Building a ChatGPT MCP for the new Developer Mode – Complete Tutorial

Comprehensive Guide to Building a ChatGPT MCP Implementation with New Developer Mode Support

Exploring the latest advancements in ChatGPT’s capabilities opens up exciting opportunities for developers. Recently, OpenAI introduced official support for MCP (Model Control Protocol) within ChatGPT’s Developer Mode, enabling a new level of platform extensibility. This article offers a detailed overview and step-by-step tutorial to help you build your own MCP server and integrate it seamlessly with ChatGPT.

Introducing MCP Support in ChatGPT Developer Mode

Last week marked a significant milestone in AI development: the official announcement of ChatGPT’s Developer Mode now supporting MCP Server Tools. This enhancement enables ChatGPT to function as a bona fide MCP client, establishing direct communication with custom servers through Streamable HTTP (and the legacy HTTP-over-SSE transport).

Prior to this update, MCP functionalities within ChatGPT were limited to rudimentary fetches and searches, with third-party integrations primarily relying on the somewhat cumbersome plugin system introduced over a year ago. The new Developer Mode consolidates and streamlines this process, allowing developers to:

• Create custom tools
• Enable ChatGPT to discover these tools dynamically
• Request user approval within the chat
• Invoke external services directly during conversations

This robust shift aligns ChatGPT’s native environment with the MCP capabilities previously accessible only via the Responses API and the Agents SDK, now with native support within the ChatGPT interface itself.

Practical Applications: Building an MCP Server for Your Ecosystem

To demonstrate the potential of this feature, I developed a lightweight, Streamable HTTP-based implementation of my Flow Nexus system—a versatile platform capable of deploying sandboxes, managing neural network training, and orchestrating complex workflows. This prototype illustrates how developers can leverage MCP for real-world integration scenarios.

The tutorial below provides comprehensive, step-by-step instructions to help you:

• Set up your own MCP server
• Implement communication protocols over SSE
• Connect your server with ChatGPT’s Developer Mode
• Test and refine your integrations in real-time

Getting Started: Resources and Live Demos

• Explore the live MCP Flow Nexus prototype at https://mcp-flow-nexus.ruv.io, showcasing a Streamable HTTP implementation in action.
• Read the full tutorial and detailed walkthrough on LinkedIn: [Building a ChatGPT MCP for Developer Mode — Complete Tutorial](https://www.linkedin.com/pulse/build