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‎docs/spec/_index.md‎ renamed to ‎docs/_index.md‎

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_**NOTE:** This is a very early draft. Feel free to discuss changes, requirements, etc._
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# Goal
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The Model Context Protocol (MCP) is an attempt to allow implementors to provide context to various LLM surfaces such as editors/IDEs, [claude.ai](https://claude.ai), etc., in a pluggable way. It separates the concerns of providing context from the LLM loop and its usage within.
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The Model Context Protocol (MCP) is an attempt to allow implementors to provide context to various LLM surfaces such as IDEs, [Claude Desktop](https://claude.ai/download) and others, in a pluggable way. It separates the concerns of providing context from the LLM loop and its usage within.
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This makes it **much** easier for anyone to script LLM applications for accomplishing their custom workflows, without the application needing to directly offer a large number of integrations.
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‎docs/architecture/_index.md‎

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---
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title: Architecture
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cascade:
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type: docs
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weight: 1
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---
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The Model Context Protocol (MCP) follows a client-host-server architecture where each host can run multiple client instances. This architecture enables users to integrate AI capabilities across applications while maintaining clear security boundaries and isolating concerns. Built on JSON-RPC, MCP provides a stateful session protocol focused on context exchange and sampling coordination between clients and servers.
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## Core Components
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```mermaid
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graph TB
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subgraph "Application Host Process"
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H[Host]
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C1[Client 1]
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C2[Client 2]
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C3[Client 3]
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H --> C1
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H --> C2
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H --> C3
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end
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S1[Server 1<br>Files & Git]
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S2[Server 2<br>Database]
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S3[Server 3<br>External APIs]
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C1 --> S1
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C2 --> S2
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C3 --> S3
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```
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### Host
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The host process acts as the container and coordinator:
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- Creates and manages multiple client instances
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- Controls client connection permissions and lifecycle
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- Enforces security policies and consent requirements
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- Handles user authorization decisions
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- Coordinates AI/LLM integration and sampling
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- Manages context aggregation across clients
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### Clients
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Each client maintains an isolated server connection:
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- Establishes one stateful session per server
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- Handles protocol negotiation and capability exchange
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- Routes protocol messages bidirectionally
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- Manages subscriptions and notifications
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- Maintains security boundaries between servers
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### Servers
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Servers provide specialized context and capabilities:
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- Expose resources, tools and prompts via MCP primitives
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- Operate independently with focused responsibilities
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- Request sampling through client interfaces
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- Must respect security constraints
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- Can be local processes or remote services
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## Protocol Capabilities and Flow
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The Model Context Protocol uses a capability-based negotiation system where clients and servers explicitly declare their supported features during initialization. Capabilities determine which protocol features and primitives are available during a session.
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- Servers declare capabilities like resource subscriptions, tool support, and prompt templates
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- Clients declare capabilities like sampling support and notification handling
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- Both parties must respect declared capabilities throughout the session
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- Additional capabilities can be negotiated through protocol extensions
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```mermaid
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sequenceDiagram
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participant Host
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participant Client
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participant Server
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Host->>Client: Initialize client
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Client->>Server: Initialize session with capabilities
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Server-->>Client: Negotiate supported capabilities
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Note over Host,Server: Active Session with Negotiated Features
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alt Server Request (if sampling capable)
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Server->>Client: Request (sampling)
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Client->>Host: Forward to AI
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Host-->>Client: AI response
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Client-->>Server: Response
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else Client Request (based on server caps)
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Client->>Server: Request (tools/resources)
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Server-->>Client: Response
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else Notifications (if supported)
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Server--)Client: Resource updates
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Client--)Server: Status changes
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end
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Host->>Client: Terminate
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Client->>Server: End session
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```
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Each capability unlocks specific protocol features for use during the session. For example:
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- Resource subscriptions require the server to declare subscription support
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- Tool invocation requires the server to declare tool capabilities
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- Sampling requires the client to declare sampling support
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This capability negotiation ensures clients and servers have a clear understanding of supported functionality while maintaining protocol extensibility.
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### Message Types
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MCP defines three core message types based on [JSON-RPC 2.0](https://www.jsonrpc.org/specification):
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- **Requests**: Bidirectional messages with method and parameters expecting a response
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- **Responses**: Results or errors matching specific request IDs
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- **Notifications**: One-way messages requiring no response
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Each message type follows the JSON-RPC 2.0 specification for structure and delivery semantics.
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## Protocol Features
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### Server Features
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Servers implement several foundational features that provide context and capabilities to clients:
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- **Resources**: Structured data or content exposed via URIs that can be read and optionally subscribed to for updates
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- **Prompts**: Pre-defined templates or instructions that guide language model interactions
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- **Tools**: Executable functions that allow models to perform actions or retrieve information
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- **Utilities**: Helper features for logging, argument completion, and other ancillary functions
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The server features focus on exposing data and functionality in a controlled way while maintaining security boundaries.
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### Client Features
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Clients provide core features for interacting with servers and coordinating with hosts:
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- **Sampling**: Ability to request and control language model interactions
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- **Root Directory Access**: Controlled exposure of filesystem locations to servers
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The client features emphasize safe integration of server capabilities while protecting user privacy and security.

