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feat: add tool lifecycle hooks (setup/teardown) for resource cleanup on cancellation

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.

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

Status: Open.

#4340 In PrefectHQ/fastmcp;

· tcconnally opened on Jun 20, 2026

Invalid URL printed to log when using IPv6

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.

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

Status: Open.

#4339 In PrefectHQ/fastmcp;

· Leseratte10 opened on Jun 20, 2026

python -m startup causes list_tools to return truncated results

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

needs more infoIssue lacks detail to reproduce or understand. Waiting for reporter to provide context.Issue lacks detail to reproduce or understand. Waiting for reporter to provide context.

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

Status: Open.

#4338 In PrefectHQ/fastmcp;

· yysdashe opened on Jun 19, 2026

ListToolsRequest validation error: "core/list" is not a valid method in mcp.types

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

high-priority

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

Status: Open.

#4337 In PrefectHQ/fastmcp;

· moumed opened on Jun 19, 2026

bug: CancelledError during tool execution silently discards partial result and leaks MCP server resources

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.

#4336 In PrefectHQ/fastmcp;

· tcconnally opened on Jun 19, 2026

Feature: Allow for custom MCP server responses when tool-level scope validation fails

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

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

Status: Open.

#4334 In PrefectHQ/fastmcp;

· gaokevin1 opened on Jun 19, 2026

fastmcp.types docstrings render as raw RST on the published SDK docs page

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

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

Status: Open.

#4331 In PrefectHQ/fastmcp;

· justinvzyl opened on Jun 17, 2026

expand_uri_template and match_uri_template do not round-trip path values containing reserved characters

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.

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

Status: Open.

#4326 In PrefectHQ/fastmcp;

· Sujit-1509 opened on Jun 15, 2026

FastMCP StatefulProxyClient.clear() can cause KeyError during proxy session teardown

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.

#4321 In PrefectHQ/fastmcp;

· mvgadagi opened on Jun 13, 2026

RateLimitingMiddleware.get_client_id passing an async callable silently disables rate limiting

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.

#4320 In PrefectHQ/fastmcp;

· Chotom opened on Jun 13, 2026

No guardrails against destructive tool capabilities (shell exec, file deletion, env access)

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.

#4318 In PrefectHQ/fastmcp;

· tcconnally opened on Jun 13, 2026

Security: Arbitrary Python Module Execution via FileSystemSource

invalidIssue lacks info, is off-topic, or doesn't make sense. Often LLM-generated spam.Issue lacks info, is off-topic, or doesn't make sense. Often LLM-generated spam.

Status: Open.

#4315 In PrefectHQ/fastmcp;

· nkar123412-hub opened on Jun 11, 2026