MCP Server Registry

MassGen includes a curated registry of recommended MCP (Model Context Protocol) servers that are automatically available when auto-discovery is enabled.

Overview

The MCP server registry provides pre-configured, tested MCP servers that extend agent capabilities. When you enable auto_discover_custom_tools: true in your configuration, these servers are automatically included if their API keys are available (or not required).

Registry Location: massgen/mcp_tools/server_registry.py

Available Servers

Context7

Purpose: Up-to-date code documentation for libraries and frameworks

Type: stdio (local) or streamable-http (remote)

API Key: Optional (CONTEXT7_API_KEY)

Connection:

mcp_servers:
  - name: "context7"
    type: "stdio"
    command: "npx"
    args: ["-y", "@upstash/context7-mcp"]

Tools:

• resolve_context7_library_id - Convert library names to Context7 IDs

• get_library_docs - Fetch version-specific documentation (1K-50K tokens)

Key Features:

• No API key required for basic use

• Get API key at https://context7.com/dashboard for higher rate limits

• Eliminates outdated information and hallucinated APIs

• Provides current, version-specific documentation

Important Notes:

• Outputs can be very large (5K-50K tokens)

• Recommended: Write output to file first, then parse

• Use topic parameter to narrow results

• Adjust tokens parameter (default: 5000, max: 50000)

Use Cases:

• Getting latest framework documentation (React, Next.js, Vue, etc.)

• Finding current API references

• Learning about new features in recent versions

• Avoiding outdated or hallucinated information

Example:

# See: massgen/configs/tools/mcp/context7_documentation_example.yaml

Brave Search

Purpose: Web search via Brave API

Type: stdio

API Key: Required (BRAVE_API_KEY)

Connection:

mcp_servers:
  - name: "brave_search"
    type: "stdio"
    command: "npx"
    args: ["-y", "@brave/brave-search-mcp-server"]
    env:
      BRAVE_API_KEY: "${BRAVE_API_KEY}"

Tools:

• brave_web_search - Perform web searches

• Additional tools for local search, summarization (Pro tier)

Key Features:

• Real-time web search results

• Free tier: 2000 queries/month

• Pro tier: Enhanced features (local search, summarization, extra snippets)

API Key Setup:

1. Sign up at https://brave.com/search/api/

2. Generate API key from dashboard

3. Add to .env: BRAVE_API_KEY="your_key_here"

Rate Limit Warning:

⚠️ Free tier limited to 2000 queries/month

• Execute searches sequentially, not in parallel

• Avoid repeated searches

• Combine multiple questions into single queries

• Consider Pro tier for heavy usage

Use Cases:

• Current events and recent information

• Latest trends and updates

• Real-time data queries

• Information not in LLM training data

• Fact verification

Example:

# See: massgen/configs/tools/mcp/brave_search_example.yaml

Exa Search

Purpose: AI-powered web search and page fetch via Exa’s official MCP server

Type: stdio

API Key: Required (EXA_API_KEY)

Connection:

mcp_servers:
  - name: "exa_search"
    type: "stdio"
    command: "npx"
    args: ["-y", "exa-mcp-server"]
    env:
      EXA_API_KEY: "${EXA_API_KEY}"

MassGen currently wires Exa through the official npm package (npx -y exa-mcp-server). Exa’s current docs also highlight a hosted MCP endpoint (https://mcp.exa.ai/mcp) for clients that support HTTP MCP directly.

Tools:

• web_search_exa - Search the web and return ready-to-use content

• web_fetch_exa - Read a webpage’s full content as clean markdown from a URL

• web_search_advanced_exa - Advanced search with category, domain, date, highlight, and summary controls

Key Features:

• Search the web with Exa’s AI-oriented ranking and content extraction

• Fetch a known page as clean markdown for summarization or downstream analysis

• Advanced search options documented by Exa include category, domain, and date filters

• Official Exa docs currently prefer the hosted MCP endpoint for HTTP-capable clients, while MassGen’s registry uses the official npm package form above

API Key Setup:

1. Sign up at https://exa.ai/

2. Generate API key from dashboard

3. Add to .env: EXA_API_KEY="your_key_here"

Use Cases:

• Research queries requiring semantic understanding

• Fetching and summarizing the full contents of a known page

• Category-specific searches (research papers, news, companies)

• Time-bounded or domain-restricted searches when advanced Exa tooling is enabled

Example:

# See: massgen/configs/tools/web-search/exa_search_example.yaml

Auto-Discovery

When auto_discover_custom_tools: true is set in your backend configuration, MassGen automatically includes registry servers that are available:

Always Included:

• Context7 (no API key required)

Conditionally Included:

• Brave Search (only if BRAVE_API_KEY is set in .env)

• Exa Search (only if EXA_API_KEY is set in .env)

Behavior:

1. Checks which registry servers have required API keys available

2. Merges available servers into mcp_servers configuration

3. Avoids duplicates if server is already manually configured

4. Logs which servers were added and which were skipped

Example:

agents:
  - id: "research_agent"
    backend:
      type: "gemini"
      model: "gemini-2.5-flash"
      auto_discover_custom_tools: true  # Automatically adds registry servers!

Log Output:

[gemini] Auto-discovery enabled: Added MCP servers from registry: context7
[gemini] Registry servers not added (missing API keys): brave_search (needs BRAVE_API_KEY)

Registry Summary Table

Server	Type	API Key	Rate Limits	Notes
Context7	stdio	Optional	None	Large outputs (write to files). Optional API key for higher rate limits.
Brave Search	stdio	Required	2000/month (free)	Avoid parallel queries. Pro tier available for heavy usage.
Exa Search	stdio	Required	Pay-per-use	AI-powered neural search. Supports category filtering, content extraction, and deep search.

Manual Configuration

You can manually configure any registry server without auto-discovery:

agents:
  - id: "my_agent"
    backend:
      type: "claude"
      model: "claude-sonnet-4"
      mcp_servers:
        - name: "context7"
          type: "stdio"
          command: "npx"
          args: ["-y", "@upstash/context7-mcp"]

This gives you full control over which servers to include and their configuration.

See Also

• MCP Integration - Complete MCP integration guide

• YAML Configuration Reference - YAML configuration schema

• massgen/configs/tools/mcp/ - Example configurations