.env.ENABLE_CONTRACT_DEPLOYMENT === 'true',
  ENABLE_BATCH_OPERATIONS: process.env.ENABLE_BATCH_OPERATIONS === 'true',
  MAX_BATCH_SIZE: parseInt(process.env.MAX_BATCH_SIZE || '10')
};
```

## Logging and Monitoring

### Structured Logging

Implement structured logging:

```typescript theme={null}
// src/utils/logger.ts
import winston from 'winston';

export const logger = winston.createLogger({
  level: process.env.LOG_LEVEL || 'info',
  format: winston.format.combine(
    winston.format.timestamp(),
    winston.format.errors({ stack: true }),
    winston.format.json()
  ),
  transports: [
    new winston.transports.Console(),
    new winston.transports.File({ filename: 'logs/mcp-server.log' })
  ]
});
```

### Metrics Collection

Add metrics for monitoring:

```typescript theme={null}
// src/utils/metrics.ts
export class Metrics {
  private static toolCallCount = new Map<string, number>();
  private static errorCount = new Map<string, number>();

  static incrementToolCall(toolName: string): void {
    const current = this.toolCallCount.get(toolName) || 0;
    this.toolCallCount.set(toolName, current + 1);
  }

  static incrementError(errorType: string): void {
    const current = this.errorCount.get(errorType) || 0;
    this.errorCount.set(errorType, current + 1);
  }

  static getMetrics(): any {
    return {
      toolCalls: Object.fromEntries(this.toolCallCount),
      errors: Object.fromEntries(this.errorCount)
    };
  }
}
```

## Security Considerations

### Input Sanitization

Always sanitize and validate inputs:

```typescript theme={null}
import { z } from 'zod';
import { ethers } from 'ethers';

const AddressSchema = z.string().refine((addr) => {
  return ethers.isAddress(addr);
}, "Invalid Ethereum address");

const AmountSchema = z.string().refine((amount) => {
  try {
    ethers.parseEther(amount);
    return true;
  } catch {
    return false;
  }
}, "Invalid amount format");
```

### Rate Limiting

Implement rate limiting:

```typescript theme={null}
// src/middleware/rateLimit.ts
export class RateLimiter {
  private requests = new Map<string, number[]>();

  isAllowed(clientId: string, maxRequests: number, windowMs: number): boolean {
    const now = Date.now();
    const clientRequests = this.requests.get(clientId) || [];
    
    // Remove old requests outside the window
    const validRequests = clientRequests.filter(time => now - time < windowMs);
    
    if (validRequests.length >= maxRequests) {
      return false;
    }
    
    validRequests.push(now);
    this.requests.set(clientId, validRequests);
    
    return true;
  }
}
```

### Secure Storage

Implement secure storage for sensitive data:

```typescript theme={null}
// src/utils/encryption.ts
import crypto from 'crypto';

export class SecureStorage {
  private static readonly ALGORITHM = 'aes-256-cbc';

  static encrypt(text: string, password: string): string {
    const key = crypto.scryptSync(password, 'salt', 32);
    const iv = crypto.randomBytes(16);
    const cipher = crypto.createCipher(this.ALGORITHM, key);
    
    let encrypted = cipher.update(text, 'utf8', 'hex');
    encrypted += cipher.final('hex');
    
    return iv.toString('hex') + ':' + encrypted;
  }

  static decrypt(encryptedText: string, password: string): string {
    const [ivHex, encrypted] = encryptedText.split(':');
    const key = crypto.scryptSync(password, 'salt', 32);
    const iv = Buffer.from(ivHex, 'hex');
    const decipher = crypto.createDecipher(this.ALGORITHM, key);
    
    let decrypted = decipher.update(encrypted, 'hex', 'utf8');
    decrypted += decipher.final('utf8');
    
    return decrypted;
  }
}
```

## Contributing

### Code Style

Follow the established code style:

```typescript theme={null}
// Use TypeScript strict mode
// Prefer async/await over promises
// Use meaningful variable names
// Add JSDoc comments for public APIs

/**
 * Gets the balance of an address
 * @param address - The Ethereum address to check
 * @returns Promise resolving to balance in wei
 */
export async function getBalance(address: string): Promise<string> {
  // Implementation
}
```

### Pull Request Process

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Add tests for new functionality
5. Ensure all tests pass
6. Submit a pull request

### Documentation

Update documentation for new features:

* Add tool documentation to the appropriate files
* Update API references
* Include usage examples
* Update integration guides if needed

## Deployment

### Production Build

```bash theme={null}
# Clean previous build
npm run clean

# Build for production
npm run build

# Verify build
node dist/index.js --version
```

### Docker Deployment

Create a Dockerfile:

```dockerfile theme={null}
FROM node:18-alpine

WORKDIR /app

COPY package*.json ./
RUN npm ci --only=production

COPY dist/ ./dist/

EXPOSE 3000

CMD ["node", "dist/index.js"]
```

Build and run:

```bash theme={null}
docker build -t mcp-0g-server .
docker run -p 3000:3000 -e ZEROQ_RPC_URL=https://evmrpc-testnet.0g.ai mcp-0g-server
```

### Monitoring in Production

Set up monitoring and alerting:

```typescript theme={null}
// Health check endpoint
app.get('/health', (req, res) => {
  res.json({
    status: 'healthy',
    timestamp: new Date().toISOString(),
    uptime: process.uptime(),
    memory: process.memoryUsage()
  });
});
```

This development guide provides the foundation for extending and contributing to the MCP 0G Server. For specific questions or advanced use cases, refer to the community resources and documentation.