Factcheck

An MCP Server for validating code or content against the official Model Context Protocol (MCP) specification to ensure technical accuracy and prevent the spread of misinformation.

📦 View in MCP Registry - Available in the official MCP Registry

📋 View Project Roadmap - See planned features and development progress

🏗️ Design Documentation - Technical design and implementation details

Overview

The MCP Fact-Check MCP Server helps ensure technical accuracy when coding or writing about MCP by comparing content against official specifications. It uses:

• Semantic search with OpenAI embeddings to find relevant specification sections
• AI-powered validation to detect inaccuracies and suggest corrections
• Compound claim decomposition to validate complex statements with multiple assertions
• Multiple spec versions support (draft, 2025-06-18, 2025-03-26, 2024-11-05)

Features

MCP Tools Exposed

1. check_mcp_claim - Comprehensive validation of MCP-related content

   • Validates multi-claim content (documentation, tutorials, bullet points)
   • Automatically decomposes compound claims (e.g., "X and Y") for accurate validation
   • Provides step-by-step validation workflow
   • Identifies missing best practices and modal verb issues
   • Returns corrected content with confidence scores

2. check_mcp_quick_fact - Quick fact-checking for single MCP claims

   • Validates single sentences or quick questions
   • Returns concise ✓/✗ verdict with explanation
   • Uses aggressive search strategies for accuracy
   • Perfect for "Does MCP support X?" questions

3. search_spec - Searches MCP specifications using semantic similarity

   • Returns most relevant specification sections
   • Supports all specification versions

4. list_spec_versions - Lists available MCP specification versions

   • Shows version dates and descriptions
   • Indicates which version is current

MCP Prompts Available

1. migrate-mcp-content - Guides content migration between MCP specification versions

   • Validates content against source specification first
   • Identifies changes between specification versions
   • Provides step-by-step migration guidance
   • Works with any type of MCP-related content
   • Preserves the original tone, style, and voice when making corrections or suggestions

   Parameters:

   • current_version (required): Source MCP specification version (e.g., "2024-11-05", "2025-06-18")
   • target_version (required): Target MCP specification version to migrate to (e.g., "draft")
   • update_scope (optional): Determines how aggressive the migration should be
     • critical_only: Fix only critical inaccuracies and breaking changes (minimal changes)
     • enhancement_focused: Fix issues and improve clarity, align with best practices
     • comprehensive: Complete review with all improvements and enhanced clarity
     • Default: comprehensive

Installation

The MCP Fact-Check server is available through the Model Context Protocol registry. Install it directly from your MCP client:

For Claude Desktop and other MCP clients:

• Search for "mcp-factcheck" in your client's server marketplace
• Click install
• Provide your OpenAI API key when prompted

That's it! The server will be automatically configured and ready to use.

For developers: If you need to build from source or contribute to the project, see INSTALL.md for development setup instructions.

Observability

Visual Tracing with Arize Phoenix

For a beautiful, AI-focused trace visualization UI, set up Arize Phoenix:

1. Install and start Phoenix:

# Install Phoenix
pipx install arize-phoenix

# Start Phoenix server
phoenix serve

2. Update the Host config to send traces to Phoenix:

{
  "mcpServers": {
    "mcp-factcheck": {
      "command": "/path/to/bin/mcp-factcheck-server",
      "args": [
        "--data-dir",
        "/path/to/data/embeddings",
        "--telemetry",
        "--otlp-endpoint",
        "http://localhost:6006"
      ],
      "env": {
        "OPENAI_API_KEY": "your-api-key"
      }
    }
  }
}

3. View traces at: http://localhost:6006

What you'll see in Phoenix:

• Beautiful AI-focused interface designed for LLM applications
• Complete validation pipeline timeline with clear visual hierarchy
• Embedding generation performance and OpenAI API call tracking
• Vector search visualization with similarity scores
• Per-chunk validation confidence levels and quality metrics
• Cost tracking for OpenAI API usage (or whichever llm is being used for embedding the input content/code)
• Clean, intuitive navigation focused on AI workflows

Phoenix is specifically designed for AI/ML observability and provides a much more user-friendly experience than traditional tracing tools.

Development

Building

# Build all components
go build -o bin/mfc ./cmd/server
go build -o bin/specloader ./utils/cmd

# Run tests
go test ./...

Updating Specifications

The project includes pre-extracted MCP specifications and embeddings for all versions. To check when the draft specification was last updated, see data/SPEC_METADATA.json:

# View draft update information
cat data/SPEC_METADATA.json | jq '.specs.draft'

To update the draft specification:

./bin/specloader spec --version draft
./bin/specloader embed --version draft
./bin/specloader embed --version draft-fine

To add a new specification version:

./bin/specloader spec --version 2025-12-15
./bin/specloader embed --version 2025-12-15
./bin/specloader embed --version 2025-12-15-fine

All specification extraction dates and source commits are automatically tracked in data/SPEC_METADATA.json.

Testing Tools

Test the server using the included test client:

# Build test client
go build -o bin/factcheck-curl ./cmd/factcheck-curl

# Test tools
./bin/factcheck-curl --cmd ./bin/mfc --data-dir ./data/embeddings tools/list
./bin/factcheck-curl --cmd ./bin/mfc --data-dir ./data/embeddings tools/call validate_content '{"content":"MCP is a protocol"}'

# Test prompts
./bin/factcheck-curl --cmd ./bin/mfc --data-dir ./data/embeddings prompts/list

# Get migration prompt with minimal parameters
./bin/factcheck-curl --cmd ./bin/mfc --data-dir ./data/embeddings prompts/get migrate-mcp-content '{"current_version":"2024-11-05","target_version":"draft"}'

# Get migration prompt with all parameters
./bin/factcheck-curl --cmd ./bin/mfc --data-dir ./data/embeddings prompts/get migrate-mcp-content '{
  "current_version": "2024-11-05",
  "target_version": "2025-06-18",
  "update_scope": "critical_only"
}'

Architecture

See DESIGN.md for the complete architecture documentation.

Environment Variables

• OPENAI_API_KEY - Required for embedding generation and content validation
• GITHUB_TOKEN - Optional, for higher GitHub API rate limits when extracting specs

License

MIT License. See LICENSE for details.