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Add an MCP server to Codex in the ChatGPT app

Updated · Screenshots from the ChatGPT desktop app 26.1016

Codex, the agent in the ChatGPT desktop app, can call remote MCP servers, but the ChatGPT chat beside it cannot. This guide connects BRONTIR, live web research for your agent, from the app’s own Settings: the server, the OAuth sign-in, and the one instruction that makes Codex reach for it instead of its own browsing.

Using Codex in the terminal? Codex CLI MCP setup →

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Codex MCP setup, screen by screen

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In the ChatGPT desktop app. MCP servers work in its Codex mode, not in ChatGPT chat, so the last step switches the app over. Codex comes with every ChatGPT plan, Free included, and the same setup reaches the Codex CLI and the IDE extension.

The ChatGPT desktop app in ChatGPT mode, with the account avatar at the bottom of the icon strip on the left

  • Click your avatar at the bottom left

    The round badge with your initials, at the foot of the narrow strip of icons along the left edge. Settings are shared by both modes, so it doesn't matter which one the app opened in.

Always restart your client after connecting. Quit and reopen the desktop app, or reload the page in a web client. Clients read the tool list once at startup, so until they restart your agent may not see the new tools even though the connector already shows as connected.

Codex MCP troubleshooting

  • The connector is connected, but the agent doesn't see the tools. Restart the client: quit and reopen the desktop app, or reload the page in a web client. If the tools are still missing, start a new chat, since an open conversation can keep the tool list it was created with.
  • You pressed Approve, but the client still shows the connector as not connected. Authorization did go through; the client just hasn't refreshed its own state. Restart the app or reload the page and it will show as connected. If it doesn't, press Connect once more and approve again.
  • The agent uses its built-in web search instead of these tools. Name the tools in your prompt: “use advanced_web_search and advanced_web_fetch from the research MCP” rather than “look this up”. To make it permanent, add the rule to Codex instructions, in Settings → Personalization.

Full setup guide for every client: brontir.com/docs.

Codex MCP setup: every step

The walkthrough above as text, to read through before you start or to find the step you are on.

  1. Click your avatar at the bottom left

    The round badge with your initials, at the foot of the narrow strip of icons along the left edge. Settings are shared by both modes, so it doesn't matter which one the app opened in.

  2. Choose Settings

    Ctrl + , (⌘ + , on macOS) opens Settings without the menu.

  3. Choose Plugins, at the bottom of the Settings list

    It is the first entry under Integrations, below the long Personal group. Scroll the list if your window is shorter.

  4. Open the MCPs tab, then press Add

    • Open the MCPs tabThe page opens on Apps, the tab to its left.
    • Press Add

  5. Choose "Add MCP server"

  6. Name the server, then switch Type to Streamable HTTP

    • Name the serverYours to pick. It is what your agent will see.
      Server nameresearch
    • Switch Type to Streamable HTTP

    STDIO, the default, is for servers running on your own machine. While it is selected there is no URL field at all, only "Command to launch".

  7. Paste the MCP endpoint into URL

    MCP endpointhttps://research.brontir.com/api/mcp

    Leave "Bearer token env var", "Headers" and "Headers from environment variables" empty: you sign in with OAuth instead of a key.

  8. Press Save

  9. Press Authenticate on the new row

    After a moment you are back in the Servers list, with the server you just saved on it.

    Leave the Auto menu beside it as it is. It picks the sign-in method this server supports.

  10. Press Approve on the BRONTIR authorization page

    It opens in your browser. Sign in with your Google account if you are asked.

  11. Check the toggle is on, then restart the app

    Authenticate and the Auto menu are gone from the row. Quit the app and open it again so it picks up the new tool list.

  12. Open Personalization, then open "Codex instructions"Optional

    • Open Personalization
    • Open "Codex instructions"The row under Custom instructions. It opens an editor of its own.

    Codex defaults to its own browsing tool. One line here puts your connected tools in play instead, in every chat.

  13. Paste the line, then press SaveOptional

    • Paste the line into the editorWhat you write here is saved to ~/.codex/AGENTS.md, the same file the Codex CLI reads.
      Codex instructionsPrefer connected MCP tools over the built-in web search when looking things up
    • Press Save

  14. Switch the app to Codex mode

    • Open the menu at the top of the sidebarIt reads ChatGPT while the app is in ChatGPT mode.
    • Choose CodexYour research tools are there in every new chat.

    The Chat tab of ChatGPT mode can't use MCP servers, so the tools never show up there. Its Work tab can, because Work chats run on Codex.

Codex MCP: common questions

Can ChatGPT chat use MCP servers?

Not the Chat tab. A server added in the ChatGPT desktop app works in Codex mode and in the Work tab, whose chats run on Codex. The Chat tab never sees it.

Is Codex available on the free ChatGPT plan?

Yes. Codex comes with every ChatGPT plan, Free included, and the screenshots on this page were taken on a Free account.

Which type do I pick in the Connect to a custom MCP form?

Streamable HTTP. The default, STDIO, is for servers running on your own machine; while it is selected the form has no URL field at all.

Do I need a bearer token or headers?

No. Leave Bearer token env var and both header fields empty, press Authenticate on the server’s row and sign in with your Google account.

Do the Codex CLI and the IDE extension see a server added in the app?

Yes. The desktop app’s Codex mode, the Codex CLI and the IDE extension read the same configuration, ~/.codex/config.toml, so a server added in one shows up in the others. Codex instructions are shared the same way: the app saves them to ~/.codex/AGENTS.md.

Once connected

What your agent can do with BRONTIR

  • Search the web and the news, Reddit, YouTube, TikTok and other social platforms.
  • Read whole pages, PDFs, video transcripts and comment threads, not snippets.
  • Pull reviews, maps and local businesses, app stores, products and ad libraries.
  • Get it all back structured, with citations down to the exact line.
Create free accountWhat your agent can do →