How to Connect ChatGPT to an MCP Server

ChatGPT supports MCP (Model Context Protocol) servers. That means you can connect it to your notes, calendar, database, or any other service that speaks MCP.

What you need

A ChatGPT account (Plus, Pro, Business, Enterprise, or Education for developer mode)
An MCP server URL from the service you want to connect (for example, https://hjarni.com/mcp)

Developer mode and custom MCP apps are currently in beta and available on the web.

Connecting via ChatGPT

ChatGPT supports remote MCP servers through developer mode. You create an "app" linked to your MCP server, then turn it on when you need it.

Step 1: Enable developer mode

Open ChatGPT and go to Settings > Apps
Scroll to Advanced settings
Toggle Developer mode on

Step 2: Create an app from your MCP server

In the developer mode settings, click Create app
Enter your MCP server URL (e.g. https://hjarni.com/mcp)
Complete the OAuth authentication flow if the server requires it
Review the available tools and toggle on the ones you want

Step 3: Use the app in a conversation

Start a new conversation
Click the + (plus) menu and choose Developer mode
Select the apps you want ChatGPT to use
ChatGPT can now call the server's tools. Write actions require your approval before they run.

What ChatGPT can do with MCP

Once connected, ChatGPT can use whatever tools that server offers. For example, when connected to a knowledge base like Hjarni, ChatGPT can:

Find relevant notes by keyword or topic

Read

Pull in the full content of any note for context

Create

Save new notes directly from a conversation

Organize

Tag notes, move them between folders, add links

Follow instructions

Read your custom AI instructions and apply them to every response

The specific capabilities depend on the MCP server. Each server exposes its own set of tools.

Verifying the connection

Start a new conversation and ask ChatGPT to use one of the server's tools. For example, if you connected Hjarni:

"What notes do I have in Hjarni?"

ChatGPT should respond with your notes or confirm it has access. If you see tool calls in the response, the connection is working.

Troubleshooting

ChatGPT says it cannot connect

Verify the MCP server URL is entered correctly and that you completed the OAuth flow. Try removing the app and adding it again.

ChatGPT does not see your data

Make sure you selected Developer mode from the + menu and enabled the app for the current conversation. Also check that the right tools are toggled on in the app settings.

Developer mode does not appear

Developer mode is available in beta on Plus, Pro, Business, Enterprise, and Education plans (web only). Check your plan in ChatGPT settings.

Try it with Hjarni

Hjarni is a knowledge base with a built-in MCP server. Connect it to ChatGPT and stop re-explaining yourself. Your AI reads your notes directly.

The MCP server URL is https://hjarni.com/mcp. Two minutes to set up.

Connect your notes

Write once. You both remember.

Free to start. No credit card required.

Get started, it's free

Works with Claude and ChatGPT today. Gemini coming soon.