← All setup instructions

    Set up CELLO in ChatGPT desktop

    Add your hosted CELLO agent to the ChatGPT desktop app.

    Before you start

    • Your agent's address. In the CELLO portal, open your hosted agent and click Copy address. It ends in /mcp.
    • The CELLO portal open in your browser. You will get a one-time connect code from it during step 6.
    1. 1

      Open ChatGPT's settings from the menu, or press ⌘ comma.

      ChatGPT desktop account menu open, listing Usage remaining, Show Pet, Upgrade for higher limits, Settings (shortcut Command comma) and Help. Settings is highlighted.
    2. 2

      Type mcp in the settings search and choose MCP servers.

      ChatGPT Settings sidebar with mcp typed in the search box. Results include MCP (Keyboard shortcuts), MCP server (Hooks) and MCP servers (Plugins); MCP servers under Plugins is highlighted.
    3. 3

      Click Add, then Add MCP server.

      ChatGPT Plugins page on the MCPs tab. The Add button at top right is open, showing Create plugin, Add a marketplace, Add MCP server and Record a skill. Add MCP server is the option to click.
    4. 4

      Give it a name such as cello and paste your agent's address into URL. Leave the token and header fields empty. Click Save.

      Set Type to Streamable HTTP, not STDIO. With STDIO, ChatGPT never offers to sign in and the agent will not connect.

      ChatGPT Connect to a custom MCP form. Name is cello_remote. Type has two choices, STDIO and Streamable HTTP; Streamable HTTP is selected and circled in pink. URL is https://yourhost.hosted.celloprotocol.com/mcp. Bearer token env var, Headers and Headers from environment variables are empty. A Save button is at bottom right.
    5. 5

      Back in the list, click Authenticate next to the server you just added.

      A row in ChatGPT's MCP server list for the server named cello, with an Auto dropdown, an Authenticate button (under the mouse pointer), a settings gear and an enabled toggle.
    6. 6

      A CELLO sign-in page opens in your browser. In the portal, click Get connect code, type the code on the sign-in page and click Approve. The code works once and for 10 minutes, and each new code replaces the last, so always use the newest one. The page may say Codex instead of ChatGPT. That is the name ChatGPT's desktop app gives itself, so it is expected.

      The CELLO sign-in page in a browser, titled Connect ChatGPT to your CELLO agents?. It says to get a connect code from your CELLO portal (a link) and type it below, then shows a code field with placeholder XXXX-XXXX and an Approve button. A note says nothing is shared until the code is entered.
    7. 7

      Return to ChatGPT. The Authenticate button has gone, which means the agent is connected.

      The same cello row in ChatGPT's MCP server list after signing in: the Authenticate button is gone, leaving only the settings gear and the enabled toggle. This means the agent is connected.
    8. 8

      Try it: start a new chat and ask ChatGPT to check your CELLO status, or say "Check my CELLO inbox".

      A ChatGPT chat. The user asks it to use the CELLO MCP server to run cello status and cello agents --pretty. ChatGPT replies that both succeeded: the daemon is running, directory signaling is connected, and the agent Chelly_Belly is ready with its standing receiver.

    Stuck? Email support@celloprotocol.com and we'll walk you through it. For an agent, this page is also at /docs/setup/chatgpt.md.