MCP Servers with Claude: Custom Toolkits for Domain-Specific Agents

# MCP Servers with Claude: Custom Toolkits for Domain-Specific Agents ## Introduction Claude's tool-using capabilities allow it to interact with external APIs, databases, and services, making it ideal for building sophisticated AI agents. But generic tools fall short for specialized domains like healthcare or finance, where compliance, precision, and domain knowledge are paramount. Enter **MCP (Model Context Protocol) servers**—lightweight, extensible servers that provide Claude with tailored toolkits via a standardized protocol. MCP servers act as intermediaries, exposing domain-specific functions as callable tools. Claude can then invoke these tools dynamically during conversations, fetching real-time data or performing computations securely. This guide dives deep into setting up MCP servers, with practical examples for finance (stock analysis) and healthcare (patient record simulation). Whether you're a developer building enterprise agents or a business user automating workflows, MCP unlocks Claude's full potential for your niche. ## What are MCP Servers? MCP is Anthropic's protocol for structured tool interactions, building on Claude's native tool-use schema. An MCP server: - Hosts custom functions (tools) with JSON schemas for Claude to discover and call. - Handles authentication, rate limiting, and error recovery. - Integrates seamlessly with Claude API, Claude Code CLI, or agents like those in n8n/Zapier. Key benefits: - **Domain isolation**: Tools only access permitted data/APIs. - **Scalability**: Deploy on Vercel, AWS Lambda, or local for dev. - **Claude-native**: No custom parsing—Claude handles MCP XML/JSON natively. Compared to raw API calls, MCP servers provide: | Feature | Direct API | MCP Server | |---------|------------|------------| | Schema Discovery | Manual | Automatic | | Security | Exposed | Proxied | | Caching/Logic | None | Built-in | ## Prerequisites - Node.js 18+ or Python 3.10+ (we'll use Node for examples). - Claude API key (from console.anthropic.com). - Familiarity with Claude's tool use (e.g., `tools` parameter in API). - Optional: Docker for deployment, ngrok for local testing. Install dependencies: ```bash npm init -y npm install express axios cors helmet # Or Python: pip install fastapi uvicorn pydantic ``` ## Setting Up a Basic MCP Server We'll build a Node.js MCP server using Express. The server exposes a `/tools` endpoint for schema discovery and `/call` for execution. ### Step 1: Server Skeleton Create `mcp-server.js`: ```javascript import express from 'express'; import cors from 'cors'; import helmet from 'helmet'; const app = express(); app.use(helmet()); app.use(cors()); app.use(express.json()); const PORT = process.env.PORT || 3000; // Tool registry const tools = new Map(); // Schema endpoint app.get('/tools', (req, res) => { res.json(Array.from(tools.values())); }); // Call endpoint app.post('/call', async (req, res) => { const { tool_name, parameters } = req.body; const tool = tools.get(tool_name); if (!tool) return res.status(404).json({ error: 'Tool not found' }); try { const result = await tool.handler(parameters); res.json({ result }); } catch (error) { res.status(500).json({ error: error.message }); } }); app.listen(PORT, () => console.log(`MCP Server running on port ${PORT}`)); ``` Run with `node mcp-server.js`. ### Step 2: Register a Tool Add a simple calculator tool: ```javascript const calculatorTool = { name: 'calculator', description: 'Perform basic arithmetic', inputSchema: { type: 'object', properties: { expression: { type: 'string', description: 'Math expression e.g., 2+2' } }, required: ['expression'] }, handler: async ({ expression }) => { // Use safe eval or math.js in prod const result = Function('return ' + expression)(); return { value: result }; } }; tools.set('calculator', calculatorTool); ``` Test: `curl http://localhost:3000/tools` lists schemas; `curl -X POST /call -d '{"tool_name":"calculator","parameters":{"expression":"5*3"}}'` returns `{ "result": { "value": 15 } }`. ## Building Domain-Specific Toolkits ### Finance Toolkit: Stock Analysis For finance agents, create tools for quotes, historical data, and risk metrics. Use Alpha Vantage API (free tier). ```javascript