Resources

specification/2024-11-05/server/resources New page · 357 lines, new page

# Resources ## User Interaction Model ## Capabilities ## Protocol Messages ### Listing Resources ### Reading Resources ### Resource Templates ### List Changed Notification ### Subscriptions ## Message Flow ## Data Types ### Resource ### Resource Contents #### Text Content #### Binary Content ## Common URI Schemes ### https\:// ### file:// ### git:// ## Error Handling ## Security Considerations

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# Resources

The Model Context Protocol (MCP) provides a standardized way for servers to expose
resources to clients. Resources allow servers to share data that provides context to
language models, such as files, database schemas, or application-specific information.
Each resource is uniquely identified by a
[URI](https://datatracker.ietf.org/doc/html/rfc3986).

## User Interaction Model

Resources in MCP are designed to be **application-driven**, with host applications
determining how to incorporate context based on their needs.

For example, applications could:

* Expose resources through UI elements for explicit selection, in a tree or list view
* Allow the user to search through and filter available resources
* Implement automatic context inclusion, based on heuristics or the AI model's selection

<img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/specification/2024-11-05/server/resource-picker.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=c393fd9aa41eca521cb2f830d839612f" alt="Example of resource context picker" width="174" height="181" data-path="specification/2024-11-05/server/resource-picker.png" />

However, implementations are free to expose resources through any interface pattern that
suits their needs—the protocol itself does not mandate any specific user
interaction model.

## Capabilities

Servers that support resources **MUST** declare the `resources` capability:

```json theme={null}
{
  "capabilities": {
    "resources": {
      "subscribe": true,
      "listChanged": true
    }
  }
}
```

The capability supports two optional features:

* `subscribe`: whether the client can subscribe to be notified of changes to individual
  resources.
* `listChanged`: whether the server will emit notifications when the list of available
  resources changes.

Both `subscribe` and `listChanged` are optional—servers can support neither,
either, or both:

```json theme={null}
{
  "capabilities": {
    "resources": {} // Neither feature supported
  }
}
```

```json theme={null}
{
  "capabilities": {
    "resources": {
      "subscribe": true // Only subscriptions supported
    }
  }
}
```

```json theme={null}
{
  "capabilities": {
    "resources": {
      "listChanged": true // Only list change notifications supported
    }
  }
}
```

## Protocol Messages

### Listing Resources

To discover available resources, clients send a `resources/list` request. This operation
supports
[pagination](/specification/2024-11-05/server/utilities/pagination).

**Request:**

```json theme={null}
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "resources/list",
  "params": {
    "cursor": "optional-cursor-value"
  }
}
```

**Response:**

```json theme={null}
{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "resources": [
      {
        "uri": "file:///project/src/main.rs",
        "name": "main.rs",
        "description": "Primary application entry point",
        "mimeType": "text/x-rust"
      }
    ],
    "nextCursor": "next-page-cursor"
  }
}
```

### Reading Resources

To retrieve resource contents, clients send a `resources/read` request:

**Request:**

```json theme={null}
{
  "jsonrpc": "2.0",
  "id": 2,
  "method": "resources/read",
  "params": {
    "uri": "file:///project/src/main.rs"
  }
}
```

**Response:**

```json theme={null}
{
  "jsonrpc": "2.0",
  "id": 2,
  "result": {
    "contents": [
      {
        "uri": "file:///project/src/main.rs",
        "mimeType": "text/x-rust",
        "text": "fn main() {\n    println!(\"Hello world!\");\n}"
      }
    ]
  }
}
```

### Resource Templates

Resource templates allow servers to expose parameterized resources using
[URI templates](https://datatracker.ietf.org/doc/html/rfc6570). Arguments may be
auto-completed through [the completion API](/specification/2024-11-05/server/utilities/completion).
This operation supports
[pagination](/specification/2024-11-05/server/utilities/pagination).

**Request:**

```json theme={null}
{
  "jsonrpc": "2.0",
  "id": 3,
  "method": "resources/templates/list",
  "params": {
    "cursor": "optional-cursor-value"
  }
}
```

**Response:**

```json theme={null}
{
  "jsonrpc": "2.0",
  "id": 3,
  "result": {
    "resourceTemplates": [
      {
        "uriTemplate": "file:///{path}",
        "name": "Project Files",
        "description": "Access files in the project directory",
        "mimeType": "application/octet-stream"
      }
    ],
    "nextCursor": "next-page-cursor"
  }
}
```

### List Changed Notification

When the list of available resources changes, servers that declared the `listChanged`
capability **SHOULD** send a notification:

```json theme={null}
{
  "jsonrpc": "2.0",
  "method": "notifications/resources/list_changed"
}
```

### Subscriptions

The protocol supports optional subscriptions to resource changes. Clients can subscribe
to specific resources and receive notifications when they change:

**Subscribe Request:**

```json theme={null}
{
  "jsonrpc": "2.0",
  "id": 4,
  "method": "resources/subscribe",
  "params": {
    "uri": "file:///project/src/main.rs"
  }
}
```

**Update Notification:**

```json theme={null}
{
  "jsonrpc": "2.0",
  "method": "notifications/resources/updated",
  "params": {
    "uri": "file:///project/src/main.rs"
  }
}
```

## Message Flow

```mermaid theme={null}
sequenceDiagram
    participant Client
    participant Server

    Note over Client,Server: Resource Discovery
    Client->>Server: resources/list
    Server-->>Client: List of resources

    Note over Client,Server: Resource Access
    Client->>Server: resources/read
    Server-->>Client: Resource contents

    Note over Client,Server: Subscriptions
    Client->>Server: resources/subscribe
    Server-->>Client: Subscription confirmed

    Note over Client,Server: Updates
    Server--)Client: notifications/resources/updated
    Client->>Server: resources/read
    Server-->>Client: Updated contents
```

## Data Types

### Resource

A resource definition includes:

* `uri`: Unique identifier for the resource
* `name`: Human-readable name
* `description`: Optional description
* `mimeType`: Optional MIME type

### Resource Contents

Resources can contain either text or binary data:

#### Text Content

```json theme={null}
{
  "uri": "file:///example.txt",
  "mimeType": "text/plain",
  "text": "Resource content"
}
```

#### Binary Content

```json theme={null}
{
  "uri": "file:///example.png",
  "mimeType": "image/png",
  "blob": "base64-encoded-data"
}
```

## Common URI Schemes

The protocol defines several standard URI schemes. This list not

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