How to Add an MCP Server to ChatGPT With Developer Mode

By Eric Parker, founder of TrueCal. Published October 1, 2026. Sources checked October 1, 2026.

Written with AI assistance from the cited studies. Every claim was checked against its source. Editorial policy.

Key takeaways

Developer mode lets ChatGPT Plus, Pro, Business, Enterprise and Edu accounts add a remote MCP server, on the web.¹
As of October 2026, turn it on in Settings > Security and login > Developer mode, then add your server from ChatGPT Plugins with the plus button.
ChatGPT connects to MCP servers over SSE or streaming HTTP, with OAuth, no authentication, or a mix of the two.¹
Write actions ask for your confirmation by default, and OpenAI calls developer mode powerful but dangerous, so add only servers you trust.¹

Who can add an MCP server to ChatGPT?

Developer mode is for ChatGPT Plus, Pro, Business, Enterprise and Edu accounts, on the web. It lets you add a remote MCP server as a developer mode app and use its tools in a chat.¹

OpenAI's help center article on developer mode still shows an older menu path and says Pro gets read and fetch tools only. When the two disagree, the steps below follow the developer guide.²

How to turn on developer mode and add a server

OpenAI's developer guide puts the switch under Settings, then Security and login, and has you create the app from ChatGPT Plugins with the plus button. In a chat, you open the plus menu, choose Developer mode, and pick your app.¹

As of October 2026, open ChatGPT on the web and go to Settings > Security and login, then turn on Developer mode.
Open ChatGPT Plugins and select the plus button to create a developer mode app.
Enter a name, a description and your server's MCP URL, and choose the sign-in type your server uses.
If the server uses OAuth, finish its sign-in.
In a chat, open the plus menu, choose Developer mode, and pick your app. Name the app and tool in your request so ChatGPT calls the right one.

What sign-in options does ChatGPT support?

Developer mode supports OAuth, no authentication, or mixed authentication, which pairs OAuth with a no-auth fallback. It also supports Client ID Metadata Documents and Dynamic Client Registration.¹

ChatGPT connects to remote MCP servers over SSE or streaming HTTP, so the server has to be reachable over the web.¹

Read tools versus write tools

ChatGPT treats a tool as read-only only when the server marks it with the readOnlyHint annotation. Every other tool counts as a write action.¹

Write actions ask for your confirmation by default, so check the tool's inputs before you approve. You can have ChatGPT remember your choice for the rest of a conversation, and a new conversation asks again.¹

OpenAI calls developer mode powerful but dangerous. Its guide warns about prompt injection, model mistakes on write actions that can change or delete data, and malicious servers that try to steal information.¹

Add only servers you trust, and turn off tools you don't need in the app's settings.

Adding TrueCal as a custom MCP server

TrueCal is not in the ChatGPT plugin directory yet. On ChatGPT Plus or a higher plan, you can add it yourself on the web with developer mode.⁵

Once connected, you can ask TrueCal to log a meal from text, log water or weight, show today's diary or your weekly trend, find a past meal, and save or apply meal templates. Meal logging in ChatGPT is text only, so use the TrueCal app for photos and barcodes.⁵

Name the app TrueCal and give it a short description, such as food log.
For the MCP URL, copy the address shown in the TrueCal in ChatGPT guide.
Sign in with the Google account that uses the same email as your TrueCal login, or create a TrueCal account from ChatGPT.

Troubleshooting

Tools not showing. Check that developer mode is on and that you picked the app from the plus menu in this chat, then refresh the app in its settings to pull updated tools.
Sign-in fails or loops back. Add the app again and finish the sign-in in the same browser window.
TrueCal says no account exists for your Google email. Sign in with the Google account that uses the same email as your TrueCal login, or create a TrueCal account from ChatGPT.

How this differs from installing a published plugin

A published plugin comes from the directory, and you add it from Settings, then Plugins, then Install plugin, then Connect. A developer mode app is one you add yourself by URL, and it sits under Drafts in app settings.³¹

OpenAI's troubleshooting page says Free and Go users can browse the directory, but plugin extensions aren't available on those plans. We haven't confirmed how that applies to each plugin. Developer mode needs Plus or a higher plan either way.⁴¹

If you use Claude, the TrueCal CLI and connector guide in the related links covers the Claude setup.

Worked example

Here's TrueCal as the example, as of October 2026. Turn on developer mode under Settings, then Security and login. In ChatGPT Plugins, select the plus button, name the app TrueCal, and enter TrueCal's MCP address. Sign in with the Google account that uses the same email as your TrueCal login. In a chat, choose Developer mode from the plus menu and type, TrueCal, log two eggs and a slice of toast for breakfast. TrueCal saves the meal to the same food log you see on iPhone, Android and the web.¹⁵

A closer look

OpenAI's developer mode guide lists ChatGPT Plus alongside Pro, Business, Enterprise and Edu, on the web, and puts the switch under Settings, then Security and login. New developer mode apps sit under Drafts in app settings, where you can turn single tools on or off and refresh the app to pull updated tools from the server.¹

Questions and answers

Can I use developer mode in the ChatGPT phone app?

OpenAI's guide lists developer mode for accounts on the web, so set it up in a browser.¹

Is ChatGPT developer mode a jailbreak?

No. In OpenAI's docs, developer mode is a setting that lets you add MCP servers as apps and use their tools in a chat.¹

Can I connect a local MCP server?

OpenAI's guide covers remote MCP servers over SSE or streaming HTTP, so the server needs a web address ChatGPT can reach.¹

Is TrueCal in the ChatGPT plugin directory?