Protocol Revision: 2024-11-05
All messages between MCP clients and servers MUST follow the JSON-RPC 2.0 specification. The protocol defines three fundamental types of messages:
TypeDescriptionRequirements
RequestsMessages sent to initiate an operationMust include unique ID and method name
ResponsesMessages sent in reply to requestsMust include same ID as request
NotificationsOne-way messages with no replyMust not include an ID
Responses are further sub-categorized as either successful results or errors. Results can follow any JSON object structure, while errors must include an error code and message at minimum.

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Protocol Layers

The Model Context Protocol consists of several key components that work together:
  • Base Protocol: Core JSON-RPC message types
  • Lifecycle Management: Connection initialization, capability negotiation, and session control
  • Server Features: Resources, prompts, and tools exposed by servers
  • Client Features: Sampling and root directory lists provided by clients
  • Utilities: Cross-cutting concerns like logging and argument completion
All implementations MUST support the base protocol and lifecycle management components. Other components MAY be implemented based on the specific needs of the application. 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. See the following pages for more details on the different components:

Lifecycle

Resources

Prompts

Tools

Logging

Sampling

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Auth

Authentication and authorization are not currently part of the core MCP specification, but we are considering ways to introduce them in future. Join us in GitHub Discussions to help shape the future of the protocol! Clients and servers MAY negotiate their own custom authentication and authorization strategies.

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Schema

The full specification of the protocol is defined as a TypeScript schema. This is the source of truth for all protocol messages and structures. There is also a JSON Schema, which is automatically generated from the TypeScript source of truth, for use with various automated tooling.