mark3labs/mcp-go

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That's it!
MCP Go handles all the complex protocol details and server management, so you can focus on building great tools. It aims to be high-level and easy to use.
Key features:
* **Fast**: High-level interface means less code and faster development
* **Simple**: Build MCP servers with minimal boilerplate
* **Complete***: MCP Go aims to provide a full implementation of the core MCP specification
(\*emphasis on *aims*)
🚨 🚧 🏗️ *MCP Go is under active development, as is the MCP specification itself. Core features are working but some advanced capabilities are still in progress.*
Table of Contents
- Installation
- Quickstart
- What is MCP?
- Core Concepts
- Server
- Resources
- Tools
- Prompts
- Examples
- Extras
- Transports
- OAuth Protected Resource Metadata
- Session Management
- Basic Session Handling
- Per-Session Tools
- Tool Filtering
- Working with Context
- Request Hooks
- Tool Handler Middleware
- Regenerating Server Code
Installation
Quickstart
Let's create a simple MCP server that exposes a calculator tool and some data:
What is MCP?
The Model Context Protocol (MCP) lets you build servers that expose data and functionality to LLM applications in a secure, standardized way. Think of it like a web API, but specifically designed for LLM interactions.
MCP servers can:
- Expose data through **Resources** (think of these sort of like GET endpoints; they are used to load information into the LLM's context)
- Provide functionality through **Tools** (sort of like POST endpoints; they are used to execute code or otherwise produce a side effect)
- Define interaction patterns through **Prompts** (reusable templates for LLM interactions)
- And more!
mcp-go implements the Model Context Protocol specification version 2025-11-25, with backward compatibility for versions 2025-06-18, 2025-03-26, and 2024-11-05.
Core Concepts
Server
Show Server Examples
The server is your core interface to the MCP protocol. It handles connection management, protocol compliance, and message routing:
Resources
Show Resource Examples
Resources are how you expose data to LLMs. They can be anything - files, API responses, database queries, system information, etc. Resources can be:
- Static (fixed URI)
- Dynamic (using URI templates)
Here's a simple example of a static resource:
And here's an example of a dynamic resource using a template:
The examples are simple but demonstrate the core concepts. Resources can be much more sophisticated - serving multiple contents, integrating with databases or external APIs, etc.
Tools
Show Tool Examples
Tools let LLMs take actions through your server. Unlike resources, tools are expected to perform computation and have side effects. They're similar to POST endpoints in a REST API.
Task-Augmented Tools
Task-augmented tools execute asynchronously and return results via polling. This is useful for long-running operations that would otherwise block or time out. Task tools support three modes:
- **TaskSupportForbidden** (default): The tool cannot be invoked as a task
- **TaskSupportOptional**: The tool can be invoked as a task or synchronously
- **TaskSupportRequired**: The tool must be invoked as a task
go
// Simple greeting prompt
s.AddPrompt(mcp.NewPrompt("greeting",
mcp.WithPromptDescription("A friendly greeting prompt"),
mcp.WithArgument("name",
mcp.ArgumentDescription("Name of the person to greet"),
),
), func(ctx context.Context, request mcp.GetPromptRequest) (*mcp.GetPromptResult, error) {
name := request.Params.Arguments["name"]
if name == "" {
name = "friend"
}
return mcp.NewGetPromptResult(
"A friendly greeting",
[]mcp.PromptMessage{
mcp.NewPromptMessage(
mcp.RoleAssistant,
mcp.NewTextContent(fmt.Sprintf("Hello, %s! How can I help you today?", name)),