---
title: "OpenAI Opens MCP Extensions So Developers Can Build Apps Inside ChatGPT"
subtitle: "OpenAI released mcp-extensions, an open-source SDK that lets Model Context Protocol plugins render as native ChatGPT surfaces like sidebar apps, file viewers, and composer mentions."
url: "https://alphasignal.ai/news/openai-opens-mcp-extensions-so-developers-can-build-apps-inside-chatgpt"
author: "AlphaSignal Newsroom"
author_url: "https://alphasignal.ai/editorial-team"
company: "OpenAI"
company_url: "https://alphasignal.ai/company/openai"
published: "2026-09-30T23:18:08.000Z"
updated: "2026-10-02T12:23:45.194Z"
type: "Repo"
topics:
  - "Agents"
  - "Api"
subtopics:
  - "Mcp"
  - "Tool Use"
  - "Agent Frameworks"
upvotes: 253
source_url: "https://github.com/openai/mcp-extensions"
comments: 0
truncated: true
---

# OpenAI Opens MCP Extensions So Developers Can Build Apps Inside ChatGPT

> OpenAI released mcp-extensions, an open-source SDK that lets Model Context Protocol plugins render as native ChatGPT surfaces like sidebar apps, file viewers, and composer mentions.

# OpenAI brings MCP apps into ChatGPT’s interface

OpenAI has published the [mcp-extensions repository](https://github.com/openai/mcp-extensions), an Apache 2.0 toolkit for integrating Model Context Protocol apps with ChatGPT’s interface. It adds hooks for sidebar apps, thread tabs, custom file viewers, composer mentions, structured settings, and richer forms.

Baseline MCP lets clients discover tools, read resources, and exchange context with servers. Host-specific navigation, file handling, and native settings sit outside that specification. OpenAI defines those capabilities through additional metadata and methods documented in the [extension spec](https://github.com/openai/mcp-extensions/blob/main/docs/spec.md). Clients must implement the extensions to render the corresponding interface.

## Four routes into ChatGPT

The included Bits & Bolts CAD demo exercises four entrypoint types, each placing an MCP app in a different part of ChatGPT:

| Entrypoint              | What it provides                                                                                |
| ----------------------- | ----------------------------------------------------------------------------------------------- |
| **Global**              | A persistent sidebar item that opens a full-screen app with its own composer and thread layout. |
| **Thread**              | A content tab attached to a conversation, with a separate app instance for each thread.         |
| **File extension**      | A custom viewer for advertised file types such as .ipynb or .stl.                               |
| **Composer at-mention** | A typeahead search that lets users mention individual resources exposed by the MCP server.      |

_Preview only. Full text requires an AlphaSignal Pro account._

## Sources

- [openai/mcp-extensions on GitHub](https://github.com/openai/mcp-extensions)
- [OpenAI MCP Extensions Specification](https://github.com/openai/mcp-extensions/blob/main/docs/spec.md)
- [TypeScript SDK README](https://github.com/openai/mcp-extensions/blob/main/typescript/README.md)
- [Python SDK README](https://github.com/openai/mcp-extensions/blob/main/python/README.md)