Can I build MCP Apps with the C# SDK?
I want to build an MCP App — the web-UI extension for MCP servers — using the modelcontextprotocol/csharp-sdk for .NET. Is this scenario supported yet, and is there sample code or a working example to follow? I'm looking at the thread that tracked the MCP Apps proof of concept for this SDK.
Originally asked on GitHub: https://github.com/modelcontextprotocol/csharp-sdk/issues/1182
4 answers
MCP Apps work with the C# SDK today. The proof-of-concept issue was closed on 2026-04-13, with a maintainer stating that MCP Apps work now and that remaining work is convenience features tracked in separate issues. An earlier contributor comment (2026-02-19) said the PoC had validated that nothing further is required for GA.
Resources from the thread:
- A maintainer shared a sample implementation on a branch (compare link (opens external site)) that uses global message filters such as
AddIncomingMessageFilter, with plans to merge it as a PR and adjust theMessageFilterAPI to separate message filters from request filters. The thread never confirms whether that PR landed. - A community member posted a working MCP Apps example in the microsoft/DataFactory.MCP repo under
DataFactory.MCP.Core/Resources/McpApps.
Caveats: one commenter asked whether the
AddIncomingMessageFilterfilters are necessary or whether they belong in the resource scripts handling host-to-app communication rather than applied server-side; the thread contains no answer. Another commenter asked whether the sample PR was merged and got no reply. A separate issue (#1431 (opens external site)) tracks the support the SDK should add for MCP Apps.General advice: this area is still settling, so pin the SDK version you test against and check issue #1431 before relying on the current API shape.
Did this work for you?- A maintainer shared a sample implementation on a branch (compare link (opens external site)) that uses global message filters such as
What @halter73 tried on GitHub (Outcome unclear)
A maintainer shared a sample MCP App implementation on a branch (compare link above) using AddIncomingMessageFilter, planning to merge it as a PR and adjust the MessageFilter API. The thread never confirms whether the PR was merged.
Did this work for you?What @EbramTawfik tried on GitHub (Worked)
A community member shared their working MCP Apps implementation in the microsoft/DataFactory.MCP repo under DataFactory.MCP.Core/Resources/McpApps.
Did this work for you?What @ShrayRastogi tried on GitHub (Outcome unclear)
A commenter asked whether AddIncomingMessageFilter filters are required and whether they should live in resource scripts for host-to-app communication rather than server-side. The thread does not answer this.
Did this work for you?
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