Extension

Extension Support Matrix

Which MCP clients implement which official extensions

Source · Built from 40123d1 · 2026-09-29

This matrix shows which MCP clients support each official extension. Extensions are always opt-in: a client only uses an extension if both client and server declare support in the extensions field of their capabilities.

Extension overview

Extension	Identifier	Description
MCP Apps	`io.modelcontextprotocol/ui`	Interactive HTML interfaces rendered inline in the conversation
OAuth Client Credentials	`io.modelcontextprotocol/oauth-client-credentials`	Machine-to-machine auth without interactive user login
Enterprise-Managed Authorization	`io.modelcontextprotocol/enterprise-managed-authorization`	Centralized access control via enterprise IdP
Skills over MCP	`io.modelcontextprotocol/skills`	Discover skills and read their instructions and supporting files

Support matrix

Client	MCP Apps	Enterprise Auth	Skills
Claude (web)	✓
Claude Desktop	✓
VS Code GitHub Copilot	✓
Microsoft 365 Copilot	✓
Goose	✓
Postman	✓
MCPJam	✓
ChatGPT	✓		Partial
Cursor	✓
Archestra.AI	✓	✓
PostHog Code	✓
fast-agent			Partial
MCP Inspector			Partial

Adding extension support to your client

If you're building an MCP client and want to implement extension support:

Review the extension specification (e.g., in the ext-auth or ext-apps repository)
Declare support in the extensions field of the io.modelcontextprotocol/clientCapabilities your client sends in each request's _meta, and read the server's extensions from its server/discover response
Implement the extension's protocol requirements
Submit a pull request to update this matrix

See Extensions Overview for details on the capability negotiation mechanism.