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fastmcp/examples/apps/qr_server
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Jeremiah Lowin 8cf4506aa9
 Publish FastMCP 4 (alpha) docs to gofastmcp.com (#4624)
2026-07-23 21:21:01 -04:00
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fastmcp.json MCP Apps: structured CSP/permissions types, resource meta propagation fix, QR example (#3031) 2026-01-30 14:05:25 -05:00
pyproject.toml MCP Apps: structured CSP/permissions types, resource meta propagation fix, QR example (#3031) 2026-01-30 14:05:25 -05:00
qr_server.py Publish FastMCP 4 (alpha) docs to gofastmcp.com (#4624) 2026-07-23 21:21:01 -04:00
README.md Rename ui= to app= and consolidate ToolUI/ResourceUI into AppConfig (#3117) 2026-02-08 20:26:47 -05:00

README.md

QR Code MCP App

An MCP App server that generates QR codes with an interactive viewer UI. Ported from the ext-apps QR server example to demonstrate FastMCP's MCP Apps support.

What it demonstrates

  • Linking a tool to a ui:// resource via AppConfig
  • Serving embedded HTML with the @modelcontextprotocol/ext-apps JS SDK from CDN
  • Declaring CSP resource domains via ResourceCSP
  • Returning ImageContent (base64 PNG) from a tool

Setup

cd examples/apps/qr_server
uv sync

Usage

uv run python qr_server.py

Or install it into an MCP client:

fastmcp install stdio fastmcp.json

How it works

The server registers one tool (generate_qr) and one resource (ui://qr-server/view.html). The tool generates a QR code as a base64 PNG image. The resource serves an HTML page that uses the MCP Apps JS SDK to receive the tool result and display the image in a sandboxed iframe.

The HTML loads the ext-apps SDK from unpkg, so the resource declares csp=ResourceCSP(resource_domains=["https://unpkg.com"]) to allow the host to set the appropriate Content-Security-Policy.