diff --git a/hbd/server/threshold.py b/hbd/server/threshold.py
index 1bcbb8a..5a4e21f 100644
--- a/hbd/server/threshold.py
+++ b/hbd/server/threshold.py
@@ -1026,7 +1026,12 @@ class ThresholdChecker:
                 for pool_name, pool_metrics in pools.items():
                     if not isinstance(pool_metrics, dict):
                         continue
-                    for metric_name, value in pool_metrics.items():
+                    # Synthesize health_ok from health string for older clients
+                    # that predate the health_ok field.
+                    pool_metrics_effective = dict(pool_metrics)
+                    if "health" in pool_metrics and "health_ok" not in pool_metrics:
+                        pool_metrics_effective["health_ok"] = 1 if pool_metrics["health"] == "ONLINE" else 0
+                    for metric_name, value in pool_metrics_effective.items():
                         # Try specific pool name first, then wildcard '*'
                         metric_path = f"{plugin_name}.{pool_name}.{metric_name}"
                         wildcard_path = f"{plugin_name}.*.{metric_name}"
@@ -1043,7 +1048,7 @@ class ThresholdChecker:
                         elif new_level == AlertLevel.WARNING and threshold.warning is not None:
                             threshold_value = threshold.warning
                         alert_state.hysteresis = threshold.hysteresis if new_level != AlertLevel.OK else None
-                        pool_context = dict(pool_metrics)
+                        pool_context = dict(pool_metrics_effective)
                         pool_context["pool_name"] = pool_name
                         old_level = alert_state.level
                         if alert_state.update(new_level, value, threshold_value, threshold.operator.value):