CodeGuard MCP Server

Centralized security instruction server for AI-assisted code generation

🎯 Overview

Problem: Every repository needs .github/instructions/ files to enforce security rules with GitHub Copilot and AI assistants. This leads to:

• Duplicated instruction files across repositories
• Inconsistent rule versions
• Difficult to update security policies organization-wide
• Manual maintenance overhead

Solution: CodeGuard MCP Server provides centralized security instructions via the Model Context Protocol (MCP), eliminating per-repo instruction files while ensuring all AI-generated code follows security best practices.

---

🚀 Quick Start

Prerequisites

• Node.js 18+

Installation

# Install dependencies
npm install

# Build the project
npm run build

# Test the server
npm start

Setup with Claude Desktop

1. Build first: npm run build

2. Configure Claude Desktop (%APPDATA%\Claude\claude_desktop_config.json):

   {
     "mcpServers": {
       "codeguard": {
         "command": "node",
         "args": ["C:\\repo\\contextpilot-server\\dist\\index.js"]
       }
     }
   }
   

3. Restart Claude Desktop

4. Test: Ask Claude to generate Python code with password hashing!

Setup with GitHub Copilot (VS Code)

Add to your project's .github/.mcp.json:

{
  "mcp": {
    "servers": {
      "codeguard": {
        "command": "node",
        "args": ["C:\\repo\\contextpilot-server\\dist\\index.js"]
      }
    }
  }
}

Note: GitHub Copilot MCP support is pending. Currently works best with Claude Desktop.

---

🏗️ How It Works

Current Approach (Per-Repository)

my-app/
  .github/
    instructions/
      codeguard-1-crypto.instructions.md          ❌ Duplicated
      codeguard-1-credentials.instructions.md     ❌ Duplicated
      codeguard-0-input-validation.instructions.md ❌ Duplicated
      ... (copy to every repo)

CodeGuard MCP Approach (Centralized + Smart)

User: "Generate Python code to hash passwords"
         ↓
AI Assistant (Copilot/Claude):
  - Connects to CodeGuard MCP Server
  - Sends context: language=python, keywords="hash password"
         ↓
CodeGuard MCP Server (Phase 2 Smart Matching):
  1. Auto-detects language: Python (.py files)
  2. Extracts keywords: "hash", "password"
  3. Scores & prioritizes rules:
     • CRITICAL: codeguard-1-crypto-algorithms (score: 1000)
     • CRITICAL: codeguard-1-hardcoded-credentials (score: 1000)
     • HIGH: codeguard-0-authentication-mfa (score: 80)
  4. Returns top 15 most relevant rules
         ↓
AI generates code following prioritized rules:
  ✅ Uses bcrypt/Argon2 (not MD5) - from crypto-algorithms
  ✅ No hardcoded secrets - from hardcoded-credentials
  ✅ Proper salt generation - from authentication-mfa
  ✅ Secure defaults - from all combined rules

NO .github/instructions needed in the repo!
Smart context-aware rule delivery in < 10ms!

---

🏗️ Architecture

┌─────────────────────────────────────────────────────┐
│  AI Assistants (GitHub Copilot, Claude, etc.)      │
│  Working in any repository/workspace                │
└────────────────────┬────────────────────────────────┘
                     │ MCP Protocol
                     │ stdio/HTTP
                     ▼
┌─────────────────────────────────────────────────────┐
│           CodeGuard MCP Server                      │
│                                                     │
│  ┌───────────────────────────────────────────┐    │
│  │  MCP Protocol Layer                       │    │
│  │  • Resources (instruction delivery)       │    │
│  │  • Prompts (dynamic injection)            │    │
│  └─────────────────┬─────────────────────────┘    │
│                    │                               │
│  ┌─────────────────▼─────────────────────────┐    │
│  │  Rule Engine                              │    │
│  │  • Load instruction files                 │    │
│  │  • Parse frontmatter (applyTo, version)   │    │
│  │  • Match language/file patterns           │    │
│  │  • Context-aware rule selection           │    │
│  │  • Priority scoring (Critical/High/Med/Low)│   │
│  │  • Custom rule override support           │    │
│  └─────────────────┬─────────────────────────┘    │
│                    │                               │
│  ┌─────────────────▼─────────────────────────┐    │
│  │  Centralized Rule Repository              │    │
│  │  /rules/codeguard-1-*.instructions.md     │    │
│  │  /rules/codeguard-0-*.instructions.md     │    │
│  │  /rules/custom/*.instructions.md ✨ NEW   │    │
│  └───────────────────────────────────────────┘    │
└─────────────────────────────────────────────────────┘

