Issues

Issues

• Support C# union return values in tools, prompts, and resources

  modelcontextprotocol/csharp-sdk#2015 · opened on Nov 10, 2026

• 2.4.0: tools/call results with annotated content blocks fail to serialize (InvalidOperationException in ContentBlock.Converter.CreateNestedOptions)

  modelcontextprotocol/csharp-sdk#2012 · opened on Nov 10, 2026
  1

• With UnmappedMemberHandling = Disallow, a tool call with an undeclared argument fails with an error that names nothing

  modelcontextprotocol/csharp-sdk#2011 · opened on Nov 9, 2026 · Future
  1

• Stdio client send can hang forever, or fail with a bare "Failed to send message.", when the server exits at once

  modelcontextprotocol/csharp-sdk#2005 · opened on Nov 8, 2026 · 2.x

• StreamServerTransport materializes each stdio line as a string, costing ~9× the frame size per large request, with no upper bound on message size

  modelcontextprotocol/csharp-sdk#2004 · opened on Nov 7, 2026
  2

• Define consistent strict and diagnostic validation for client list APIs

  modelcontextprotocol/csharp-sdk#1997 · opened on Nov 5, 2026 · Future

• Support caller-controlled aggregation budgets across client list APIs

  modelcontextprotocol/csharp-sdk#1996 · opened on Nov 5, 2026 · Future

• Highlight community projects

  modelcontextprotocol/csharp-sdk#1992 · opened on Nov 5, 2026 · Future

• Client hands progress notifications to IProgress out of order

  modelcontextprotocol/csharp-sdk#1991 · opened on Nov 3, 2026
  1

• Support Skills authorization without cross-package dependencies

  modelcontextprotocol/csharp-sdk#1990 · opened on Nov 3, 2026

• Client: option to return the MRTR InputRequiredResult instead of resolving it in-process

  modelcontextprotocol/csharp-sdk#1985 · opened on Nov 1, 2026 · 2.x

• Invalid UTF-8 in a request string returns 500 instead of 400 (Streamable HTTP)

  modelcontextprotocol/csharp-sdk#1984 · opened on Nov 1, 2026
  2

• Large tool results allocate ~20× the payload size while being serialized

  modelcontextprotocol/csharp-sdk#1971 · opened on Oct 28, 2026
  1

• Static resources whose URIs differ only in the fragment or user info collapse into one

  modelcontextprotocol/csharp-sdk#1970 · opened on Oct 28, 2026
  2

• POST /mcp with a missing or unparseable Content-Type returns HTTP 500 instead of a 4xx

  modelcontextprotocol/csharp-sdk#1966 · opened on Oct 27, 2026
  4

• Bugs in InMemoryMcpTaskStore lead to poor development / testing experience

  modelcontextprotocol/csharp-sdk#1963 · opened on Oct 26, 2026 · Future

• Route application-sent notifications/resources/updated to matching subscriptions/listen streams

  modelcontextprotocol/csharp-sdk#1930 · opened on Oct 14, 2026

• Session-level client extensions overwrite the per-request Tasks opt-in: CallToolAsTaskAsync never creates a task

  modelcontextprotocol/csharp-sdk#1920 · opened on Oct 12, 2026

• Streamable HTTP: a non-string params.name or params.uri throws in ValidateMcpHeaders and returns HTTP 500

  modelcontextprotocol/csharp-sdk#1919 · opened on Oct 12, 2026
  1

• Streamable HTTP returns -32600 instead of -32700 for malformed JSON

  modelcontextprotocol/csharp-sdk#1918 · opened on Oct 11, 2026

• UseStructuredContent: with the default serializer options, structuredContent omits a null property that outputSchema requires

  modelcontextprotocol/csharp-sdk#1915 · opened on Oct 10, 2026
  2

• Reserved URI-template expansion throws for supplementary Unicode characters

  modelcontextprotocol/csharp-sdk#1913 · opened on Oct 9, 2026
  1

• Track support for SEP-2127 MCP Server Cards

  modelcontextprotocol/csharp-sdk#1912 · opened on Oct 8, 2026

• Per-tool task support metadata in 2.x (replacement for Tool.Execution.TaskSupport)

  modelcontextprotocol/csharp-sdk#1911 · opened on Oct 6, 2026

• WithTools<T>() + MapMcp() keeps every host alive after disposal (AIFunctionFactory's static descriptor cache holds the tool's create options)

  modelcontextprotocol/csharp-sdk#1904 · opened on Oct 2, 2026
  1