diff --git a/AddressCheck.cs b/AddressCheck.cs
new file mode 100644
index 0000000..f137daa
--- /dev/null
+++ b/AddressCheck.cs
@@ -0,0 +1,72 @@
+using System.Collections.Generic;
+
+namespace Logof_Client;
+
+public class AddressCheck
+{
+    public enum ErrorTypes
+    {
+        PlzTooShort,
+        PlzTooLong,
+        NoCity,
+        NoStreet,
+        NoLastName,
+        NoFirstName
+    }
+
+    public static List<(int, List<ErrorTypes>)> Perform(KasAddressList addresses)
+    {
+        var failed_refsids = new List<(int, List<ErrorTypes>)>();
+
+        foreach (var person in addresses.KasPersons)
+        {
+            var errors = new List<ErrorTypes>();
+            var hasFaults = false;
+
+
+            if (person.plz < 10000)
+            {
+                hasFaults = true;
+                errors.Add(ErrorTypes.PlzTooShort);
+            }
+
+            if (person.plz > 99999)
+            {
+                hasFaults = true;
+                errors.Add(ErrorTypes.PlzTooLong);
+            }
+
+            if (person.ort == null || person.ort == "")
+            {
+                hasFaults = true;
+                errors.Add(ErrorTypes.NoCity);
+            }
+
+            if (person.name == null || person.name == "")
+            {
+                hasFaults = true;
+                errors.Add(ErrorTypes.NoLastName);
+            }
+
+            if (person.vorname == null || person.vorname == "")
+            {
+                hasFaults = true;
+                errors.Add(ErrorTypes.NoFirstName);
+            }
+
+            if (person.strasse == null || person.strasse == "")
+            {
+                hasFaults = true;
+                errors.Add(ErrorTypes.NoStreet);
+            }
+
+            ;
+            // More errors...
+
+
+            if (hasFaults) failed_refsids.Add((person.refsid, errors));
+        }
+
+        return failed_refsids;
+    }
+}
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