diff --git a/Component-DataConnectionLayer.md b/Component-DataConnectionLayer.md
index 3a5886c..1a5033a 100644
--- a/Component-DataConnectionLayer.md
+++ b/Component-DataConnectionLayer.md
@@ -54,7 +54,7 @@ Additional protocols can be added by implementing this interface.
 
 ### Common Value Type
 
-Both protocols produce the same value tuple consumed by Instance Actors:
+Both protocols produce the same value tuple consumed by Instance Actors. Before the first value update arrives from the DCL, data-sourced attributes are held at **uncertain** quality by the Instance Actor (see Site Runtime — Initialization):
 
 | Concept | ScadaLink Design | LmxProxy SDK (`Vtq`) |
 |---|---|---|
diff --git a/Component-SiteRuntime.md b/Component-SiteRuntime.md
index e929017..e85ef78 100644
--- a/Component-SiteRuntime.md
+++ b/Component-SiteRuntime.md
@@ -87,9 +87,10 @@ Deployment Manager Singleton (Cluster Singleton)
 
 ### Initialization
 1. Load all attribute values from the flattened configuration (static defaults).
-2. Register data source references with the Data Connection Layer for subscriptions.
-3. Create child Script Actors (one per script defined on the instance).
-4. Create child Alarm Actors (one per alarm defined on the instance).
+2. Set quality to **uncertain** for all attributes that have a data source reference. Static attributes (no data source reference) have quality **good**. The uncertain quality persists until the first value update arrives from the Data Connection Layer, distinguishing "not yet received" from "known good" or "connection lost."
+3. Register data source references with the Data Connection Layer for subscriptions.
+4. Create child Script Actors (one per script defined on the instance).
+5. Create child Alarm Actors (one per alarm defined on the instance).
 
 ### Attribute Value Updates
 - Receives tag value updates from the Data Connection Layer for attributes with data source references.
diff --git a/HighLevelReqs.md b/HighLevelReqs.md
index f838f78..4f13f73 100644
--- a/HighLevelReqs.md
+++ b/HighLevelReqs.md
@@ -60,6 +60,7 @@
 - Both protocols implement a **common interface** supporting: connect, subscribe to tag paths, receive value updates, and write values.
 - Additional protocols can be added by implementing the common interface.
 - The Data Connection Layer is a **clean data pipe** — it publishes tag value updates to Instance Actors but performs no evaluation of triggers or alarm conditions.
+- **Initial attribute quality**: Attributes bound to a data connection start with **uncertain** quality when the Instance Actor initializes. The quality remains uncertain until the first value update is received from the Data Connection Layer. This distinguishes "never received a value" from "received a known-good value" or "connection lost" (bad quality).
 
 ### 2.5 Scale
 - Approximately **10 sites**.
diff --git a/src/ScadaLink.Commons/Messages/Instance/GetAttributeRequest.cs b/src/ScadaLink.Commons/Messages/Instance/GetAttributeRequest.cs
index 5632646..d0caaa8 100644
--- a/src/ScadaLink.Commons/Messages/Instance/GetAttributeRequest.cs
+++ b/src/ScadaLink.Commons/Messages/Instance/GetAttributeRequest.cs
@@ -11,7 +11,9 @@ public record GetAttributeRequest(
     DateTimeOffset Timestamp);
 
 /// <summary>
-/// Response containing the current value of an attribute.
+/// Response containing the current value and quality of an attribute.
+/// Quality is "Good", "Bad", or "Uncertain".
+/// Data-sourced attributes start at "Uncertain" until the first DCL value update arrives.
 /// </summary>
 public record GetAttributeResponse(
     string CorrelationId,
@@ -19,4 +21,5 @@ public record GetAttributeResponse(
     string AttributeName,
     object? Value,
     bool Found,
+    string Quality,
     DateTimeOffset Timestamp);
diff --git a/src/ScadaLink.SiteRuntime/Actors/InstanceActor.cs b/src/ScadaLink.SiteRuntime/Actors/InstanceActor.cs
index 565d738..89be901 100644
--- a/src/ScadaLink.SiteRuntime/Actors/InstanceActor.cs
+++ b/src/ScadaLink.SiteRuntime/Actors/InstanceActor.cs
@@ -38,6 +38,7 @@ public class InstanceActor : ReceiveActor
     private readonly SiteRuntimeOptions _options;
     private readonly ILogger _logger;
     private readonly Dictionary<string, object?> _attributes = new();
+    private readonly Dictionary<string, string> _attributeQualities = new();
     private readonly Dictionary<string, AlarmState> _alarmStates = new();
     private readonly Dictionary<string, IActorRef> _scriptActors = new();
     private readonly Dictionary<string, IActorRef> _alarmActors = new();
@@ -75,11 +76,15 @@ public class InstanceActor : ReceiveActor
         _configuration = JsonSerializer.Deserialize<FlattenedConfiguration>(configJson);
 
