Add QR code Python MCP server example

examples/qr-server/.gitignore

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+# Python virtual environment
+.venv/
+venv/
+env/
+
+# Python cache
+__pycache__/
+*.py[cod]
+*$py.class
+*.so
+
+# Distribution / packaging
+dist/
+build/
+*.egg-info/
+
+# IDE
+.idea/
+.vscode/
+*.swp
+*.swo
+
+# OS
+.DS_Store
+Thumbs.db

examples/qr-server/README.md

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+# QR Code MCP Server
+
+A minimal Python MCP server that generates customizable QR codes with an interactive widget UI.
+
+![Screenshot](https://modelcontextprotocol.github.io/ext-apps/screenshots/qr-server/screenshot.png)
+
+## Features
+
+- Generate QR codes from any text or URL
+- Customizable colors, size, and error correction
+- Interactive widget that displays in MCP-UI enabled clients
+- Supports both HTTP (for web clients) and stdio (for Claude Desktop)
+
+## Quick Start
+
+```bash
+# Create virtual environment
+python3 -m venv .venv
+source .venv/bin/activate
+
+# Install dependencies
+pip install -r requirements.txt
+
+# Run server (HTTP mode)
+python server.py
+# → QR Server listening on http://localhost:3108/mcp
+```
+
+## Usage
+
+### HTTP Mode (for basic-host / web clients)
+
+```bash
+python server.py
+```
+
+Connect from basic-host:
+
+```bash
+SERVERS='["http://localhost:3108/mcp"]' bun serve.ts
+```
+
+### Stdio Mode (for Claude Desktop)
+
+```bash
+python server.py --stdio
+```
+
+Add to Claude Desktop config (`~/Library/Application Support/Claude/claude_desktop_config.json`):
+
+```json
+{
+  "mcpServers": {
+    "qr": {
+      "command": "/path/to/qr-server/.venv/bin/python",
+      "args": ["/path/to/qr-server/server.py", "--stdio"]
+    }
+  }
+}
+```
+
+### Docker (accessing host server from container)
+
+```
+http://host.docker.internal:3108/mcp
+```
+
+## Tool: `generate_qr`
+
+Generate a QR code with optional customization.
+
+### Parameters
+
+| Parameter          | Type   | Default    | Description                     |
+| ------------------ | ------ | ---------- | ------------------------------- |
+| `text`             | string | (required) | The text or URL to encode       |
+| `box_size`         | int    | 10         | Size of each box in pixels      |
+| `border`           | int    | 4          | Border size in boxes            |
+| `error_correction` | string | "M"        | Error correction level: L/M/Q/H |
+| `fill_color`       | string | "black"    | Foreground color (hex or name)  |
+| `back_color`       | string | "white"    | Background color (hex or name)  |
+
+### Error Correction Levels
+
+| Level | Recovery | Use Case                  |
+| ----- | -------- | ------------------------- |
+| L     | 7%       | Clean environments        |
+| M     | 15%      | General use (default)     |
+| Q     | 25%      | Industrial/outdoor        |
+| H     | 30%      | Adding logos/damage-prone |
+
+### Example Inputs
+
+**Basic:**
+
+```json
+{ "text": "https://example.com" }
+```
+
+**Styled:**
+
+```json
+{
+  "text": "https://claude.ai",
+  "fill_color": "#CC785C",
+  "back_color": "#FFF8F5",
+  "box_size": 12,
+  "border": 3
+}
+```
+
+**Dark Mode:**
+
+```json
+{
+  "text": "Hello World",
+  "fill_color": "#E0E0E0",
+  "back_color": "#1a1a1a",
+  "box_size": 15,
+  "border": 2
+}
+```
+
+**WiFi QR Code:**
+
+```json
+{
+  "text": "WIFI:T:WPA;S:MyNetwork;P:MyPassword;;",
+  "error_correction": "H",
+  "box_size": 10
+}
+```
+
+## Architecture
+
+```
+qr-server/
+├── server.py      # MCP server (FastMCP + uvicorn)
+├── widget.html    # Interactive UI widget
+├── requirements.txt
+└── README.md
+```
+
+### Protocol
+
+The widget uses MCP Apps SDK protocol:
+
+1. Widget sends `ui/initialize` request
+2. Host responds with capabilities
+3. Widget sends `ui/notifications/initialized`
+4. Host sends `ui/notifications/tool-result` with QR image
+5. Widget renders image and sends `ui/notifications/size-changed`
+
+## Dependencies
+
+- `mcp[cli]` - MCP Python SDK with FastMCP
+- `qrcode[pil]` - QR code generation with Pillow
+- `uvicorn` - ASGI server (included with mcp)
+- `starlette` - CORS middleware (included with mcp)
+
+## License
+
+MIT

examples/qr-server/requirements.txt

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+mcp[cli]>=1.0.0
+qrcode[pil]>=7.4