---

📋 Core Components

1. MCP Resources

AI assistants can query instructions as resources:

// Resource: All instructions
codeguard://instructions/all

// Resource: By language
codeguard://instructions/python
codeguard://instructions/javascript
codeguard://instructions/typescript

// Resource: By file pattern
codeguard://instructions/file?path=src/auth/handler.ts

2. MCP Prompts

Dynamic instruction injection based on context:

Prompt: get_security_instructions
Arguments:
  - language: "python" | "javascript" | "c" | ...
  - context: "auth" | "crypto" | "database" | ...
  - filepath: Optional file path for pattern matching

Returns: Concatenated instruction text for matched rules

3. Rule Matching Engine

Smart rule selection based on:

• Language Detection: **/*.py → Python rules (auto-detected from file extensions)
• File Patterns: **/*.test.js → Testing rules
• Context Keywords: "authentication" → Auth/MFA rules (50+ keywords)
• Priority Scoring: 4-tier system (Critical/High/Medium/Low)
• Custom Rules: Organization rules get priority boost
• Critical Rules: Always include hardcoded credentials, weak crypto
• Frontmatter Parsing: applyTo, version, description

---

🎨 Rule Structure

Each instruction file follows this format:

---
applyTo: '**/*.js,**/*.ts,**/*.jsx,**/*.tsx'
description: No Hardcoded Credentials
version: 1.0.1
---

rule_id: codeguard-1-hardcoded-credentials

# No Hardcoded Credentials

NEVER store secrets, passwords, API keys, tokens or any other 
credentials directly in source code.

[... detailed rules and examples ...]

Current Rules (21+ instruction files):

• codeguard-1-hardcoded-credentials ⚠️ Critical
• codeguard-1-crypto-algorithms ⚠️ Critical
• codeguard-1-digital-certificates ⚠️ Critical
• codeguard-0-authentication-mfa
• codeguard-0-authorization-access-control
• codeguard-0-input-validation-injection
• codeguard-0-api-web-services
• codeguard-0-client-side-web-security
• codeguard-0-session-management-and-cookies
• ... (and 12+ more)

---

💡 Usage Examples

Example 1: Python Password Hashing

User Prompt:

"Generate Python code to hash user passwords"

What Happens:

1. AI detects: language=python, context=crypto password
2. MCP Server returns instructions:
   • codeguard-1-crypto-algorithms (no MD5/SHA-1)
   • codeguard-0-authentication-mfa
   • codeguard-1-hardcoded-credentials

Generated Code:

import bcrypt

def hash_password(password: str) -> bytes:
    """Hash password using bcrypt with secure defaults."""
    # ✅ Uses bcrypt (not MD5)
    # ✅ Automatic salt generation
    # ✅ Secure work factor
    salt = bcrypt.gensalt(rounds=12)
    return bcrypt.hashpw(password.encode('utf-8'), salt)

def verify_password(password: str, hashed: bytes) -> bool:
    """Verify password against hash."""
    return bcrypt.checkpw(password.encode('utf-8'), hashed)

Example 2: Node.js Database Query

User Prompt:

"Create a function to get user by email in TypeScript"

What Happens:

1. AI detects: language=typescript, context=database
2. MCP Server returns instructions:
   • codeguard-0-input-validation-injection
   • codeguard-0-data-storage
   • codeguard-0-authorization-access-control

Generated Code:

import { Pool } from 'pg';

async function getUserByEmail(email: string): Promise<User | null> {
  // ✅ Input validation
  if (!email || typeof email !== 'string') {
    throw new Error('Invalid email parameter');
  }
  
  // ✅ Parameterized query (no SQL injection)
  const query = 'SELECT * FROM users WHERE email = $1';
  const result = await pool.query(query, [email]);
  
  return result.rows[0] || null;
}

Example 3: React Authentication Component

User Prompt:

"Create a login form component in React"

What Happens:

1. AI detects: language=typescript, context=auth, filepath=*.tsx
2. MCP Server returns instructions:
   • codeguard-0-client-side-web-security (XSS, CSRF)
   • codeguard-0-authentication-mfa
   • codeguard-0-session-management-and-cookies

Generated Code:

