Issues

• Root object schemas ignore const and enum constraints

  bugclient
  PrefectHQ/fastmcp#5657 · Filter by author Larry-Labs opened on Oct 10, 2026

• Client drops typed additional properties from structured tool results

  bugclient
  PrefectHQ/fastmcp#5655 · Filter by author hulkbig opened on Oct 10, 2026

• your brain fucked to change import syntax???

  invalid
  PrefectHQ/fastmcp#5654 · Filter by author idontczzz opened on Oct 10, 2026

• Adopt mcp 2.3's get_tool_input_schema hook: every 2026-07-28 tools/call with arguments still runs a full middleware-wrapped tools/list

  bugserver
  PrefectHQ/fastmcp#5652 · Filter by author anormang1992 opened on Oct 9, 2026

• FileUpload and per-session visibility don't work on the 2026-07-28 protocol

  bughigh-priorityserver
  PrefectHQ/fastmcp#5650 · Filter by author zzstoatzz opened on Oct 9, 2026

• Example use case: keyless web search and page fetching with a FastMCP client

  documentationlow-priorityproposal
  PrefectHQ/fastmcp#5649 · Filter by author georgeatparallel opened on Oct 9, 2026

• Supported way to serve one server's lifespan to several HTTP apps with different auth providers

  authenhancementserver
  PrefectHQ/fastmcp#5648 · Filter by author stephaneberle9 opened on Oct 9, 2026

• Schema dereferencing changes literal $ref values in tool defaults

  bug
  PrefectHQ/fastmcp#5644 · Filter by author hulkbig opened on Oct 9, 2026

• stdio log_file is written in the Windows code page, so the log is not valid UTF-8

  bugclient
  PrefectHQ/fastmcp#5641 · Filter by author ningmao-hlyz opened on Oct 9, 2026

• Tool return type handling follow-up: non-UTF-8 bytes nested in containers (dict/list) crash the tool call; container bytes annotations still advertise an output schema

  bugserver
  PrefectHQ/fastmcp#5637 · Filter by author BlueX888 opened on Oct 9, 2026

• Tool renaming drops definitions referenced by escaped JSON Pointers

  bug
  PrefectHQ/fastmcp#5587 · Filter by author lux-liang opened on Oct 8, 2026

• Unreachable-proxy mount test depends on fixed port 9999

  bugtests
  PrefectHQ/fastmcp#5580 · Filter by author ch-z-hc opened on Oct 7, 2026

• ResponseCachingMiddleware serves one session's cached tools/call result to another session

  bughigh-prioritysecurityserver
  PrefectHQ/fastmcp#5574 · Filter by author BlueX888 opened on Oct 7, 2026

• Goose Streamable HTTP extensions are omitted from CLI discovery

  bugclilow-priority
  PrefectHQ/fastmcp#5573 · Filter by author ch-z-hc opened on Oct 7, 2026

• fastmcp dev apps file.py does not recognize app.ui() tools

  bugclimcp apps
  PrefectHQ/fastmcp#5571 · Filter by author AlyLanier opened on Oct 7, 2026

• OAuth proxy's AuthorizationHandler.handle re-reads the request form after the SDK's first read already failed, raising RuntimeError: Stream consumed as an unhandled 500

  authbug
  PrefectHQ/fastmcp#5569 · Filter by author JordanAfolabiLaw opened on Oct 7, 2026

• Improve Error Handling Documentation

  documentationserver
  PrefectHQ/fastmcp#5564 · Filter by author jeffsawatzky opened on Oct 6, 2026

• OTel: prefer AccessToken.subject over client_id for enduser.id

  authbug
  PrefectHQ/fastmcp#5563 · Filter by author omikader opened on Oct 6, 2026

• Percent-encoded local references lose hydrated types in retained output schemas

  bugclientlow-priority
  PrefectHQ/fastmcp#5560 · Filter by author HuaTNA opened on Oct 6, 2026

• Configuration helpers still discard explicit port=0

  bugclifastmcp.jsonlow-priority
  PrefectHQ/fastmcp#5559 · Filter by author dream-star-end opened on Oct 6, 2026
  1

• AzureProvider: no supported way to use a custom token verifier

  authenhancement
  PrefectHQ/fastmcp#5557 · Filter by author mkdzabel opened on Oct 6, 2026

• Sampling handlers mishandle images embedded in tool results

  bugclient
  PrefectHQ/fastmcp#5553 · Filter by author mikamikasuki opened on Oct 6, 2026

• Google GenAI sampling handler treats opaque tool-use IDs as function names

  bugclient
  PrefectHQ/fastmcp#5551 · Filter by author mikamikasuki opened on Oct 6, 2026

• Apps dev server retains unbounded MCP logs even when the panel is disabled

  buglow-prioritymcp apps
  PrefectHQ/fastmcp#5548 · Filter by author mikamikasuki opened on Oct 6, 2026

• BulkToolCaller.register_tools() ignores prefix and separator

  bugcontrib
  PrefectHQ/fastmcp#5546 · Filter by author mikamikasuki opened on Oct 6, 2026