All messages between MCP clients and servers MUST follow the
JSON-RPC 2.0 specification. The protocol defines
three fundamental types of messages:
Type
Description
Requirements
Requests
Messages sent to initiate an operation
Must include unique ID and method name
Responses
Messages sent in reply to requests
Must include same ID as request
Notifications
One-way messages with no reply
Must 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.
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:
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.
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.
