typeServerToolstruct {Tool              mcp.ToolToolsetToolsetMetadataHandlerFuncHandlerFuncFeatureFlagEnablestringFeatureFlagDisablestring// Enabled is an optional function called at build/filter time to determine// if this tool should be available. If nil, the tool is considered enabled// (subject to FeatureFlagEnable/FeatureFlagDisable checks).// The context carries request-scoped information for the consumer to use.// Returns (enabled, error). On error, the tool should be treated as disabled.Enabledfunc(ctx context.Context) (bool,error)}

// ToolFilter is a function that determines if a tool should be included.// Returns true if the tool should be included, false to exclude it.typeToolFilterfunc(ctx context.Context,tool*ServerTool) (bool,error)// WithFilter adds a filter function that will be applied to all tools.// Multiple filters can be added and are evaluated in order.// If any filter returns false or an error, the tool is excluded.func (b*Builder)WithFilter(filterToolFilter)*Builder {b.filters=append(b.filters,filter)returnb}

// FilteredTools returns tools filtered by the Enabled function and builder filters.// This should be called per-request with the request context.func (r*Registry)FilteredTools(ctx context.Context) ([]ServerTool,error)

// Tool with self-filtering logictool:= registry.ServerTool{Tool:myTool,Toolset:myToolset,HandlerFunc:myHandler,Enabled:func(ctx context.Context) (bool,error) {// Consumer's domain-specific logic hereuser:=mypackage.UserFromContext(ctx)returnuser!=nil&&user.HasPermission("use_tool"),nil    },}// Builder with cross-cutting filterreg:=registry.NewBuilder().SetTools(tools).WithFilter(func(ctx context.Context,tool*registry.ServerTool) (bool,error) {// Cross-cutting concern like scope filteringreturn!shouldHideForCurrentAuth(ctx,tool),nil    }).Build()// Get filtered tools for a requestenabledTools,err:=reg.FilteredTools(ctx)