diff --git a/src/content/ContentLoader.cpp b/src/content/ContentLoader.cpp
index 7adb8d3b..5fe39b1b 100644
--- a/src/content/ContentLoader.cpp
+++ b/src/content/ContentLoader.cpp
@@ -24,6 +24,7 @@
 #include "data/StructLayout.hpp"
 
 namespace fs = std::filesystem;
+using namespace data;
 
 static debug::Logger logger("content-loader");
 
@@ -117,6 +118,30 @@ void ContentLoader::fixPackIndices() {
     }
 }
 
+static void perform_user_block_fields(
+    const std::string& blockName, StructLayout& layout
+) {
+    if (layout.size() > MAX_USER_BLOCK_FIELDS_SIZE) {
+        throw std::runtime_error(
+            util::quote(blockName) + 
+            " fields total size exceeds limit (" + 
+            std::to_string(layout.size()) + "/" +
+            std::to_string(MAX_USER_BLOCK_FIELDS_SIZE) + ")");
+    }
+    for (const auto& field : layout) {
+        if (field.name.at(0) == '.') {
+            throw std::runtime_error(
+                util::quote(blockName) + " field " + field.name + 
+                ": user field may not start with '.'");
+        }
+    }
+
+    std::vector<Field> fields;
+    fields.insert(fields.end(), layout.begin(), layout.end());
+    // add built-in fields here
+    layout = StructLayout::create(fields);
+}
+
 void ContentLoader::loadBlock(
     Block& def, const std::string& name, const fs::path& file
 ) {
@@ -253,15 +278,10 @@ void ContentLoader::loadBlock(
     root.at("tick-interval").get(def.tickInterval);
 
     if (root.has("fields")) {
-        def.dataStruct = std::make_unique<data::StructLayout>();
+        def.dataStruct = std::make_unique<StructLayout>();
         def.dataStruct->deserialize(root["fields"]);
-        if (def.dataStruct->size() > MAX_BLOCK_FIELDS_SIZE) {
-            throw std::runtime_error(
-                util::quote(def.name) + 
-                " fields total size exceeds limit (" + 
-                std::to_string(def.dataStruct->size()) + "/" +
-                std::to_string(MAX_BLOCK_FIELDS_SIZE) + ")");
-        }
+
+        perform_user_block_fields(def.name, *def.dataStruct);
     }
 
     if (def.tickInterval == 0) {
diff --git a/src/data/StructLayout.cpp b/src/data/StructLayout.cpp
index a7af3e91..a3e0fd23 100644
--- a/src/data/StructLayout.cpp
+++ b/src/data/StructLayout.cpp
@@ -385,7 +385,7 @@ void StructLayout::deserialize(const dv::value& src) {
                 fieldmap["convert-strategy"].asString()
             );
         }
-        fields.push_back(Field {type, name, elements, convertStrategy});
+        fields.push_back(Field (type, name, elements, convertStrategy));
     }
     *this = create(fields);
 }
diff --git a/src/data/StructLayout.hpp b/src/data/StructLayout.hpp
index 2c3ee65e..02a5a435 100644
--- a/src/data/StructLayout.hpp
+++ b/src/data/StructLayout.hpp
@@ -81,6 +81,18 @@ namespace data {
         /// @brief Byte size of the field
         int size;
 
+        Field(
+            FieldType type, 
+            std::string name, 
+            int elements, 
+            FieldConvertStrategy strategy=FieldConvertStrategy::RESET
+        ) : type(type), 
+            name(std::move(name)), 
+            elements(elements), 
+            convertStrategy(strategy),
+            offset(0),
+            size(0) {}
+
         bool operator==(const Field& o) const {
             return type == o.type && 
                    name == o.name && 
@@ -233,6 +245,14 @@ namespace data {
             return totalSize;
         }
 
+        [[nodiscard]] const auto begin() const {
+            return fields.begin();
+        }
+
+        [[nodiscard]] const auto end() const {
+            return fields.end();
+        }
+
         /// @brief Convert structure data from srcLayout to this layout.
         /// @param srcLayout source structure layout
         /// @param src source data
diff --git a/src/voxels/Block.cpp b/src/voxels/Block.cpp
index f06f052d..d09cbd99 100644
--- a/src/voxels/Block.cpp
+++ b/src/voxels/Block.cpp
@@ -1,5 +1,6 @@
 #include "Block.hpp"
 
+#include <set>
 #include <utility>
 
 #include "core_defs.hpp"
@@ -141,3 +142,10 @@ void Block::cloneTo(Block& dst) {
     dst.inventorySize = inventorySize;
     dst.tickInterval = tickInterval;
 }
+
+static std::set<std::string, std::less<>> RESERVED_BLOCK_FIELDS {
+};
+
+bool Block::isReservedBlockField(std::string_view view) {
+    return RESERVED_BLOCK_FIELDS.find(view) != RESERVED_BLOCK_FIELDS.end();
+}
diff --git a/src/voxels/Block.hpp b/src/voxels/Block.hpp
index 555d0f05..3ba6785a 100644
--- a/src/voxels/Block.hpp
+++ b/src/voxels/Block.hpp
@@ -26,7 +26,7 @@ inline constexpr uint FACE_PZ = 5;
 /// complex hitboxes
 inline constexpr uint BLOCK_AABB_GRID = 16;
 
-inline constexpr size_t MAX_BLOCK_FIELDS_SIZE = 240;
+inline constexpr size_t MAX_USER_BLOCK_FIELDS_SIZE = 240;
 
 inline std::string DEFAULT_MATERIAL = "base:stone";
 
@@ -222,6 +222,8 @@ public:
     ~Block();
 
     void cloneTo(Block& dst);
+
+    static bool isReservedBlockField(std::string_view view);
 };
 
 inline glm::ivec3 get_ground_direction(const Block& def, int rotation) {
diff --git a/test/data/StructLayout.cpp b/test/data/StructLayout.cpp
index 4933111a..37baec35 100644
--- a/test/data/StructLayout.cpp
+++ b/test/data/StructLayout.cpp
@@ -117,9 +117,9 @@ TEST(StructLayout, ConvertWithLoss) {
 
 TEST(StructLayout, Serialization) {
     std::vector<Field> fields {
-        Field {FieldType::CHAR, "text", 5},
-        Field {FieldType::I16, "someint", 1},
-        Field {FieldType::F64, "pi", 1},
+        Field (FieldType::CHAR, "text", 5),
+        Field (FieldType::I16, "someint", 1),
+        Field (FieldType::F64, "pi", 1),
     };
     auto layout1 = StructLayout::create(fields);
     auto serialized = layout1.serialize();