diff --git a/weed/admin/dash/plugin_api.go b/weed/admin/dash/plugin_api.go
index e3b64fa02..44d72ac63 100644
--- a/weed/admin/dash/plugin_api.go
+++ b/weed/admin/dash/plugin_api.go
@@ -235,6 +235,9 @@ func (s *AdminServer) GetPluginJobTypeConfigAPI(w http.ResponseWriter, r *http.R
 			AdminRuntime:       &plugin_pb.AdminRuntimeConfig{},
 		}
 	}
+	if descriptor, err := s.LoadPluginJobTypeDescriptor(jobType); err == nil && descriptor != nil {
+		applyDescriptorDefaultsToPersistedConfig(config, descriptor)
+	}
 
 	renderProtoJSON(w, http.StatusOK, config)
 }
@@ -737,6 +740,90 @@ func buildJobSpecFromProposal(jobType string, proposal *plugin_pb.JobProposal, i
 	return jobSpec
 }
 
+func applyDescriptorDefaultsToPersistedConfig(
+	config *plugin_pb.PersistedJobTypeConfig,
+	descriptor *plugin_pb.JobTypeDescriptor,
+) {
+	if config == nil || descriptor == nil {
+		return
+	}
+
+	if config.AdminConfigValues == nil {
+		config.AdminConfigValues = map[string]*plugin_pb.ConfigValue{}
+	}
+	if config.WorkerConfigValues == nil {
+		config.WorkerConfigValues = map[string]*plugin_pb.ConfigValue{}
+	}
+	if config.AdminRuntime == nil {
+		config.AdminRuntime = &plugin_pb.AdminRuntimeConfig{}
+	}
+
+	if descriptor.AdminConfigForm != nil {
+		for key, value := range descriptor.AdminConfigForm.DefaultValues {
+			if value == nil {
+				continue
+			}
+			current := config.AdminConfigValues[key]
+			if current == nil {
+				config.AdminConfigValues[key] = proto.Clone(value).(*plugin_pb.ConfigValue)
+				continue
+			}
+			if strings.EqualFold(descriptor.JobType, "admin_script") &&
+				key == "script" &&
+				isBlankStringConfigValue(current) {
+				config.AdminConfigValues[key] = proto.Clone(value).(*plugin_pb.ConfigValue)
+			}
+		}
+	}
+	if descriptor.WorkerConfigForm != nil {
+		for key, value := range descriptor.WorkerConfigForm.DefaultValues {
+			if value == nil {
+				continue
+			}
+			if config.WorkerConfigValues[key] != nil {
+				continue
+			}
+			config.WorkerConfigValues[key] = proto.Clone(value).(*plugin_pb.ConfigValue)
+		}
+	}
+	if descriptor.AdminRuntimeDefaults != nil {
+		runtime := config.AdminRuntime
+		defaults := descriptor.AdminRuntimeDefaults
+		if runtime.DetectionIntervalSeconds <= 0 {
+			runtime.DetectionIntervalSeconds = defaults.DetectionIntervalSeconds
+		}
+		if runtime.DetectionTimeoutSeconds <= 0 {
+			runtime.DetectionTimeoutSeconds = defaults.DetectionTimeoutSeconds
+		}
+		if runtime.MaxJobsPerDetection <= 0 {
+			runtime.MaxJobsPerDetection = defaults.MaxJobsPerDetection
+		}
+		if runtime.GlobalExecutionConcurrency <= 0 {
+			runtime.GlobalExecutionConcurrency = defaults.GlobalExecutionConcurrency
+		}
+		if runtime.PerWorkerExecutionConcurrency <= 0 {
+			runtime.PerWorkerExecutionConcurrency = defaults.PerWorkerExecutionConcurrency
+		}
+		if runtime.RetryBackoffSeconds <= 0 {
+			runtime.RetryBackoffSeconds = defaults.RetryBackoffSeconds
+		}
+		if runtime.RetryLimit < 0 {
+			runtime.RetryLimit = defaults.RetryLimit
+		}
+	}
+}
+
+func isBlankStringConfigValue(value *plugin_pb.ConfigValue) bool {
+	if value == nil {
+		return true
+	}
+	kind, ok := value.Kind.(*plugin_pb.ConfigValue_StringValue)
+	if !ok {
+		return false
+	}
