---
title: "ChatGPT | Crossmart Docs"
description: "Add Crossmart to ChatGPT as a custom MCP server in developer mode and sign in with OAuth."
url: "https://docs.crossmart.io/agents/chatgpt/"
---

# ChatGPT

Checked on 2026-11-06 against [developers.openai.com: connect to ChatGPT](https://developers.openai.com/plugins/deploy/connect-chatgpt) and [build an MCP server](https://developers.openai.com/plugins/build/mcp-server). ChatGPT connects custom MCP servers with OAuth or with no authentication, not with an API key header, so it signs in to Crossmart with OAuth.

## Sign in with OAuth

Custom MCP servers are added in developer mode, on plans that allow it (full read and write is for Business and Enterprise/Edu workspaces; check [OpenAI’s help article](https://help.openai.com/en/articles/12584461) for your plan):

1. Open [chatgpt.com/plugins](https://chatgpt.com/plugins) and click **+**.
2. Choose **Add custom MCP server**.
3. Name: `Crossmart`. URL: `https://mcp.crossmart.io/mcp`.
4. Authentication: **OAuth**. Sign in to Crossmart, pick a workspace and approve the access.
5. **Create as a plugin**.

Don’t choose “No authentication”: the Crossmart server refuses requests without a key or token.

## Without OAuth

Use an agent that sends headers, such as [Codex CLI](https://docs.crossmart.io/agents/codex/) from OpenAI, or call the [REST API](https://docs.crossmart.io/developers/) from your own code.

## Skills

ChatGPT has no documented `SKILL.md` support. The tool descriptions on the Crossmart server carry the essential guidance (listing states, next steps) on their own.