#!/usr/bin/env node
/**
* MCP Client Sniffer
*
* A minimal MCP server that logs all initialize requests to capture:
* 1. clientInfo.name - What name the client sends
* 2. protocolVersion - What protocol version they use
* 3. capabilities - What capabilities they support
*
* Usage:
* 1. Configure this script as an MCP server in your client
* 2. Client connects and sends initialize request
* 3. This script logs the clientInfo and saves to client-info-log.json
* 4. Use the captured info to update client-registry.ts
*
* Example MCP config for Claude Desktop:
* {
* "mcpServers": {
* "client-sniffer": {
* "command": "node",
* "args": ["/path/to/ncp/scripts/mcp-client-sniffer.cjs"]
* }
* }
* }
*/
const fs = require('fs');
const path = require('path');
const LOG_FILE = path.join(process.cwd(), 'client-info-log.json');
const capturedClients = [];
// Load existing log if present
if (fs.existsSync(LOG_FILE)) {
try {
const existing = JSON.parse(fs.readFileSync(LOG_FILE, 'utf-8'));
capturedClients.push(...existing);
} catch (e) {
// Ignore
}
}
// Read from stdin (MCP protocol over stdio)
let buffer = '';
process.stdin.on('data', (chunk) => {
buffer += chunk.toString();
const lines = buffer.split('\n');
// Process complete lines
for (let i = 0; i < lines.length - 1; i++) {
const line = lines[i].trim();
if (!line) continue;
try {
const request = JSON.parse(line);
// Log all requests for debugging
fs.appendFileSync(
path.join(process.cwd(), 'mcp-sniffer-debug.log'),
`[${new Date().toISOString()}] ${line}\n`
);
if (request.method === 'initialize') {
const clientInfo = request.params?.clientInfo || { name: 'unknown', version: 'unknown' };
const timestamp = new Date().toISOString();
console.error('\n' + '='.repeat(70));
console.error('✨ CLIENT DETECTED!');
console.error('='.repeat(70));
console.error('Timestamp:', timestamp);
console.error('Client Name:', clientInfo.name);
console.error('Client Version:', clientInfo.version);
console.error('Protocol Version:', request.params?.protocolVersion || 'unknown');
console.error('='.repeat(70) + '\n');
// Save to log
capturedClients.push({
timestamp,
clientInfo,
protocolVersion: request.params?.protocolVersion,
capabilities: request.params?.capabilities
});
// Deduplicate by client name
const unique = {};
capturedClients.forEach(c => {
unique[c.clientInfo.name] = c;
});
fs.writeFileSync(LOG_FILE, JSON.stringify(Object.values(unique), null, 2));
console.error(`💾 Saved to ${LOG_FILE}\n`);
// Send initialize response
const response = {
jsonrpc: '2.0',
id: request.id,
result: {
protocolVersion: '2024-11-05',
serverInfo: {
name: 'mcp-client-sniffer',
version: '1.0.0'
},
capabilities: {
tools: {}
}
}
};
process.stdout.write(JSON.stringify(response) + '\n');
} else if (request.method === 'tools/list') {
// Respond to tools/list with empty list
const response = {
jsonrpc: '2.0',
id: request.id,
result: {
tools: []
}
};
process.stdout.write(JSON.stringify(response) + '\n');
} else if (request.method === 'notifications/initialized') {
// Ignore notifications (no response needed)
} else {
// Respond to unknown methods with error
const response = {
jsonrpc: '2.0',
id: request.id,
error: {
code: -32601,
message: 'Method not found'
}
};
process.stdout.write(JSON.stringify(response) + '\n');
}
} catch (e) {
console.error('Failed to parse JSON:', e.message);
}
}
// Keep the incomplete line
buffer = lines[lines.length - 1];
});
// Log startup
console.error('🎯 MCP Client Sniffer Started');
console.error('Waiting for client connections...\n');
console.error('Configure this script as an MCP server in your client:');
console.error(` "command": "node"`);
console.error(` "args": ["${__filename}"]\n`);