         // Load default attribute values from the flattened configuration
+        // Data-sourced attributes start with Uncertain quality until the first DCL value arrives.
+        // Static attributes start with Good quality.
         if (_configuration != null)
         {
             foreach (var attr in _configuration.Attributes)
             {
                 _attributes[attr.CanonicalName] = attr.Value;
+                _attributeQualities[attr.CanonicalName] =
+                    string.IsNullOrEmpty(attr.DataSourceReference) ? "Good" : "Uncertain";
             }
         }
 
@@ -169,12 +174,14 @@ public class InstanceActor : ReceiveActor
     private void HandleGetAttribute(GetAttributeRequest request)
     {
         var found = _attributes.TryGetValue(request.AttributeName, out var value);
+        _attributeQualities.TryGetValue(request.AttributeName, out var quality);
         Sender.Tell(new GetAttributeResponse(
             request.CorrelationId,
             _instanceUniqueName,
             request.AttributeName,
             value,
             found,
+            quality ?? "Good",
             DateTimeOffset.UtcNow));
     }
 
@@ -249,6 +256,7 @@ public class InstanceActor : ReceiveActor
     {
         // WP-24: State mutation serialized through this actor
         _attributes[changed.AttributeName] = changed.Value;
+        _attributeQualities[changed.AttributeName] = changed.Quality;
 
         PublishAndNotifyChildren(changed);
     }
@@ -345,7 +353,7 @@ public class InstanceActor : ReceiveActor
             kvp.Key,
             kvp.Key,
             kvp.Value,
-            "Good",
+            _attributeQualities.GetValueOrDefault(kvp.Key, "Good"),
             DateTimeOffset.UtcNow)).ToList();
 
         var alarmStates = _alarmStates.Select(kvp => new AlarmStateChanged(
diff --git a/tests/ScadaLink.SiteRuntime.Tests/Actors/InstanceActorTests.cs b/tests/ScadaLink.SiteRuntime.Tests/Actors/InstanceActorTests.cs
index 8d4511a..20b5254 100644
--- a/tests/ScadaLink.SiteRuntime.Tests/Actors/InstanceActorTests.cs
+++ b/tests/ScadaLink.SiteRuntime.Tests/Actors/InstanceActorTests.cs
@@ -222,4 +222,61 @@ public class InstanceActorTests : TestKit, IDisposable
         var response = ExpectMsg<GetAttributeResponse>();
         Assert.Equal("98.6", response.Value?.ToString());
     }
+
+    [Fact]
+    public void InstanceActor_DataSourcedAttribute_StartsWithUncertainQuality()
+    {
+        var config = new FlattenedConfiguration
+        {
+            InstanceUniqueName = "Pump1",
+            Attributes =
+            [
+                new ResolvedAttribute
+                {
+                    CanonicalName = "Temperature",
+                    Value = "0",
+                    DataType = "Double",
+                    DataSourceReference = "/Motor/Temperature",
+                    BoundDataConnectionName = "OpcServer1"
+                }
+            ]
+        };
+
+        var actor = CreateInstanceActor("Pump1", config);
+
+        actor.Tell(new GetAttributeRequest(
+            "corr-quality-1", "Pump1", "Temperature", DateTimeOffset.UtcNow));
+
+        var response = ExpectMsg<GetAttributeResponse>();
+        Assert.True(response.Found);
+        Assert.Equal("Uncertain", response.Quality);
+    }
+
+    [Fact]
+    public void InstanceActor_StaticAttribute_StartsWithGoodQuality()
+    {
+        var config = new FlattenedConfiguration
+        {
+            InstanceUniqueName = "Pump1",
+            Attributes =
+            [
+                new ResolvedAttribute
+                {
+                    CanonicalName = "Label",
+                    Value = "Main Pump",
+                    DataType = "String"
+                    // No DataSourceReference — static attribute
+                }
+            ]
+        };
+
+        var actor = CreateInstanceActor("Pump1", config);
+
+        actor.Tell(new GetAttributeRequest(
+            "corr-quality-2", "Pump1", "Label", DateTimeOffset.UtcNow));
+
+        var response = ExpectMsg<GetAttributeResponse>();
+        Assert.True(response.Found);
+        Assert.Equal("Good", response.Quality);
+    }
 }