Creating a Custom App in ChatGPT (Browser Only)

This guide explains how to create a custom app (MCP app) in ChatGPT, similar to how private content apps work in Claude.

Important

• This currently only works in the ChatGPT browser experience
• The app is not yet available in the desktop or mobile apps

Prerequisites

Before you start, make sure you have:

• Access to Paid ChatGPT in the browser
• An API key for your MCP server
• The MCP server URL:

https://mcp.cashmere.io?api_key=<API_KEY>

No additional authentication is required.

Step 1: Open Settings

1. Open ChatGPT in your browser
2. Click your profile icon in the bottom-left corner
3. Select Settings

📸 See screenshot: Settings highlighted in the ChatGPT menu

Step 2: Enable Developer Mode

1. In Settings, navigate to Apps
2. Click Advanced settings
3. Toggle Developer mode ON

Developer mode allows you to add unverified MCP apps.

Use at your own risk — memory is disabled for these apps.

📸 See screenshot: Developer mode toggle enabled

Step 3: Create a New App

1. While still in Apps → Advanced settings
2. Click Create app

📸 See screenshot: “Create app” button

Step 4: Configure the App

Fill out the app configuration form:

Required Fields

• Icon (optional)
  • Minimum size: 128 × 128 px
• Name
  • This is the name you’ll use to call the app in chat
  • Example:

@cashmere

• MCP Server URL

https://mcp.cashmere.io?api_key=<API_KEY>

Optional Fields

• Description
  • Brief explanation of what the app does

  • Example:

    Access and query licensed Cashmere content directly in ChatGPT

📸 See screenshot: New App modal with fields filled out

Step 5: Authentication Settings

1. Under Authentication, select:

No Auth

2. Confirm the risk warning acknowledging:
   • OpenAI has not reviewed the MCP server
   • The app may access or modify data

📸 See screenshot: “No Auth” selected and risk confirmation

If the server uses Cashmere authentication instead, ChatGPT sends you through a Cashmere sign-in and you pick the collections to connect. Publishers can turn on Skip collection selection on the server so it grants its own collections and the picker never appears. See section 4.2 of the Cashmere Link guide.

Step 6: Create the App

1. Click Create
2. The app will now appear in your Apps list

Step 7: Use the App in ChatGPT

Once created, the app is immediately available in chat.

To use it:

@<app-name>

Example:

@cashmere list available publications

ChatGPT will route requests to your MCP server automatically, similar to how Claude handles private content apps.

Notes & Limitations

• ✅ Works in ChatGPT browser
• ❌ Not supported in desktop app
• ❌ Not supported in mobile app
• Memory is disabled for developer-mode apps
• No additional login or OAuth flow required

Summary

You’ve now created a ChatGPT app that:

• Behaves similarly to a Claude private content app
• Is callable via @ in chat
• Connects directly to your MCP server using an API key
• Requires no authentication setup