ChatGPT MCP Integration: Custom Connector Setup Guide

To set up a ChatGPT MCP integration, turn on Developer mode in ChatGPT web, create an app, and paste in your MCPifex gateway URL with your API key at the end. Choose No Authentication, create the connection, and select the app in a conversation. Below are the steps, a first test, and the Responses API option for developers.

Add MCPifex in ChatGPT web

Your connection URL is the gateway address plus your key:

https://mcpifex.com/mcp/<YOUR_MCPX_KEY>

1. In the MCPifex portal, open your instance, enable the tools you need, run Test connection and generate an API key.
2. In ChatGPT web, open Settings → Security and login and turn on Developer mode.
3. Open ChatGPT Plugins, select the plus button and create a developer-mode app. Give it a name and description you'll recognize.
4. Enter https://mcpifex.com/mcp/<YOUR_MCPX_KEY>, replacing the placeholder with your full key.
5. Select No Authentication. Leave the OAuth fields empty.
6. Create the connection and look over the tools it finds. In a conversation, open the plus menu, choose Developer mode and select the app.

Treat this URL like a password. Keep it out of screenshots, prompts and shared docs. If it leaks, revoke the key in the portal and update the app with a new one. New calls stop within about a minute, and an open session is cut off on its next tool call.

OpenAI's connection guide has the current interface. Older screenshots showing Settings → Connectors → Create may be from an earlier release.

Why "No Authentication"?

OpenAI offers OAuth, No Authentication and Mixed Authentication. With No Authentication, ChatGPT runs no sign-in flow of its own. The gateway still checks the key inside the URL, so the endpoint isn't open to anyone without one.

Only the MCPifex key goes in that URL. Database passwords and Google credentials belong in the instance settings. The API keys and authentication page covers both ways to send a key.

What you need

As of September 2026, OpenAI documents web Developer mode for Pro, Plus, Business, Enterprise and Education accounts. A workspace admin can restrict it. If the option is missing, check the current developer-mode documentation.

You also need a hosted server to point at. The quickstart shows how to create an instance. PostgreSQL is a good first one because schema discovery and read-only queries are easy to check.

Test with a read-only request

First compare the app's tool list with the tools you enabled on the instance. Then ask ChatGPT for something bounded, like "List the schemas in my database." Expand the tool call and read the returned data. A general explanation of schemas doesn't prove the integration ran.

The portal's per-instance call log shows whether a request reached MCPifex. If Test connection passes but ChatGPT finds no tools, look at the app connection and the key. If a tool runs but returns an error, look at the source system's settings and permissions.

Keep write tools off unless you need them

ChatGPT Developer mode supports read and write tools. It asks for confirmation on writes by default, but you can remember an approval or denial for a tool within a conversation, so a prompt won't always appear. Check the input before you approve anything consequential.

MCPifex has its own layer. Write and destructive tools are off by default, and disabled tools are hidden and refused. Asking the model to avoid writes is no substitute for turning off tools you don't need.

Using the Responses API instead

If you're building an app, the Responses API has an MCP tool with fields such as server_label, server_url, allowed_tools and require_approval. An optional authorization field carries a bearer token. The MCP and Connectors reference covers the approval flow.

With MCPifex, set server_url to the base gateway URL and pass your API key as the bearer token. Keep the key in your app's secrets, and send it with each request, since OpenAI doesn't store that value. Start with a short allowed_tools list and explicit approvals.

If it doesn't work

• No Developer mode: check your account type and your workspace's app policy.
• 401 error: the key or URL is wrong, or the key was revoked. Generate a new key.
• Missing tools: compare with the instance's enabled tools, refresh the app's tool list, and check the app is selected in this conversation.
• Protocol error: MCPifex's gateway uses the handshake-based MCP transport. Clients on the current revision interoperate through the spec's backward-compatibility rules. Note the error and the client you used.

About MCPifex

MCPifex hosts MCP servers so you don't have to install them. Browse the marketplace, create an instance, and connect it to ChatGPT with one key. The free plan includes 3 instances.