‎docs/basic/_index.md‎

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---
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title: Base Protocol
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cascade:
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type: docs
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weight: 2
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---
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The Model Context Protocol (MCP) defines a set of JSON-RPC methods for communication between clients and servers in AI-assisted applications. MCP uses [JSON-RPC 2.0](https://www.jsonrpc.org/specification) as its base protocol.
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All messages in MCP **MUST** follow the [JSON-RPC 2.0](https://www.jsonrpc.org/specification) specification. The protocol defines three fundamental types of messages:
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| Type | Description | Requirements |
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|----------------|----------------------------------------|---------------------------------------|
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| `Requests` | Messages sent to initiate an operation | Must include unique ID and method name|
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| `Responses` | Messages sent in reply to requests | Must include same ID as request |
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| `Notifications`| One-way messages with no reply | Must not include an ID |
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The Model Context Protocol consists of several key components that work together:
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**Protocol Layers:**
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- **Base Protocol**: Core JSON-RPC message types and fundamental operations such as capability exchange
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- **Lifecycle Management**: Connection initialization, capability negotiation, and session control
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- **Server Features**: Resources, prompts, and tools exposed by servers
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- **Client Features**: Sampling and root directory capabilities
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- **Utilities**: Cross-cutting concerns like logging and argument completion
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All implementations **MUST** support the base protocol and lifecycle management components. Other components **MAY** be implemented based on the specific needs of the application.
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These protocol layers establish clear separation of concerns while enabling rich interactions between clients and servers. The modular design allows implementations to support exactly the features they need.
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### Model Context Protocol specific methods
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MCP defines methods based on JSON-RPC that clients and servers implement:
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{{< cards >}}
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{{< card link="lifecycle" title="Lifecycle" icon="refresh" >}}
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{{< card link="resources" title="Resources" icon="document" >}}
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{{< card link="prompts" title="Prompts" icon="chat-alt-2" >}}
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{{< card link="tools" title="Tools" icon="adjustments" >}}
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{{< card link="logging" title="Logging" icon="annotation" >}}
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{{< card link="sampling" title="Sampling" icon="code" >}}
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{{< /cards >}}
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### Authentication
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Authentication mechanisms are not part of the core MCP specification. Implementations **MAY** provide authentication based on the transport they use.
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## Specification
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The official specification can be found in [TypeScript source](http://github.com/modelcontextprotocol/specification/tree/main/schema/schema.ts) and [JSON Schema](http://github.com/modelcontextprotocol/specification/tree/main/schema/schema.json) formats. The TypeScript version serves as the source of truth, while the JSON Schema version is generated from it.

