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TypeError: FastMCP() got unexpected keyword argument(s): 'description'

breaking changeBreaks backward compatibility. Requires minor version bump. Critical for maintainer attention.Breaks backward compatibility. Requires minor version bump. Critical for maintainer attention.

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.

#4016 In PrefectHQ/fastmcp;

· swbuehler72 opened on Apr 22, 2026

FastMCP HTTP Stream Transport Fails with Auth0 SSO Behind AWS ALB

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.

httpRelated to HTTP transport, networking, or web server functionality.Related to HTTP transport, networking, or web server functionality.

needs MREBug reports require a copy/pastable MRE that can run as-is.Bug reports require a copy/pastable MRE that can run as-is.

Status: Open.

#4004 In PrefectHQ/fastmcp;

· sohail-norstella opened on Apr 21, 2026

OpenTelemetry: FastMCP client does not propagate trace context on initialize and list methods

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.

#3998 In PrefectHQ/fastmcp;

· strawgate opened on Apr 21, 2026

FastMCPProxy servers trigger Claude Desktop's "Authentication required to use this tool" prompt on first tool call, plain FastMCP servers don't

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.

#3996 In PrefectHQ/fastmcp;

· 7robots opened on Apr 20, 2026

Native telemetry breaks third-party OpenTelemetry instrumentations

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.

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

Status: Open.

#3993 In PrefectHQ/fastmcp;

· adityamehra opened on Apr 20, 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

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