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MCP / API

Connect your agent

Add the OnlyChat MCP server to Claude, ChatGPT, Codex or Cursor: paste the server URL and send your API key as a Bearer token in the Authorization header. The steps per assistant and the capital-B gotcha.

Updated September 28, 20263 min read
Ask an AI about this page:Open in ChatGPT Open in Claude

Every assistant needs the same two things: the server URL and your API key sent as a Bearer token in the Authorization header. Create the key first on the API Keys page.

WhatValue
Server URLhttps://mcp.only-chat.ai/mcp
HeaderAuthorization: Bearer oc_live_your_key

The account page has a Copy URL button and an Open the documentation link that always shows the exact, up-to-date steps for each client.

app.only-chat.ai
The Connect your agent section with the server URL, Copy URL and Open the documentation

Claude

In Claude (claude.ai or the desktop app), the MCP is added as a custom connector.

  1. Open Settings, then Connectors, and click Add, then Add custom connector.
  2. Give it a name (for example OnlyChat) and paste the MCP server URL https://mcp.only-chat.ai/mcp, then Continue.
  3. On the next screen, under Authentication, choose No connection (the option for servers that use an API key instead of OAuth). Claude pre-selects Sign in now with a Detected badge: ignore it and switch to No connection, otherwise the connector will not work. Then under Request headers, click Add a header: name Authorization, value Bearer oc_live_your_key (capital B). Save.
  4. Open a new chat, enable the OnlyChat connector from the tools menu. Claude lists the OnlyChat tools and asks before each action.
claude.ai
Claude Settings, Connectors page, with the Add button and the OnlyChat custom connector in the list
claude.ai
The Add custom connector dialog with the Name and MCP server URL fields
claude.ai
The connector settings in Claude: Authentication set to No connection, and the Request headers section with the Add a header button

ChatGPT

In ChatGPT, the MCP is added as a plugin.

  1. Open Settings, then Plugins ("Manage your plugins, connected accounts, and permissions"), and add a new plugin: the New Plugin form opens.
  2. Fill in a name (for example OnlyChat). Under Connection, keep Server URL and paste https://mcp.only-chat.ai/mcp. Under Authentication, choose the API key option and enter Bearer oc_live_your_key (capital B).
  3. Tick I understand and want to continue, then Create.
  4. Set the permission. Every plugin has a permission level, and the default Allow low-risk tools only lets ChatGPT use the read tools. To let it create or change scripts, folders and media, open the plugin's permission and choose Allow all tools.
  5. In a chat, enable the OnlyChat plugin from the tools menu.

If you do not see Plugins in your settings, your ChatGPT plan does not include custom plugins: use Claude, Codex or Cursor instead.

chatgpt.com
ChatGPT Settings, Plugins page, with the default permission and the OnlyChat plugin in the list
chatgpt.com
The New Plugin form with Name, Connection Server URL, Authentication, the risk checkbox and Create

Codex and Cursor

For a coding agent, add the server to its MCP configuration file (Codex CLI config, or Cursor's mcp.json) with the URL and the same Authorization: Bearer header. Both then load the OnlyChat tools and can read and act from your terminal or editor.

The one gotcha

Write Bearer with a capital B in the header. bearer oc_live_... in lowercase is rejected with a 401. If your agent cannot connect, check that first, then that the key is still Active on the API Keys page.