‎docs/basic/lifecycle.md‎

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---
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title: Lifecycle
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type: docs
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weight: 30
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---
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{{< callout type="info" >}}
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**Protocol Revision**: 2024-11-05 (Final)
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{{< /callout >}}
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The Model Context Protocol (MCP) defines a rigorous lifecycle for client-server connections that ensures proper capability negotiation and state management. This lifecycle consists of four distinct phases:
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1. **Initialization**: Capability negotiation and protocol version agreement
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2. **Ready**: Final confirmation before beginning operations
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3. **Operation**: Normal protocol communication
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4. **Shutdown**: Graceful termination of the connection
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```mermaid
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sequenceDiagram
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participant Client
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participant Server
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Note over Client,Server: Initialization Phase
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Client->>Server: initialize request
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Server-->>Client: initialize response
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Client--)Server: initialized notification
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Note over Client,Server: Operation Phase
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activate Client
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activate Server
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rect rgb(200, 220, 250)
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note over Client,Server: Normal protocol operations
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end
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deactivate Client
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deactivate Server
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Note over Client,Server: Shutdown Phase
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Client->>Server: shutdown request
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Server-->>Client: shutdown response
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Note over Client,Server: Connection closed
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```
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## Lifecycle Phases
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### 1. Initialization Phase
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The initialization phase MUST be the first interaction between client and server. During this phase, the client and server:
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- Establish protocol version compatibility
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- Exchange and negotiate capabilities
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- Share implementation details
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The client MUST initiate this phase by sending an `initialize` request containing:
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- Protocol version supported
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- Client capabilities
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- Client implementation information
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```json
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{
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"jsonrpc": "2.0",
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"id": 1,
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"method": "initialize",
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"params": {
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"protocolVersion": "2024-11-05",
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"capabilities": {
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"roots": {
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"listChanged": true
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},
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"sampling": {}
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},
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"clientInfo": {
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"name": "ExampleClient",
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"version": "1.0.0"
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}
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}
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}
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```
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The server MUST respond with its own capabilities and information:
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```json
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{
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"jsonrpc": "2.0",
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"id": 1,
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"result": {
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"protocolVersion": "2024-11-05",
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"capabilities": {
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"prompts": {
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"listChanged": true
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},
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"resources": {
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"subscribe": true,
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"listChanged": true
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},
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"tools": {
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"listChanged": true
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}
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},
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"serverInfo": {
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"name": "ExampleServer",
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"version": "1.0.0"
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}
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}
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}
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```
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#### Capability Negotiation
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The initialization phase establishes which optional protocol features will be available during the session. Key capabilities include:
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| Category | Capability | Description |
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|---------------|---------------|-----------------------------------------------|
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| Client | `roots` | Ability to provide filesystem roots |
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| Client | `sampling` | Support for LLM sampling requests |
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| Client | `experimental`| Support for non-standard experimental features|
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| Server | `prompts` | Offers prompt templates |
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| Server | `resources` | Provides readable resources |
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| Server | `tools` | Exposes callable tools |
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| Server | `logging` | Support for structured log messages |
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| Server | `experimental`| Support for non-standard experimental features|
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Capabilities can include sub-capabilities like:
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- `listChanged`: Support for list change notifications (for prompts, resources, and tools)
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- `subscribe`: Support for subscriptions (resources only)
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### 2. Ready Phase
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After successful initialization, the client MUST send an `initialized` notification to indicate it is ready to begin normal operations:
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```json
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{
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"jsonrpc": "2.0",
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"method": "initialized"
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}
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```
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The server MUST NOT send any protocol messages besides the initialization response until it receives this notification.
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### 3. Operation Phase
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During the operation phase, the client and server exchange messages according to the negotiated capabilities. Both parties MUST:
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- Respect the negotiated protocol version
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- Only use capabilities that were successfully negotiated
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- Handle messages according to the JSON-RPC 2.0 specification
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### 4. Shutdown Phase
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The shutdown phase cleanly terminates the protocol connection. No specific shutdown messages are defined - instead, the underlying transport mechanism should be used to signal connection termination:
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- For STDIO-based transport, the MCP server process should be terminated
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- For HTTP-based transport, the HTTP connection should be closed
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## Error Handling
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Implementations MUST handle these error cases:
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- Protocol version mismatch
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- Required capability negotiation failure
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- Initialize request timeout
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- Shutdown request timeout
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Server implementations are SHOULD implement appropriate timeouts for all lifecycle phases to prevent hung connections and resource exhaustion.
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When errors occur during initialization, the server MUST respond with an appropriate error code and SHOULD close the connection.
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Example initialization error:
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```json
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{
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"jsonrpc": "2.0",
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"id": 1,
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"error": {
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"code": -32600,
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"message": "Unsupported protocol version",
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"data": {
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"supported": ["2024-11-05"],
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"requested": "1.0.0"
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}
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}
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}
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```

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