examples/qr-server/server.py

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+"""
+QR Code MCP Server - Generates QR codes from text
+"""
+import os
+import sys
+import io
+import base64
+from pathlib import Path
+
+import qrcode
+import uvicorn
+from mcp.server.fastmcp import FastMCP
+from mcp.types import ImageContent
+from starlette.middleware.cors import CORSMiddleware
+
+WIDGET_URI = "ui://qr-server/widget.html"
+HOST = os.environ.get("HOST", "0.0.0.0")  # 0.0.0.0 for Docker compatibility
+PORT = int(os.environ.get("PORT", "3108"))
+
+mcp = FastMCP("QR Server", port=PORT, stateless_http=True)
+
+
+@mcp.tool(meta={"ui/resourceUri": WIDGET_URI})
+def generate_qr(
+    text: str,
+    box_size: int = 10,
+    border: int = 4,
+    error_correction: str = "M",
+    fill_color: str = "black",
+    back_color: str = "white",
+) -> list[ImageContent]:
+    """Generate a QR code from text.
+
+    Args:
+        text: The text/URL to encode
+        box_size: Size of each box in pixels (default: 10)
+        border: Border size in boxes (default: 4)
+        error_correction: Error correction level - L(7%), M(15%), Q(25%), H(30%)
+        fill_color: Foreground color (hex like #FF0000 or name like red)
+        back_color: Background color (hex like #FFFFFF or name like white)
+    """
+    error_levels = {
+        "L": qrcode.constants.ERROR_CORRECT_L,
+        "M": qrcode.constants.ERROR_CORRECT_M,
+        "Q": qrcode.constants.ERROR_CORRECT_Q,
+        "H": qrcode.constants.ERROR_CORRECT_H,
+    }
+
+    qr = qrcode.QRCode(
+        version=1,
+        error_correction=error_levels.get(error_correction.upper(), qrcode.constants.ERROR_CORRECT_M),
+        box_size=box_size,
+        border=border,
+    )
+    qr.add_data(text)
+    qr.make(fit=True)
+
+    img = qr.make_image(fill_color=fill_color, back_color=back_color)
+    buffer = io.BytesIO()
+    img.save(buffer, format="PNG")
+    b64 = base64.b64encode(buffer.getvalue()).decode()
+    return [ImageContent(type="image", data=b64, mimeType="image/png")]
+
+
+# IMPORTANT: resourceDomains needed for CSP to allow loading SDK from unpkg.com
+# Without this, hosts enforcing CSP will block the external script import
+@mcp.resource(WIDGET_URI, mime_type="text/html")
+def widget() -> dict:
+    html = Path(__file__).parent.joinpath("widget.html").read_text()
+    return {
+        "text": html,
+        "_meta": {
+            "ui": {
+                "csp": {
+                    "resourceDomains": ["https://unpkg.com"]
+                }
+            }
+        }
+    }
+
+# HACK: Bypass SDK's restrictive mime_type validation
+# The SDK pattern doesn't allow ";profile=mcp-app" but MCP spec requires it for widgets
+# https://github.com/modelcontextprotocol/python-sdk/pull/1755
+for resource in mcp._resource_manager._resources.values():
+    if str(resource.uri) == WIDGET_URI:
+        object.__setattr__(resource, 'mime_type', 'text/html;profile=mcp-app')
+
+if __name__ == "__main__":
+    if "--stdio" in sys.argv:
+        # Claude Desktop mode
+        mcp.run(transport="stdio")
+    else:
+        # HTTP mode for basic-host (default) - with CORS
+        app = mcp.streamable_http_app()
+        app.add_middleware(
+            CORSMiddleware,
+            allow_origins=["*"],
+            allow_methods=["*"],
+            allow_headers=["*"],
+        )
+        print(f"QR Server listening on http://{HOST}:{PORT}/mcp")
+        uvicorn.run(app, host=HOST, port=PORT)

examples/qr-server/widget.html

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+<!DOCTYPE html>
+<html>
+<head>
+  <style>
+    html, body {
+      margin: 0;
+      padding: 0;
+      overflow: hidden;
+      background: transparent;
+    }
+    body {
+      display: flex;
+      justify-content: center;
+      align-items: center;
+      height: 340px;
+      width: 340px;
+    }
+    img {
+      width: 300px;
+      height: 300px;
+      border-radius: 8px;
+      box-shadow: 0 2px 8px rgba(0,0,0,0.1);
+    }
+  </style>
+</head>
+<body>
+  <div id="qr"></div>
+  <script type="module">
+    import { App, PostMessageTransport } from "https://unpkg.com/@modelcontextprotocol/ext-apps@0.0.4";
+
+    const app = new App({ name: "QR Widget", version: "1.0.0" });
+
+    app.ontoolresult = ({ content }) => {
+      const img = content?.find(c => c.type === 'image');
+      if (img) {
+        const qrDiv = document.getElementById('qr');
+        qrDiv.innerHTML = '';
+
+        const allowedTypes = ['image/png', 'image/jpeg', 'image/gif'];
+        const mimeType = allowedTypes.includes(img.mimeType) ? img.mimeType : 'image/png';
+
+        const image = document.createElement('img');
+        image.src = `data:${mimeType};base64,${img.data}`;
+        image.alt = "QR Code";
+        qrDiv.appendChild(image);
+      }
+    };
+
+    await app.connect(new PostMessageTransport(window.parent));
+  </script>
+</body>
+</html>