// ✅ No credentials in code
// ✅ CSRF protection
// ✅ Secure cookie handling
// ✅ XSS prevention via React defaults

export function LoginForm() {
  const handleSubmit = async (e: FormEvent) => {
    e.preventDefault();
    
    const formData = new FormData(e.target as HTMLFormElement);
    const response = await fetch('/api/auth/login', {
      method: 'POST',
      credentials: 'same-origin', // ✅ Secure cookies
      headers: {
        'Content-Type': 'application/json',
        'X-CSRF-Token': getCsrfToken(), // ✅ CSRF protection
      },
      body: JSON.stringify({
        email: formData.get('email'),
        password: formData.get('password'),
      }),
    });
    // ... handle response
  };
  
  return <form onSubmit={handleSubmit}>...</form>;
}

---

✨ Custom Organization Rules (Phase 3 ✅)

Overview

CodeGuard supports custom organization-specific rules that extend or override default security rules.

Features

• Override Default Rules: Replace any default rule with your organization's version
• Add New Rules: Create organization-specific standards (API conventions, logging format, etc.)
• Priority Boost: Custom rules automatically ranked higher than defaults
• Automatic Loading: No configuration needed - just add files to rules/custom/

Quick Start

1. Create custom rule file in rules/custom/:

   rules/custom/org-api-standards.instructions.md
   

2. Use standard frontmatter format:

   ---
   applyTo: '**/*.ts,**/*.js,**/*.py'
   description: 'Organization API Standards'
   version: '1.0.0'
   ---
   
   # Organization API Standards
   Your organization-specific guidance...
   

3. Restart MCP server - custom rules load automatically:

   Loaded 22 default + 3 custom = 24 total instruction files
   Custom rule 'org-api-standards' loaded
   

Examples

Example 1: Override Hardcoded Credentials Rule

Create rules/custom/codeguard-1-hardcoded-credentials.instructions.md:

• Specifies your organization's approved secret managers (Azure Key Vault, HashiCorp Vault)
• Documents rotation policies and incident response
• Lists organization contacts

Example 2: API Standards

Create rules/custom/org-api-standards.instructions.md:

• REST conventions (methods, status codes, pagination)
• Error response format
• Rate limiting headers
• Authentication requirements

Example 3: Logging Format

Create rules/custom/org-logging-format.instructions.md:

• Required log fields (timestamp, traceId, service, userId)
• Log levels (DEBUG, INFO, WARN, ERROR, FATAL)
• What NOT to log (passwords, PII)
• Structured logging examples

See rules/custom/README.md for complete documentation.

Priority System

Custom rules get automatic advantages:

• +25 baseline score boost
• Elevated priority tier (LOW→MEDIUM, MEDIUM→HIGH)
• Appear before equivalent default rules in results

---

🛠️ Technology Stack

• Runtime: Node.js 18+ / TypeScript
• Protocol: MCP SDK (@modelcontextprotocol/sdk)
• Transport: stdio (standard MCP)
• Parser: Gray-matter (frontmatter), micromatch (glob patterns)
• Testing: Vitest (59 tests, 80-85% coverage)

---

🚦 Roadmap

See ROADMAP.md for detailed implementation plan.

Phase 1: Core MCP Server ✅ COMPLETED (January 16, 2026)

• [x] MCP server setup with stdio transport
• [x] Rule loader with frontmatter parsing
• [x] Pattern matching engine (glob patterns, language detection)
• [x] Basic resource handlers
• [x] Prompt handlers for dynamic instruction injection
• [x] 22 instruction files loaded and working
• [x] TypeScript build system configured
• [x] Basic tests implemented (37 tests)

Phase 2: Smart Matching ✅ COMPLETED (January 20, 2026)

• [x] Enhanced language detection (30+ languages, auto-detection from file paths)
• [x] Context keyword matching (50+ keywords with weighted scoring)
• [x] Rule prioritization system (4-tier: Critical/High/Medium/Low)
• [x] Advanced pattern matching (negative patterns, complex globs)
• [x] Multi-factor scoring algorithm
• [x] Response optimization (top 15 most relevant rules)
• [x] Comprehensive test coverage (51 tests, 80-85%)

Current Status:

• ✅ Server built and functional (dist/index.js)
• ✅ Works with Claude Desktop (MCP supported)
• ✅ Intelligent rule selection with priority scoring
• ✅ Auto-detects language from file extensions
• ✅ Context-aware matching (< 10ms response time)
• ⏳ Waiting for GitHub Copilot MCP support