+	return strings.TrimSpace(kind.StringValue) == ""
+}
+
 func parsePositiveInt(raw string, defaultValue int) int {
 	value, err := strconv.Atoi(strings.TrimSpace(raw))
 	if err != nil || value <= 0 {
diff --git a/weed/admin/dash/plugin_api_test.go b/weed/admin/dash/plugin_api_test.go
index c4f1b74e9..200003bf5 100644
--- a/weed/admin/dash/plugin_api_test.go
+++ b/weed/admin/dash/plugin_api_test.go
@@ -31,3 +31,83 @@ func TestBuildJobSpecFromProposalDoesNotReuseProposalID(t *testing.T) {
 		t.Fatalf("dedupe key must be preserved: got=%s want=%s", jobA.DedupeKey, proposal.DedupeKey)
 	}
 }
+
+func TestApplyDescriptorDefaultsToPersistedConfigBackfillsAdminDefaults(t *testing.T) {
+	t.Parallel()
+
+	config := &plugin_pb.PersistedJobTypeConfig{
+		JobType:            "admin_script",
+		AdminConfigValues:  map[string]*plugin_pb.ConfigValue{},
+		WorkerConfigValues: map[string]*plugin_pb.ConfigValue{},
+		AdminRuntime:       &plugin_pb.AdminRuntimeConfig{},
+	}
+	descriptor := &plugin_pb.JobTypeDescriptor{
+		JobType: "admin_script",
+		AdminConfigForm: &plugin_pb.ConfigForm{
+			DefaultValues: map[string]*plugin_pb.ConfigValue{
+				"script": {
+					Kind: &plugin_pb.ConfigValue_StringValue{StringValue: "volume.balance -apply"},
+				},
+				"run_interval_minutes": {
+					Kind: &plugin_pb.ConfigValue_Int64Value{Int64Value: 17},
+				},
+			},
+		},
+		AdminRuntimeDefaults: &plugin_pb.AdminRuntimeDefaults{
+			DetectionIntervalSeconds: 60,
+			DetectionTimeoutSeconds:  300,
+		},
+	}
+
+	applyDescriptorDefaultsToPersistedConfig(config, descriptor)
+
+	script := config.AdminConfigValues["script"]
+	if script == nil {
+		t.Fatalf("expected script default to be backfilled")
+	}
+	scriptKind, ok := script.Kind.(*plugin_pb.ConfigValue_StringValue)
+	if !ok || scriptKind.StringValue == "" {
+		t.Fatalf("expected non-empty script default, got=%+v", script)
+	}
+	if config.AdminRuntime.DetectionIntervalSeconds != 60 {
+		t.Fatalf("expected runtime detection interval default to be backfilled")
+	}
+}
+
+func TestApplyDescriptorDefaultsToPersistedConfigReplacesBlankAdminScript(t *testing.T) {
+	t.Parallel()
+
+	config := &plugin_pb.PersistedJobTypeConfig{
+		JobType: "admin_script",
+		AdminConfigValues: map[string]*plugin_pb.ConfigValue{
+			"script": {
+				Kind: &plugin_pb.ConfigValue_StringValue{StringValue: "   "},
+			},
+		},
+		AdminRuntime: &plugin_pb.AdminRuntimeConfig{},
+	}
+	descriptor := &plugin_pb.JobTypeDescriptor{
+		JobType: "admin_script",
+		AdminConfigForm: &plugin_pb.ConfigForm{
+			DefaultValues: map[string]*plugin_pb.ConfigValue{
+				"script": {
+					Kind: &plugin_pb.ConfigValue_StringValue{StringValue: "volume.fix.replication -apply"},
+				},
+			},
+		},
+	}
+
+	applyDescriptorDefaultsToPersistedConfig(config, descriptor)
+
+	script := config.AdminConfigValues["script"]
+	if script == nil {
+		t.Fatalf("expected script config value")
+	}
+	scriptKind, ok := script.Kind.(*plugin_pb.ConfigValue_StringValue)
+	if !ok {
+		t.Fatalf("expected string script config value, got=%T", script.Kind)
+	}
+	if scriptKind.StringValue != "volume.fix.replication -apply" {
+		t.Fatalf("expected blank script to be replaced by default, got=%q", scriptKind.StringValue)
+	}
+}