---
title: "Resources"
description: "Define and expose resources from your MCP server"
icon: "file"
---

Resources expose data to MCP clients. Unlike tools (which perform actions), resources provide read-only access to content like files, database records, or live data.

## Example

```python
@server.resource(
    uri="config://{section}",
    name="app_config",
    title="Application Config",
    description="Get configuration for a specific section",
    mime_type="application/json",
)
def get_config(section: str) -> str:
    """Get configuration for a specific section."""
    configs = {
        "database": '{"host": "localhost", "port": 5432}',
        "cache": '{"enabled": true, "ttl": 3600}',
    }
    return configs.get(section, '{"error": "Section not found"}')
```

## Anatomy of a Resource

When a client calls `resources/list`, the server returns metadata for each resource. Resources with URI templates (like `{section}`) are returned via `resources/templates/list` instead.

Here's the JSON-RPC response that the example above produces when a client calls `resources/templates/list`:

```json
{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "resourceTemplates": [
      {
        "uriTemplate": "config://{section}",
        "name": "app_config",
        "title": "Application Config",
        "description": "Get configuration for a specific section",
        "mimeType": "application/json"
      }
    ]
  }
}
```

Here's what maps to what:

| Python | MCP Schema | Notes |
|--------|-----------|-------|
| `uri="config://{section}"` | `"uriTemplate"` | `{section}` makes it a template; without it, it would be a static `"uri"` |
| `name="app_config"` | `"name"` | Falls back to function name if omitted |
| `title="Application Config"` | `"title"` | Human-readable display name |
| `description="Get configuration..."` | `"description"` | Falls back to docstring if omitted |
| `mime_type="application/json"` | `"mimeType"` | Tells clients how to interpret the content |
| `section: str` | *(extracted from URI)* | Parameter matched from the URI template |

<Tip>
If your URI contains `{param}` placeholders, the resource is registered as a **template**. Otherwise, it's registered as a **static resource**.
</Tip>

## Static Resources

Resources without URI parameters are static — they always return at the same URI:

```python
from datetime import datetime

@server.resource(
    uri="time://current",
    name="current_time",
    title="Current Time",
    mime_type="text/plain",
)
def current_time() -> str:
    """Returns the current server time."""
    return datetime.now().isoformat()
```

## Resource Templates

Use `{param}` placeholders in the URI to create dynamic resources:

```python
@server.resource(
    uri="user://{user_id}",
    name="user_profile",
    title="User Profile",
    description="Get a user's profile by ID",
    mime_type="application/json",
)
def get_user(user_id: str) -> str:
    """Fetch user profile by ID."""
    users = {"1": "Alice", "2": "Bob"}
    name = users.get(user_id, "Unknown")
    return f'{{"id": "{user_id}", "name": "{name}"}}'
```

Clients request `user://123` and the function receives `user_id="123"`.

### Multiple Parameters

Templates support multiple parameters:

```python
@server.resource(
    uri="file://{folder}/{filename}",
    name="file_content",
    mime_type="text/plain",
)
def get_file(folder: str, filename: str) -> str:
    """Read a file from a folder."""
    return f"Content of {folder}/{filename}"
```

## Async Resources

Resources can be async for I/O operations:

```python
import httpx

@server.resource(
    uri="api://weather",
    mime_type="application/json",
)
async def weather_data() -> str:
    """Fetch current weather data."""
    async with httpx.AsyncClient() as client:
        response = await client.get("https://api.weather.com/current")
        return response.text
```

## Binary Resources

Return bytes for binary content:

```python
@server.resource(
    uri="image://logo",
    mime_type="image/png",
)
def logo_image() -> bytes:
    """Return the application logo."""
    with open("logo.png", "rb") as f:
        return f.read()
```

## Resource Subscriptions

Clients can subscribe to resources and receive notifications when they change. This follows the [MCP resource subscriptions spec](https://modelcontextprotocol.io/specification/2025-11-25/server/resources#subscriptions).

### How It Works

1. Client sends `resources/subscribe` with a resource URI
2. Your server updates the resource and calls `notify_resource_updated()`
3. All subscribed clients receive a `notifications/resources/updated` notification
4. Clients re-read the resource to get the new content

MCPServer handles subscribe/unsubscribe tracking automatically — you just need to call `notify_resource_updated()` when your resource changes.

### Example

```python
current_price = 100.0

@server.resource(uri="data://price", name="stock_price", mime_type="text/plain")
def get_price() -> str:
    return str(current_price)

@server.tool()
async def update_price(new_price: float) -> str:
    """Update the stock price and notify subscribers."""
    global current_price
    current_price = new_price
    await server.notify_resource_updated("data://price")
    return f"Price updated to {new_price}"
```

When a client subscribes to `data://price` and then any client calls `update_price`, all subscribers receive the notification and can re-read the resource.

<Note>
Subscriptions are session-scoped — they're automatically cleaned up when a client disconnects. If the server restarts, clients need to re-subscribe.
</Note>

## Common MIME Types

| MIME Type | Use Case |
|-----------|----------|
| `text/plain` | Plain text content |
| `application/json` | JSON data |
| `text/markdown` | Markdown documents |
| `text/html` | HTML content |
| `image/png` | PNG images |

## Resources vs Tools

| Aspect | Resources | Tools |
|--------|-----------|-------|
| Purpose | Expose data | Perform actions |
| Side effects | None (read-only) | May modify state |
| Caching | Can be cached | Generally not cached |
| Use case | Configuration, files, status | Operations, calculations |