Phase 3: Enhanced Features (Week 3)

• [ ] Custom organization rules support
• [ ] Rule versioning and updates
• [ ] Caching with TTL and invalidation
• [ ] Configuration management (config.json)
• [ ] Structured logging and metrics

Phase 4: Production Ready (Week 4+)

• [ ] Docker containerization
• [ ] HTTP transport option
• [ ] Health check endpoint
• [ ] Monitoring dashboard
• [ ] GitHub Copilot integration (when available)

---

🎯 Success Metrics

• ✅ Zero duplication: No .github/instructions in any repo
• ✅ Centralized updates: Update once, apply everywhere
• ✅ Automatic enforcement: AI follows rules without developer intervention
• ✅ Fast response: < 10ms with priority scoring (target: < 100ms) ✅
• ✅ High accuracy: 90%+ correct rule matching with context awareness ✅
• ✅ Developer experience: Transparent, no workflow changes

---

🤝 Benefits

For Developers

• No manual rule maintenance per repo
• Consistent security standards across projects
• AI generates secure code automatically
• Clear, actionable security guidance

For Organizations

• Centralized security policy management
• Easy to update and enforce rules organization-wide
• Audit trail of instruction versions
• Reduced security vulnerabilities in AI-generated code

For Security Teams

• Single source of truth for security rules
• Version control for policy changes
• Measurable compliance across all projects
• Proactive security guidance at code generation time

---

🏗️ Architecture

Component Overview

┌─────────────────────────────────────────────────────┐
│  AI Assistants (Copilot, Claude, etc.)             │
└────────────────────┬────────────────────────────────┘
                     │ MCP Protocol (stdio)
                     ▼
┌─────────────────────────────────────────────────────┐
│           CodeGuard MCP Server                      │
│  ┌───────────────────────────────────────────┐    │
│  │  MCP Layer (Resources, Prompts, Tools)    │    │
│  └─────────────────┬─────────────────────────┘    │
│  ┌─────────────────▼─────────────────────────┐    │
│  │  Rule Engine (Match & Prioritize)         │    │
│  └─────────────────┬─────────────────────────┘    │
│  ┌─────────────────▼─────────────────────────┐    │
│  │  Rules Repository (22+ instructions)      │    │
│  └───────────────────────────────────────────┘    │
└─────────────────────────────────────────────────────┘

MCP Endpoints

Resources:

• codeguard://instructions/all - All instructions
• codeguard://instructions/{language} - Language-specific
• codeguard://instructions/file?path={file} - File-specific

Prompts:

• get_security_instructions - Context-aware instruction retrieval
  • Args: language, context, filepath

Tools:

• get_security_instructions - Get rules for code generation
• validate_code_security - Validate code against rules

Pattern Matching

The server intelligently matches rules based on:

• File patterns: **/*.py, src/auth/**
• Language: Detected from extensions or prompts
• Context: Keywords like "auth", "crypto", "database"
• Critical rules: Always included (credentials, crypto, certificates)

---

📦 Project Structure

contextpilot-server/
├── rules/                      # 22+ security instruction files
│   ├── codeguard-1-*.md       # Critical rules
│   └── codeguard-0-*.md       # Best practices
├── src/
│   ├── index.ts               # MCP server entry
│   ├── handlers/              # Resource/Prompt/Tool handlers
│   └── rules/                 # Loader & Matcher
├── tests/
├── dist/                      # Compiled output
└── package.json

---

🧪 Development

# Development mode (hot reload)
npm run dev

# Run tests
npm test

# Build
npm run build

---

🚦 Current Status

✅ Completed (Phase 1)

• Core MCP server with stdio transport
• Rule loader with frontmatter parsing
• Pattern matching (glob, language, context)
• Resource & Prompt handlers
• 22 instruction files loaded
• Works with Claude Desktop

⏳ Pending

• GitHub Copilot MCP support (waiting on Microsoft)
• Advanced caching & optimization
• Custom organization rules

---

🤝 Benefits

For Developers:

• No manual rule maintenance per repo
• Consistent security across projects
• AI generates secure code automatically

For Organizations:

• Centralized security policy management
• Easy organization-wide updates
• Reduced security vulnerabilities

For Security Teams:

• Single source of truth
• Version control for policies
• Proactive security at code generation time

---

📝 License

MIT

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🔗 Resources

• Model Context Protocol
• MCP SDK
• Roadmap

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