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 open-sourced mcp-extensions, an Apache 2.0 SDK for building ChatGPT-native MCP plugins.
- Adds sidebar, thread, and file-extension entrypoints so plugins can live outside the chat bubble.
- File handlers support reading, subscribing, and writing with ETag-based conflict detection.
- Composer at-mentions let users search and reference individual plugin resources inline.
- Structured settings render as native ChatGPT controls from a declarative JSON schema.
- TypeScript and Python SDKs ship alongside a full spec and demo Bits & Bolts plugin.
OpenAI brings MCP apps into ChatGPT’s interface
OpenAI has published the mcp-extensions repository, 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. 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. |
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