# MCP Specification 2025-06-18
Core MCP specification version with all fundamental features.
## Version Information
- **Release Date**: June 18, 2025
- **Status**: Stable (superseded by 2025-11-25)
- **Schema**: `https://modelcontextprotocol.io/schema/2025-06-18/schema.json`
## Overview
This is the core MCP specification that establishes all fundamental protocol features:
- Complete Tools, Resources, and Prompts support
- Client capabilities (Sampling, Roots)
- Utilities (Logging, Progress, Completion, Cancellation)
- Full content type support
## Core Features
### Server Features
- **Tools** - Executable functions for LLMs
- **Resources** - Data and context access
- **Prompts** - Templated messages and workflows
### Client Features
- **Sampling** - Server-initiated LLM interactions
- **Roots** - Filesystem/URI boundary queries
### Utilities
- **Logging** - Configurable logging with multiple levels
- **Progress** - Progress tracking for long operations
- **Completion** - Argument autocompletion
- **Cancellation** - Request cancellation support
## Reference Implementation
All features from this specification are fully implemented in the reference server.
**Primary Example**: `examples/11_full_server.py`
## Specification Structure
### Base Protocol
- JSON-RPC 2.0 messaging
- Request/Response pattern
- Notifications (fire-and-forget)
- Error handling
### Lifecycle
1. Client sends `initialize` with capabilities
2. Server responds with server capabilities
3. Client sends `initialized` notification
4. Normal operation (tools, resources, prompts)
5. Bidirectional `ping` for health checks
### Message Flow
```
Client Server
| |
|------ initialize (capabilities) ----->|
| |
|<----- response (capabilities) ---------|
| |
|------ initialized (notification) ---->|
| |
|------ tools/list ------------------->|
|<----- response (tools) ---------------|
| |
|------ tools/call ------------------->|
|<----- response (result) --------------|
| |
|<----- notifications/message ----------|
| |
```
## Capabilities Example
### Server Capabilities
```json
{
"capabilities": {
"tools": {
"listChanged": true
},
"resources": {
"subscribe": true,
"listChanged": true
},
"prompts": {
"listChanged": true
},
"logging": {}
}
}
```
### Client Capabilities
```json
{
"capabilities": {
"sampling": {},
"roots": {
"listChanged": true
}
}
}
```
## Content Types
All content types defined in this specification:
### TextContent
```json
{
"type": "text",
"text": "Content here"
}
```
### ImageContent
```json
{
"type": "image",
"data": "base64-encoded-data",
"mimeType": "image/png"
}
```
### EmbeddedResource
```json
{
"type": "resource",
"resource": {
"uri": "file:///path/to/file",
"mimeType": "text/plain",
"text": "Content"
}
}
```
## Specification Links
- [Official Spec](https://modelcontextprotocol.io/specification/2025-06-18)
- [Schema](https://github.com/modelcontextprotocol/specification/tree/main/schema/2025-06-18)
- [Tools](https://modelcontextprotocol.io/specification/2025-06-18/server/tools)
- [Resources](https://modelcontextprotocol.io/specification/2025-06-18/server/resources)
- [Prompts](https://modelcontextprotocol.io/specification/2025-06-18/server/prompts)
## Migration
### From 2024-11-05
The 2025-06-18 specification adds:
- Enhanced prompt support with arguments
- Resource templates and subscriptions
- Progress notifications
- Completion support
- Improved error handling
### To 2025-11-25
The 2025-11-25 specification adds:
- Tasks abstraction
- Enterprise IdP support
Both migrations are backward compatible.
## Feature Checklist
See [features.md](./features.md) for complete feature checklist.
