MCPLite

valve

Python implementation of the Model Context Protocol (MCP) for building servers that expose tools, resources, and prompts to LLM applications.

Project Purpose

Valve provides a framework for creating MCP-compliant servers and integrating them into LLM applications. It handles protocol negotiation, message routing, transport layer abstractions (stdio, direct, SSE), and provides a host orchestration layer that manages multiple MCP servers simultaneously. The framework enables LLMs to interact with external data sources and tools through a standardized protocol.

Architecture Overview

• MCPLite: Server-side framework for defining MCP servers using decorators. Provides @tool, @resource, and @prompt decorators for registering capabilities.
• Host: Orchestration engine that manages multiple MCP clients, aggregates capabilities, generates system prompts, and implements agent loops for LLM interactions.
• Client: MCP client implementation that connects to servers, performs capability negotiation, and sends requests.
• Server: Message processor that routes incoming MCP requests to registered primitives and returns responses.
• Transport Layer: Abstractions for communication including DirectTransport (in-process), StdioTransport (subprocess via stdio), and SSETransport (HTTP SSE).
• Primitives: Core MCP abstractions including MCPTool, MCPResource, MCPResourceTemplate, and MCPPrompt that wrap Python functions with MCP metadata.
• Messages: Pydantic models for MCP protocol messages including requests, responses, notifications, and errors conforming to JSON-RPC 2.0.
• Registry: ServerRegistry holds server-side primitives with executable code; ClientRegistry holds client-side definitions for capability discovery.
• Inventory: Server discovery and management system that scans directories for available MCP servers and maintains metadata.
• MCPChat: Chat interface built on Chain framework that adds MCP capabilities to conversational LLM applications.

Dependencies

Major Dependencies:

• pydantic: Data validation and serialization
• requests: HTTP client for fetch server
• beautifulsoup4: HTML parsing
• markdownify: HTML to Markdown conversion
• fastapi: Web framework for SSE transport
• sse-starlette: SSE support for FastAPI
• aiohttp: Async HTTP client
• rich: Terminal formatting and output

Local Dependencies:

• Chain: LLM framework providing Model, Message, MessageStore, Prompt, and Chat classes (appears to be an internal dependency)

API Documentation

MCPLite

class MCPLite:
    def __init__(self, transport: Optional[Transport | str] = None)

Main class for creating MCP servers.

Key Methods:

def tool(self, func: Callable) -> Callable

Decorator to register a function as an MCP tool. Function must have type annotations and docstring.

def resource(self, uri: str, mime_type: str = "text/plain", size: int = 1024) -> Callable

Decorator to register a function as an MCP resource or resource template. Use {param} in URI for templates.

def prompt(self, func: Callable) -> Callable

Decorator to register a function as an MCP prompt. Function should return a string or list of PromptMessage objects.

def run(self)

Start the server. Behavior depends on transport type.

Host

class Host:
    def __init__(
        self,
        servers: list[str],
        model: str = "gpt",
        preferred_transport: transport_types = "stdio",
        console: Console = Console()
    )

Orchestration engine for managing multiple MCP servers.

Parameters:

• servers: List of server names to connect to
• model: Model identifier for LLM
• preferred_transport: Transport type preference ("stdio", "direct", "sse")
• console: Rich console for output

Key Methods:

def agent_query(self, prompt: str, message_store: MessageStore = MessageStore()) -> str | None

Execute an agent loop that handles MCP tool calls. Returns final answer or None.

Client

class Client:
    def __init__(
        self,
        name: str = "Generic Client",
        transport: str | Transport | StdioClientTransport = "DirectTransport",
        server_function: Optional[Callable] = None
    )

MCP client for connecting to servers.

Key Methods:

def initialize(self)

Perform MCP handshake and capability discovery.

def send_request(self, request: MCPRequest) -> MCPResult

Send a request to the server and return the result.

def send_notification(self, notification: MCPNotification)

Send a notification to the server (no response expected).

MCPChat

class MCPChat(Chat):
    def __init__(
        self,
        servers: list[str],
        model: str = "gpt",
        preferred_transport: transport_types = "stdio",
        **kwargs
    )

Chat interface with MCP capabilities. Inherits from Chain's Chat class.

Parameters:

• servers: List of MCP server names to connect to
• model: Model identifier
• preferred_transport: Transport type preference

Additional Commands:

• /status: Show MCP connection status
• /list_tools: List available tools
• /list_resources: List available resources
• /list_prompts: List available prompts

Transport Classes

class StdioClientTransport(Transport):
    def __init__(self, server_command: list[str])

Client transport for subprocess communication via stdio.

class StdioServerTransport(Transport):
    def __init__(self)

Server transport for stdio communication.

class DirectTransport(Transport):
    def __init__(self, server_function: Callable)

In-process transport that directly calls server functions.

Usage Examples

Creating an MCP Server

from valve.mcplite.mcplite import MCPLite
from valve.transport import StdioServerTransport

mcp = MCPLite(transport=StdioServerTransport())

@mcp.tool
def add_numbers(a: int, b: int) -> int:
    """Add two numbers together."""
    return a + b

@mcp.resource(uri="myapp://status")
def get_status() -> str:
    """Get application status."""
    return "Server is running"

@mcp.prompt
def analysis_prompt(topic: str) -> str:
    """Generate an analysis prompt for a given topic."""
    return f"Please analyze the following topic in detail: {topic}"

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

Using Host to Orchestrate Multiple Servers

from valve.host.Host import Host
from Chain import MessageStore

# Connect to multiple MCP servers
host = Host(
    model="gpt",
    servers=["fetch", "obsidian"],
    preferred_transport="stdio"
)

# Execute a query that may use multiple tools
message_store = MessageStore()
result = host.agent_query(
    "Fetch the content from example.com and save it to my notes",
    message_store
)
print(result)

Building a Chat Application with MCP

from valve.mcpchat.mcpchat import MCPChat

# Create chat with MCP capabilities
chat = MCPChat(
    model="gpt",
    servers=["fetch", "obsidian"],
    preferred_transport="direct"
)

# Start interactive chat
chat.chat()

# Or use programmatically
response = chat.query("What's the weather in San Francisco?")