🚧 WIP

src/opcda_diagnozer/config.py

@@ -276,9 +276,11 @@ def _validate(config: Config) -> None:
         )
     if config.opc.connect_timeout_s <= 0:
         raise ConfigError(f"opc.connect_timeout_s: must be > 0, got {config.opc.connect_timeout_s}")
-    if not config.tags:
+    if not config.tags and not config.devices:
         raise ConfigError(
-            "tags: at least one tag is required — without tags there is nothing to monitor"
+            "tags: nothing to monitor - define at least one tag or device "
+            "indicator (devices: entries alone are fine, tags: entries alone "
+            "are fine; both empty means the tool would read nothing)"
         )
     names = [t.name for t in config.tags]
     duplicates = sorted({n for n in names if names.count(n) > 1})