Issues

• UriTemplate.match() cannot read back prefix{.ext} when ext holds a dot, though nothing else can claim it

  bugv2
  modelcontextprotocol/python-sdk#3693 · Filter by author chrikrah opened on Oct 12, 2026

• Tool handlers returning UserList lose native content blocks despite Sequence return annotation

  bugv1v2
  modelcontextprotocol/python-sdk#3692 · Filter by author OHHZZ opened on Oct 12, 2026
  1

• Streamable HTTP: Content-Type handling is order dependent and accepts invalid values

  bugv1v2
  modelcontextprotocol/python-sdk#3691 · Filter by author aabidk20 opened on Oct 12, 2026
  1

• Skills: URI traversal validation skips percent-encoded dot-segments

  bugv2
  modelcontextprotocol/python-sdk#3685 · Filter by author chauvuusvn opened on Oct 12, 2026

• Add a filesystem backed provider for the Skills extension

  enhancement
  modelcontextprotocol/python-sdk#3683 · Filter by author vijaydeepsinha opened on Oct 11, 2026
  1

• [v1.x] Server revalidates every tools/call with one-shot jsonschema.validate(), re-checking the schema each time

  bugv1
  modelcontextprotocol/python-sdk#3676 · Filter by author mechnotech opened on Oct 11, 2026
  1

• stdio server never exits on stdin EOF while the client leaves stdout unread

  bugv1v2
  modelcontextprotocol/python-sdk#3674 · Filter by author superbiche opened on Oct 10, 2026
  1

• Type annotation gaps and unhandled FileNotFoundError in src/mcp/cli/cli.py

  enhancement
  modelcontextprotocol/python-sdk#3673 · Filter by author avk-dwvd opened on Oct 10, 2026
  4

• DPoP sender-constrained tokens not implemented in OAuth client (spec mandates it)

  enhancement
  modelcontextprotocol/python-sdk#3671 · Filter by author eaakun opened on Oct 10, 2026
  2

• Streamable HTTP server rejects a mixed-case Content-Type with 415

  bugv1v2
  modelcontextprotocol/python-sdk#3670 · Filter by author v0ropaev opened on Oct 10, 2026
  4

• MCPServer answers an unknown prompt name or a missing required argument with code 0 / -32603; the spec uses -32602

  bugv1v2
  modelcontextprotocol/python-sdk#3669 · Filter by author ANcpLua opened on Oct 10, 2026
  4

• @app.tool() raises NameError for parameter/return types defined later in the module on Python 3.14+ (PEP 649/749 deferred annotations)

  bugv1v2
  modelcontextprotocol/python-sdk#3668 · Filter by author ao3575911 opened on Oct 9, 2026
  3

• [v2] Docs: Arabic translation of the SDK documentation (offering to contribute and maintain)

  enhancementv2
  modelcontextprotocol/python-sdk#3665 · Filter by author m0hamed-ux opened on Oct 9, 2026

• Bug in the MCP Apps documentation.

  documentationv2
  modelcontextprotocol/python-sdk#3662 · Filter by author pdelboca opened on Oct 9, 2026

• SSE transport: invalid Host/Origin header on /sse crashes entire server process, not just that request

  bugv1v2
  modelcontextprotocol/python-sdk#3661 · Filter by author Stonica opened on Oct 9, 2026
  2

• MCPServer answers an unknown tool with an isError result; the spec (and the TS SDK) use JSON-RPC -32602

  bugv1v2
  modelcontextprotocol/python-sdk#3659 · Filter by author ANcpLua opened on Oct 8, 2026
  5

• Audio(data=b"") raises "Either path or data can be provided", while Image(data=b"") works

  bugv1v2
  modelcontextprotocol/python-sdk#3656 · Filter by author xThreeh opened on Oct 8, 2026
  2

• Simple chatbot: consider removing cleanup lock from sequential lifecycle

  enhancement
  modelcontextprotocol/python-sdk#3655 · Filter by author JEFFTIMES opened on Oct 7, 2026

• CORSMiddleware on /register and /token forwards any non-preflight OPTIONS request straight to the body-reading handler

  bugv1v2
  modelcontextprotocol/python-sdk#3652 · Filter by author JordanAfolabiLaw opened on Oct 7, 2026
  3

• MCPServer completion handler returning more than 100 values fails on 2026-07-28 sessions and violates the 100-item limit on 2025-11-25 sessions

  bugspec-2026-07-28v2
  modelcontextprotocol/python-sdk#3649 · Filter by author KardeniaPoyu opened on Oct 6, 2026
  3

• Prompt handlers returning UserList are rendered as one text message

  bugv1v2
  modelcontextprotocol/python-sdk#3643 · Filter by author pasmud opened on Oct 5, 2026
  1

• ServerCapabilities drops unknown keys, so a server can't advertise events for ChatGPT's MCP Events

  bugspec-2026-07-28v2
  modelcontextprotocol/python-sdk#3640 · Filter by author s1980amber-commits opened on Oct 3, 2026
  4

• Streamable HTTP client hangs on a null-id JSON-RPC error in a 200 JSON response

  bugv1v2
  modelcontextprotocol/python-sdk#3639 · Filter by author hyeonsang010716 opened on Oct 3, 2026
  2

• Streamable HTTP notification triggers duplicate response after HTTP 202

  bugv1v2
  modelcontextprotocol/python-sdk#3631 · Filter by author lecton-apptio opened on Oct 2, 2026
  3

• SSE: a POST blocks forever (and SIGTERM hangs) when the server lifespan raises after an await

  bugv1v2
  modelcontextprotocol/python-sdk#3616 · Filter by author khuisman opened on Oct 2, 2026
  2