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Running out of memory when using a combination of monkey patched asyncio.sleep and MCP Client

bugSomething isn't working. Reports of errors, unexpected behavior, or broken functionality.Something isn't working. Reports of errors, unexpected behavior, or broken functionality.

clientRelated to the FastMCP client SDK or client-side functionality.Related to the FastMCP client SDK or client-side functionality.

Status: Open.

#3895 In PrefectHQ/fastmcp;

· gediminasz opened on Apr 13, 2026

DereferenceRefsMiddleware crashes with RecursionError on JSON Pointer style $ref (non-$defs)

bugSomething isn't working. Reports of errors, unexpected behavior, or broken functionality.Something isn't working. Reports of errors, unexpected behavior, or broken functionality.

serverRelated to FastMCP server implementation or server-side functionality.Related to FastMCP server implementation or server-side functionality.

Status: Open.

#3893 In PrefectHQ/fastmcp;

· maxime-gautre opened on Apr 13, 2026

OTEL: Instrument ctx.sample() / sampling loop with spans and metrics

too-longExcessively verbose or unedited LLM output. Condense before triage.Excessively verbose or unedited LLM output. Condense before triage.

Status: Open.

#3891 In PrefectHQ/fastmcp;

· strawgate opened on Apr 13, 2026

Docs: Best practices for emitting custom spans from tools, prompts, and resources

documentationUpdates to docs, examples, or guides. Primary change is documentation-related.Updates to docs, examples, or guides. Primary change is documentation-related.

Status: Open.

#3888 In PrefectHQ/fastmcp;

· strawgate opened on Apr 13, 2026

OTEL: Instrument all MCP methods, not just tools/call, resources/read, prompts/get

clientRelated to the FastMCP client SDK or client-side functionality.Related to the FastMCP client SDK or client-side functionality.

enhancementImprovement to existing functionality. For issues and smaller PR improvements.Improvement to existing functionality. For issues and smaller PR improvements.

serverRelated to FastMCP server implementation or server-side functionality.Related to FastMCP server implementation or server-side functionality.

Status: Open.

#3887 In PrefectHQ/fastmcp;

· strawgate opened on Apr 13, 2026

OTEL: Fix attribute compliance with MCP semantic conventions

enhancementImprovement to existing functionality. For issues and smaller PR improvements.Improvement to existing functionality. For issues and smaller PR improvements.

Status: Open.

#3886 In PrefectHQ/fastmcp;

· strawgate opened on Apr 13, 2026

OAuthProxy: _refresh_locks dict grows unboundedly with token churn

authRelated to authentication (Bearer, JWT, OAuth, WorkOS) for client or server.Related to authentication (Bearer, JWT, OAuth, WorkOS) for client or server.

bugSomething isn't working. Reports of errors, unexpected behavior, or broken functionality.Something isn't working. Reports of errors, unexpected behavior, or broken functionality.

serverRelated to FastMCP server implementation or server-side functionality.Related to FastMCP server implementation or server-side functionality.

Status: Open.

#3866 In PrefectHQ/fastmcp;

· strawgate opened on Apr 12, 2026

Client bugs: elicitation scalar return, resource dict return, raise_on_error+task, Client.new() shared state, prompt error message

too-longExcessively verbose or unedited LLM output. Condense before triage.Excessively verbose or unedited LLM output. Condense before triage.

Status: Open.

#3856 In PrefectHQ/fastmcp;

· strawgate opened on Apr 11, 2026

RetryMiddleware doesn't retry tool errors because FastMCP wraps exceptions before middleware sees them

bugSomething isn't working. Reports of errors, unexpected behavior, or broken functionality.Something isn't working. Reports of errors, unexpected behavior, or broken functionality.

potential-duplicateBot-suggested duplicate awaiting human review. Auto-closes after 3 days if unchallenged.Bot-suggested duplicate awaiting human review. Auto-closes after 3 days if unchallenged.

serverRelated to FastMCP server implementation or server-side functionality.Related to FastMCP server implementation or server-side functionality.

Status: Open.

#3855 In PrefectHQ/fastmcp;

· strawgate opened on Apr 11, 2026

json_schema_to_type silently returns Any for allOf and oneOf schemas

bugSomething isn't working. Reports of errors, unexpected behavior, or broken functionality.Something isn't working. Reports of errors, unexpected behavior, or broken functionality.

openapiRelated to OpenAPI integration, parsing, or code generation features.Related to OpenAPI integration, parsing, or code generation features.

Status: Open.

#3839 In PrefectHQ/fastmcp;

· strawgate opened on Apr 11, 2026

TransformedTool: output_schema=False documented but not implemented

enhancementImprovement to existing functionality. For issues and smaller PR improvements.Improvement to existing functionality. For issues and smaller PR improvements.

serverRelated to FastMCP server implementation or server-side functionality.Related to FastMCP server implementation or server-side functionality.

Status: Open.

#3834 In PrefectHQ/fastmcp;

· strawgate opened on Apr 11, 2026

Introduce 3rd Party MCP Client/Server testing

enhancementImprovement to existing functionality. For issues and smaller PR improvements.Improvement to existing functionality. For issues and smaller PR improvements.

tests

Status: Open.

#3820 In PrefectHQ/fastmcp;

· strawgate opened on Apr 10, 2026