diff --git a/IMPLEMENTATION.md b/IMPLEMENTATION.md
index f82009e..66ede0e 100644
--- a/IMPLEMENTATION.md
+++ b/IMPLEMENTATION.md
@@ -47,7 +47,7 @@ Each type lives in `src/FrameProcessor/Domain/`. Tests in `tests/FrameProcessor.
 - JSON converter + `IParsable`.
 - **Tests:** `FrameNameTests` — accepts URL-safe, rejects whitespace/reserved chars with clear message.
 
-### [ ] 1.3 `Orientation`
+### [x] 1.3 `Orientation`
 - `enum { Landscape, Portrait }`.
 - JSON converter reading/writing kebab-case lowercase.
 
diff --git a/src/FrameProcessor/Domain/Orientation.cs b/src/FrameProcessor/Domain/Orientation.cs
new file mode 100644
index 0000000..4b991b6
--- /dev/null
+++ b/src/FrameProcessor/Domain/Orientation.cs
@@ -0,0 +1,34 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace FrameProcessor.Domain;
+
+[JsonConverter(typeof(OrientationJsonConverter))]
+public enum Orientation
+{
+    Landscape,
+    Portrait,
+}
+
+internal sealed class OrientationJsonConverter : JsonConverter<Orientation>
+{
+    public override Orientation Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+    {
+        var s = reader.GetString();
+        return s switch
+        {
+            "landscape" => Orientation.Landscape,
+            "portrait" => Orientation.Portrait,
+            _ => throw new JsonException(
+                $"'{s}' is not a valid orientation. Expected 'landscape' or 'portrait'."),
+        };
+    }
+
+    public override void Write(Utf8JsonWriter writer, Orientation value, JsonSerializerOptions options)
+        => writer.WriteStringValue(value switch
+        {
+            Orientation.Landscape => "landscape",
+            Orientation.Portrait => "portrait",
+            _ => throw new JsonException($"Unknown orientation: {value}."),
+        });
+}
diff --git a/tests/FrameProcessor.Tests/OrientationTests.cs b/tests/FrameProcessor.Tests/OrientationTests.cs
new file mode 100644
index 0000000..d63fad2
--- /dev/null
+++ b/tests/FrameProcessor.Tests/OrientationTests.cs
@@ -0,0 +1,46 @@
+using System.Text.Json;
+using FrameProcessor.Domain;
+
+namespace FrameProcessor.Tests;
+
+public class OrientationTests
+{
+    [Theory]
+    [InlineData("\"landscape\"", Orientation.Landscape)]
+    [InlineData("\"portrait\"", Orientation.Portrait)]
+    public void JsonDeserialize_KebabCaseLowercase(string json, Orientation expected)
+    {
+        var value = JsonSerializer.Deserialize<Orientation>(json);
+        Assert.Equal(expected, value);
+    }
+
+    [Theory]
+    [InlineData(Orientation.Landscape, "\"landscape\"")]
+    [InlineData(Orientation.Portrait, "\"portrait\"")]
+    public void JsonSerialize_KebabCaseLowercase(Orientation value, string expected)
+    {
+        var json = JsonSerializer.Serialize(value);
+        Assert.Equal(expected, json);
+    }
+
+    [Theory]
+    [InlineData("\"Landscape\"")]
+    [InlineData("\"PORTRAIT\"")]
+    [InlineData("\"diagonal\"")]
+    [InlineData("\"\"")]
+    public void JsonDeserialize_RejectsInvalid(string json)
+    {
+        Assert.Throws<JsonException>(() => JsonSerializer.Deserialize<Orientation>(json));
+    }
+
+    [Fact]
+    public void JsonRoundTrip_PreservesValue()
+    {
+        foreach (var value in new[] { Orientation.Landscape, Orientation.Portrait })
+        {
+            var json = JsonSerializer.Serialize(value);
+            var roundTripped = JsonSerializer.Deserialize<Orientation>(json);
+            Assert.Equal(value, roundTripped);
+        }
+    }
+}