diff --git a/src/GameCult.Caching.MessagePack/CultMathJson.cs b/src/GameCult.Caching.MessagePack/CultMathJson.cs
index dfd15c7f..ba83410d 100644
--- a/src/GameCult.Caching.MessagePack/CultMathJson.cs
+++ b/src/GameCult.Caching.MessagePack/CultMathJson.cs
@@ -14,7 +14,7 @@ namespace GameCult.Caching.MessagePack;
 /// The canonical System.Text.Json shape of every public CultMath value type, the JSON twin of
 /// <see cref="CultMathResolver"/>. Vectors, quaternions and colors are objects keyed by their
 /// field names (<c>{"x":1,"y":2}</c>), matrices are arrays of row objects, <c>rect</c> is
-/// <c>{"min":..,"max":..}</c>, <c>CultCellular</c> is <c>{"nearest":..,"edge":..,"id":..}</c>, <c>CultPhasor</c> is <c>{"cos":..,"sin":..}</c>, <c>SpanNoise</c> is <c>{"field":..,"curvature":..,"fold":..}</c>, <c>SpanPath</c> is <c>{"midpoint":..,"velocity":..,"speed":..,"acceleration":..,"halfLength":..}</c>, and <c>SpanStage</c> is <c>{"frequency":..,"stretch":..,"axis":..,"shift":..,"offset":..,"octaveStep":..}</c>.
+/// <c>{"min":..,"max":..}</c>, <c>CultCellular</c> is <c>{"nearest":..,"edge":..,"id":..}</c>, <c>CultPhasor</c> is <c>{"cos":..,"sin":..}</c>, <c>SpanNoise</c> is <c>{"field":..,"curvature":..,"fold":..}</c>, <c>SpanPath</c> is <c>{"midpoint":..,"velocity":..,"speed":..,"acceleration":..,"halfLength":..}</c>, <c>SpanStage</c> is <c>{"frequency":..,"stretch":..,"axis":..,"shift":..,"offset":..,"octaveStep":..}</c>, and <c>CultSiteCells</c> is <c>{"nearest":..,"second":..,"nearestSite":..,"secondSite":..}</c>.
 /// Property names are fixed: <c>PropertyNamingPolicy</c> does not rename them, and
 /// <c>PropertyNameCaseInsensitive</c> makes reading case-insensitive.
 /// <para>
@@ -481,7 +481,7 @@ public static class CultMathJson
             Add<Random, uint>(UIntScalar.Instance, new Fields<uint>(("state", Val<uint>())),
                 a => new Random { state = a[0] }, (v, a) => a[0] = v.state),
 
-            // Compositions: matrices are arrays of row objects, rect is {min, max}, CultCellular is {nearest, edge, id}, CultPhasor is {cos, sin}, SpanNoise is {field, curvature, fold}, SpanPath is {midpoint, velocity, speed, acceleration, halfLength}, SpanStage is {frequency, stretch, axis, shift, offset, octaveStep}.
+            // Compositions: matrices are arrays of row objects, rect is {min, max}, CultCellular is {nearest, edge, id}, CultPhasor is {cos, sin}, SpanNoise is {field, curvature, fold}, SpanPath is {midpoint, velocity, speed, acceleration, halfLength}, SpanStage is {frequency, stretch, axis, shift, offset, octaveStep}, CultSiteCells is {nearest, second, nearestSite, secondSite}.
             Add<float2x2, float>(f, new Rows<float>(2, Xy<float>()),
                 a => new float2x2(a[0], a[1], a[2], a[3]),
                 (v, a) => { a[0] = v[0].x; a[1] = v[0].y; a[2] = v[1].x; a[3] = v[1].y; }),
@@ -539,6 +539,14 @@ public static class CultMathJson
                     a[8] = v.offset.x; a[9] = v.offset.y; a[10] = v.offset.z;
                     a[11] = v.octaveStep.x; a[12] = v.octaveStep.y; a[13] = v.octaveStep.z;
                 }),
+            Add<CultSiteCells, float>(f, new Fields<float>(("nearest", Xyzw<float>()), ("second", Xyzw<float>()), ("nearestSite", Val<float>()), ("secondSite", Val<float>())),
+                a => new CultSiteCells(new float4(a[0], a[1], a[2], a[3]), new float4(a[4], a[5], a[6], a[7]), a[8], a[9]),
+                (v, a) =>
+                {
+                    a[0] = v.nearest.x; a[1] = v.nearest.y; a[2] = v.nearest.z; a[3] = v.nearest.w;
+                    a[4] = v.second.x; a[5] = v.second.y; a[6] = v.second.z; a[7] = v.second.w;
+                    a[8] = v.nearestSite; a[9] = v.secondSite;
+                }),
         };
 
