Issues

• stdio_client with strict decoding withholds fatal read errors until peer stdout EOF

  bugv2
  modelcontextprotocol/python-sdk#3714 · Filter by author inanna-malick opened on Oct 14, 2026

• ClientSessionGroup leaves old tools after disconnecting a re-registered session

  bugv1v2
  modelcontextprotocol/python-sdk#3713 · Filter by author inanna-malick opened on Oct 14, 2026

• Ordinary-class structured outputs discard Annotated field constraints and accept invalid values

  bugv1v2
  modelcontextprotocol/python-sdk#3712 · Filter by author inanna-malick opened on Oct 14, 2026
  1

• Dataclass structured outputs mishandle slots and InitVar fields

  bugv1v2
  modelcontextprotocol/python-sdk#3711 · Filter by author inanna-malick opened on Oct 14, 2026

• Tool parameters model_dump and field_model_dump collide in the generated input schema

  bugv1v2
  modelcontextprotocol/python-sdk#3710 · Filter by author inanna-malick opened on Oct 14, 2026

• A synchronous prompt callback returning Awaitable is rendered as coroutine text

  bugv2
  modelcontextprotocol/python-sdk#3709 · Filter by author inanna-malick opened on Oct 14, 2026
  1

• A lone surrogate in an outgoing message silently kills the stdio server's writer or the client session

  bugv1v2
  modelcontextprotocol/python-sdk#3707 · Filter by author Yatsuiii opened on Oct 14, 2026
  1

• AuthSettings.issuer_url is required in resource-server-only mode but never used

  enhancement
  modelcontextprotocol/python-sdk#3702 · Filter by author AkshayShah03 opened on Oct 13, 2026
  1

• 2026-07-28 SSE responses share one header list, so in-place middleware appends leak across responses

  bugspec-2026-07-28v2
  modelcontextprotocol/python-sdk#3701 · Filter by author mgoldsborough opened on Oct 13, 2026
  1

• stdio_client: receiving a large response takes quadratic time (buffer + chunk is re-copied for every chunk)

  bugv1v2
  modelcontextprotocol/python-sdk#3699 · Filter by author youprint opened on Oct 13, 2026
  3

• Streamable HTTP: malformed requests return raw pydantic errors to the client

  bugv1v2
  modelcontextprotocol/python-sdk#3698 · Filter by author john-mihailescu opened on Oct 13, 2026

• 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
  2

• 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

• @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

• 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