mcp_arena

mcp_arena is an opinionated Python library for building MCP (Model Context Protocol) servers: 30+ ready-to-use presets you can stand up in one call, plus a thin bridge into a LangChain agent.

The headline feature is the MCP server — drop one in, run it, talk to it over stdio / SSE / HTTP:

# server.py
from mcp_arena.presents.github import GithubMCPServer

server = GithubMCPServer(
    token="ghp_…",                        # or pull from $GITHUB_TOKEN
    host="127.0.0.1",
    port=8000,
    transport="stdio",                     # stdio (default) | sse | http
    debug=False,
)

if __name__ == "__main__":
    server.run()

Any MCP client can now talk to it. The full preset list, constructor kwargs, and BaseMCPServer surface are in MCP_SERVERS_GUIDE.md. The LangChain-agent bridge is at the bottom of this README — read after you’ve understood the server side.

0.4.0 release: the old ReflectionAgent / ReactAgent / PlanningAgent / policies / memory / router stack is gone. The agent subsystem is now one function: make_mcp_agent. Migration guide in CHANGELOG.md.

Why mcp_arena?

• 30+ ready-to-run MCP server presets. Slack, GitHub, Notion, Gmail, PostgreSQL, Mongo, Redis, S3, browsers, video, audio, PDFs, QR codes, webscraping, and more — install one extra, import one class, call server.run(). Any MCP-compatible client can talk to it.
• Each preset is a real BaseMCPServer. Tools register at construction, are exposed on _registered_tools for inspection, and the server can be started over stdio / SSE / HTTP in one call.
• Lazy-loaded presets. mcp_arena.presents.__init__ AST-scans the directory; importing one preset doesn’t pull in unrelated deps.
• Drop-in extension. New MCP server? Write a *Server subclass in mcp_arena/presents/.py; it’s auto-discovered.
• Optional LangChain bridge. make_mcp_agent(llm, servers, ...) is the only function that wires the same server objects into a LangGraph agent. Forward any create_agent kwarg through **kwargs.

Install

⚠️ pip install mcp-arena ships three general-purpose presets in core — LocalOperationsMCPServer, GenericAPIMCPServer, and SMTPServer — so you can run a real MCP server with zero extra setup. Every other preset is gated behind an extra so you only pay for the third-party packages you actually need.

pip install mcp-arena                       # 3 core presets work out of the box
pip install "mcp-arena[github]"             # + GitHub preset (PyGithub)
pip install "mcp-arena[github,slack]"       # + several presets