Lily Ma presents a comprehensive developer guide for building and hosting ChatGPT apps on Azure Functions, covering architecture, integration, and deployment tips.

Host ChatGPT Apps on Azure Functions: Developer Guide

This guide explains how developers can build, host, and test ChatGPT apps using Azure Functions—a scalable, cloud-based serverless platform from Microsoft.

Overview of ChatGPT Apps

OpenAI’s ChatGPT apps enable users to interact with conversational bots that take actions, fetch data, and present custom UI elements directly in chat. For developers, these apps can reach millions of users instantly, without needing custom frontends.

Key Benefits

Native Integration with ChatGPT: Users launch apps via mentions or receive contextual app suggestions.
Contextual Actions: Apps do more than chat—they can trigger data fetches, execute tasks, and present custom UI.
Massive Distribution: Apps submitted to the ChatGPT Directory get instant visibility to ChatGPT’s large user base.

Architecture: MCP Servers as the Foundation

ChatGPT apps operate as remote MCP (Message Control Protocol) servers, exposing tools that:

Specify interactive UI elements via metadata.
Return results rendered in the chat as iFrames, supporting dynamic actions (buttons, maps, etc).

Example: Weather App Workflow

Users chat with @WeatherApp and request weather info.
ChatGPT calls the MCP server tool (get_current_weather) via streamable HTTP transport.
The server returns both readable text and machine data for UI rendering.
The specified output template embeds results in a customizable widget.

Hosting MCP Servers using Azure Functions

Azure Functions offer:

Scalable, burst-handling infrastructure (Flex Consumption plan)
Built-in authentication and authorization for secure hosting
Serverless billing (pay-per-use)

This makes Azure Functions ideal for hosting MCP servers powering ChatGPT apps.

Prerequisites

To follow the deployment steps, ensure you have:

An Azure subscription
Azure Developer CLI
ChatGPT Plus subscription (for developer mode testing)

Deploying MCP Server to Azure Functions

Clone the MCP server repository:

git clone https://github.com/Azure-Samples/chatgpt-app-azure-function-mcp

Authenticate with Azure:
```
azd auth login
```
Deploy the application:
```
azd up
```
- Enter environment name, select subscription, choose location
- After deployment, copy your app’s URL: https://<your-app>.azurewebsites.net

Code Walkthrough (Python FastMCP Example)

Key components in main.py:

get_weather_widget: UI resource for rendering weather data in ChatGPT
get_current_weather: Tool fetching weather using Open-Meteo API
Returns both content and structured data for widget
Metadata outputTemplate links UI with data

@resource("ui://widget/current-weather.html", mime_type="text/html+skybridge")
def get_weather_widget() -> str:
    """Interactive HTML widget to display current weather data in ChatGPT."""
    # ...code...

@mcp.tool(
    annotations={"title": "Get Current Weather", "readOnlyHint": True, "openWorldHint": True},
    meta={
        "openai/outputTemplate": "ui://widget/current-weather.html",
        "openai/toolInvocation/invoking": "Fetching weather data",
        "openai/toolInvocation/invoked": "Weather data retrieved"
    }
)
def get_current_weather(latitude: float, longitude: float) -> ToolResult:
    # ...fetch weather...
    return ToolResult(content=content_text, structured_content=data)

On ChatGPT invocation, the tool returns data for the widget, which is then rendered in an iFrame in the chat.

Testing in ChatGPT Developer Mode

Enable Developer mode in ChatGPT (Settings → Connectors → Advanced)
Add a new source: click + → More → Add sources
Fill out the form: Name (WeatherApp), MCP Server URL (https://<your-app>.azurewebsites.net/mcp), select No Auth
After setup, invoke the app by mentioning @WeatherApp in a chat (e.g., “@WeatherApp what’s the temperature in NYC today?”)

Submit Your App to ChatGPT App Directory

Review submission guidelines
Submit the app for public listing: App Directory

What’s Next

This post covered app hosting and integration. The next post will explain authentication and authorization for Azure-hosted MCP servers. Azure Functions MCP extension support for MCP Resources is coming soon.

Final Thoughts

ChatGPT apps bring rich interactivity and distribution to developers through the ChatGPT client. Hosting with Azure Functions provides a reliable, scalable backend for these new app experiences.

Resources and Further Reading

This post appeared first on “Microsoft Tech Community”. Read the entire article here