const getStockQuote = { name: 'get_stock_quote', description: 'Fetch real-time stock quote', inputSchema: { type: 'object', properties: { symbol: { type: 'string', example: 'AAPL' } }, required: ['symbol'] }, handler: async ({ symbol }) => { const apiKey = process.env.ALPHA_VANTAGE_KEY; const response = await fetch(`https://www.alphavantage.co/query?function=GLOBAL_QUOTE&symbol=${symbol}&apikey=${apiKey}`); const data = await response.json(); const quote = data['Global Quote']; return { price: quote['05. price'], change: quote['09. change'], volume: quote['06. volume'] }; } }; tools.set('get_stock_quote', getStockQuote); // Add more: get_historical, calculate_risk, etc. ``` **Pro Tip**: Cache results with Redis for high-volume agents. ### Healthcare Toolkit: Patient Insights (Simulation) For HIPAA-compliant sims (use mock data in prod previews): ```javascript const getPatientVitals = { name: 'get_patient_vitals', description: 'Retrieve anonymized patient vitals', inputSchema: { type: 'object', properties: { patient_id: { type: 'string' } }, required: ['patient_id'] }, handler: async ({ patient_id }) => { // Mock DB lookup const mockData = { 'P001': { heart_rate: 72, blood_pressure: '120/80', temp: 98.6 }, // ... }; return mockData[patient_id] || { error: 'Patient not found' }; } }; tools.set('get_patient_vitals', getPatientVitals); ``` **Security Note**: In production, use JWT auth on `/call`, audit logs, and encrypt sensitive fields. ## Integrating MCP with Claude Point Claude to your server via the `tools` array in API calls. ### Using Claude API ```javascript import Anthropic from '@anthropic-ai/sdk'; const client = new Anthropic({ apiKey: process.env.ANTHROPIC_API_KEY }); const MCP_URL = 'http://localhost:3000'; // or deployed URL const tools = [ { name: 'get_stock_quote', description: 'Fetch real-time stock quote', input_schema: { /* fetch from /tools */ } // Dynamically fetch } ]; const msg = await client.messages.create({ model: 'claude-3-5-sonnet-20240620', max_tokens: 1024, tools, messages: [{ role: 'user', content: 'What\'s the current price of AAPL?' }], tool_choice: 'auto' }); // Handle tool_use blocks in response if (msg.content[0].type === 'tool_use') { const toolCall = msg.content[0]; const result = await fetch(`${MCP_URL}/call`, { method: 'POST', headers: { 'Content-Type': 'application/json' }, body: JSON.stringify({ tool_name: toolCall.name, parameters: toolCall.input }) }).then(r => r.json()); // Send back to Claude } ``` ### With Claude Code CLI In `claude-code` projects, configure `mcp_servers: [{ url: 'http://localhost:3000' }]` in `.claude.toml` for seamless integration. ## Building a Domain Agent Combine tools into an agent loop: 1. User query → Claude plans tools. 2. Execute via MCP → Return results. 3. Claude synthesizes response. Example agent prompt: ```xml <system> You are a Finance Analyst. Use tools for data, reason step-by-step. </system> ``` Test workflow: - Query: "Analyze AAPL's performance." - Claude calls `get_stock_quote` → MCP fetches → Claude: "AAPL at $230, up 2%..." ## Deployment and Best Practices - **Deploy**: Vercel (`vercel --prod`), Heroku, or AWS. ```json // vercel.json { "functions": { "mcp-server.js": { "runtime": "nodejs18.x" } } } ``` - **Auth**: API keys in headers; Claude proxies requests. - **Error Handling**: Always return structured JSON. - **Monitoring**: Integrate Sentry/Prometheus. - **Scalability**: Serverless for bursts; WebSockets for streaming. - **SEO/Compliance**: Finance? SEC rules. Healthcare? Mock till certified. Advanced: Multi-MCP chaining—Claude calls one tool that triggers another server. ## Real-World Use Cases - **HR**: Resume parsing, compliance checks. - **Marketing**: Sentiment analysis via custom NLP tools. - **Engineering**: Code review APIs integrated with GitHub. ## Conclusion MCP servers transform Claude into a domain powerhouse. Start with the basic setup above, customize for your industry, and deploy. Experiment with Claude Opus for complex reasoning. Resources: - [Anthropic Tool Use Docs](https://docs.anthropic.com) - [Claude Directory MCP Hub](https://claudedirectory.com/mcp) Fork the repo: [github.com/claude-directory/mcp-examples](https://github.com/claude-directory/mcp-examples) (hypothetical). *Word count: ~1450*