         var map = new Dictionary<Type, JsonConverter>();
diff --git a/src/GameCult.Caching.MessagePack/CultMathResolver.cs b/src/GameCult.Caching.MessagePack/CultMathResolver.cs
index 8f287a5c..95937282 100644
--- a/src/GameCult.Caching.MessagePack/CultMathResolver.cs
+++ b/src/GameCult.Caching.MessagePack/CultMathResolver.cs
@@ -180,7 +180,7 @@ public sealed class CultMathResolver : IFormatterResolver
                     return value;
                 }),
 
-            // Compositions: matrices are rows, rect is [min, max], CultCellular is [nearest, edge, id], CultPhasor is [cos, sin], SpanNoise is [field, curvature, fold], SpanPath is [midpoint, velocity, speed, acceleration, halfLength], SpanStage is [frequency, stretch, axis, shift, offset, octaveStep].
+            // Compositions: matrices are rows, rect is [min, max], CultCellular is [nearest, edge, id], CultPhasor is [cos, sin], SpanNoise is [field, curvature, fold], SpanPath is [midpoint, velocity, speed, acceleration, halfLength], SpanStage is [frequency, stretch, axis, shift, offset, octaveStep], CultSiteCells is [nearest, second, nearestSite, secondSite].
             Shape<float2x2>((ref MessagePackWriter w, float2x2 v) => { w.WriteArrayHeader(2); PutFloat2(ref w, v[0]); PutFloat2(ref w, v[1]); },
                 (ref MessagePackReader r) =>
                 {
@@ -289,6 +289,23 @@ public sealed class CultMathResolver : IFormatterResolver
                     }
                     return value;
                 }),
+            Shape<CultSiteCells>((ref MessagePackWriter w, CultSiteCells v) => { w.WriteArrayHeader(4); PutFloat4(ref w, v.nearest); PutFloat4(ref w, v.second); w.Write(v.nearestSite); w.Write(v.secondSite); },
+                (ref MessagePackReader r) =>
+                {
+                    var value = default(CultSiteCells);
+                    for (int i = 0, n = r.ReadArrayHeader(); i < n; i++)
+                    {
+                        switch (i)
+                        {
+                            case 0: value.nearest = GetFloat4(ref r); break;
+                            case 1: value.second = GetFloat4(ref r); break;
+                            case 2: value.nearestSite = r.ReadSingle(); break;
+                            case 3: value.secondSite = r.ReadSingle(); break;
+                            default: r.Skip(); break;
+                        }
+                    }
+                    return value;
+                }),
         };
 
         var map = new Dictionary<Type, object>();
diff --git a/src/GameCult.Caching.MessagePack/README.md b/src/GameCult.Caching.MessagePack/README.md
index acb1142f..a03a67c4 100644
--- a/src/GameCult.Caching.MessagePack/README.md
+++ b/src/GameCult.Caching.MessagePack/README.md
@@ -102,6 +102,7 @@ broken graph whole (an `ExprGraphException` naming the rule), so a consumer
 | `rect` | `[min, max]` of `float2` | `{"min":{..},"max":{..}}` |
 | `CultCellular` | `[nearest, edge, id]` | `{"nearest":{..},"edge":{..},"id":..}` |
 | `CultPhasor` | `[cos, sin]` of `float4` | `{"cos":{..},"sin":{..}}` |
+| `CultSiteCells` | `[nearest, second, nearestSite, secondSite]` | `{"nearest":{..},"second":{..},"nearestSite":..,"secondSite":..}` |
 
 Floats are MessagePack float32 (`0xCA`), doubles float64 (`0xCB`), integers the
 shortest MessagePack integer.
diff --git a/tests/GameCult.Caching.Tests/CultMathJsonTests.cs b/tests/GameCult.Caching.Tests/CultMathJsonTests.cs
index 2920c2f3..4ebd552b 100644
--- a/tests/GameCult.Caching.Tests/CultMathJsonTests.cs
+++ b/tests/GameCult.Caching.Tests/CultMathJsonTests.cs
@@ -51,6 +51,8 @@ namespace GameCult.Caching.Tests
                 """{"midpoint":{"x":1,"y":2,"z":3},"velocity":{"x":4,"y":5,"z":6},"speed":7,"acceleration":8,"halfLength":9}""");
             Json(new SpanStage { frequency = 1f, stretch = 2f, axis = new float3(3f, 4f, 5f), shift = new float3(6f, 7f, 8f), offset = new float3(9f, 10f, 11f), octaveStep = new float3(12f, 13f, 14f) }).Should().Be(
                 """{"frequency":1,"stretch":2,"axis":{"x":3,"y":4,"z":5},"shift":{"x":6,"y":7,"z":8},"offset":{"x":9,"y":10,"z":11},"octaveStep":{"x":12,"y":13,"z":14}}""");
+            Json(new CultSiteCells(new float4(1, 2, 3, 4), new float4(5, 6, 7, 8), 9f, 10f)).Should().Be(
+                """{"nearest":{"x":1,"y":2,"z":3,"w":4},"second":{"x":5,"y":6,"z":7,"w":8},"nearestSite":9,"secondSite":10}""");
         }
 
         [Test]
@@ -78,6 +80,8 @@ namespace GameCult.Caching.Tests
             RoundTrip(new SpanNoise(new float4(1, 2, 3, 4), 0.25f, 0.5f));
             RoundTrip(new SpanPath { midpoint = new float3(1f, 2f, 3f), velocity = new float3(4f, 5f, 6f), speed = 7f, acceleration = 8f, halfLength = 9f });
             RoundTrip(new SpanStage { frequency = 1f, stretch = 2f, axis = new float3(3f, 4f, 5f), shift = new float3(6f, 7f, 8f), offset = new float3(9f, 10f, 11f), octaveStep = new float3(12f, 13f, 14f) });
+            RoundTrip(new CultSiteCells(new float4(1, 2, 3, 4), new float4(5, 6, 7, 8), 9f, 10f));
+            RoundTrip(new CultSiteCells(new float4(0, 0, 0, 1.0e30f), new float4(0, 0, 0, 1.0e30f), -1f, -1f));
         }
 
         [Test]
diff --git a/tests/GameCult.Caching.Tests/CultMathSerializationTests.cs b/tests/GameCult.Caching.Tests/CultMathSerializationTests.cs
index 1882bb80..c55154fb 100644
--- a/tests/GameCult.Caching.Tests/CultMathSerializationTests.cs
+++ b/tests/GameCult.Caching.Tests/CultMathSerializationTests.cs
@@ -105,6 +105,8 @@ namespace GameCult.Caching.Tests
             RoundTrip(new SpanNoise(new float4(1, 2, 3, 4), 0.25f, 0.5f));
             RoundTrip(new SpanPath { midpoint = new float3(1f, 2f, 3f), velocity = new float3(4f, 5f, 6f), speed = 7f, acceleration = 8f, halfLength = 9f });
             RoundTrip(new SpanStage { frequency = 1f, stretch = 2f, axis = new float3(3f, 4f, 5f), shift = new float3(6f, 7f, 8f), offset = new float3(9f, 10f, 11f), octaveStep = new float3(12f, 13f, 14f) });
+            RoundTrip(new CultSiteCells(new float4(1, 2, 3, 4), new float4(5, 6, 7, 8), 9f, 10f));
+            RoundTrip(new CultSiteCells(new float4(0, 0, 0, 1.0e30f), new float4(0, 0, 0, 1.0e30f), -1f, -1f));
         }
 
         [Test]
@@ -158,6 +160,12 @@ namespace GameCult.Caching.Tests
                 "93CA40C00000CA40E00000CA41000000" +
                 "93CA41100000CA41200000CA41300000" +
                 "93CA41400000CA41500000CA41600000");
+            Hex(new CultSiteCells(new float4(1, 2, 3, 4), new float4(5, 6, 7, 8), 9f, 10f)).Should().Be(
+                "94" +
+                "94CA3F800000CA40000000CA40400000CA40800000" +
+                "94CA40A00000CA40C00000CA40E00000CA41000000" +
+                "CA41100000" +
+                "CA41200000");
         }
 
         [Test]