diff --git a/src/content/ContentBuilder.cpp b/src/content/ContentBuilder.cpp
index adbe6425..723eabe1 100644
--- a/src/content/ContentBuilder.cpp
+++ b/src/content/ContentBuilder.cpp
@@ -54,6 +54,7 @@ std::unique_ptr<Content> ContentBuilder::build() {
         EntityDef& def = *entities.defs[name];
 
         // Generating runtime info
+        def.rt.id = entityDefsIndices.size();
         entityDefsIndices.push_back(&def);
     }
 
diff --git a/src/content/ContentLoader.cpp b/src/content/ContentLoader.cpp
index 265c93b7..799ef94a 100644
--- a/src/content/ContentLoader.cpp
+++ b/src/content/ContentLoader.cpp
@@ -27,38 +27,36 @@ static debug::Logger logger("content-loader");
 ContentLoader::ContentLoader(ContentPack* pack) : pack(pack) {
 }
 
+static void detect_defs(
+    const fs::path& folder,
+    const std::string& prefix,
+    std::vector<std::string>& detected
+) {
+    if (fs::is_directory(folder)) {
+        for (const auto& entry : fs::directory_iterator(folder)) {
+            const fs::path& file = entry.path();
+            std::string name = file.stem().string();
+            if (name[0] == '_') {
+                continue;
+            }
+            if (fs::is_regular_file(file) && file.extension() == ".json") {
+                detected.push_back(prefix.empty() ? name : prefix + ":" + name);
+            } else if (fs::is_directory(file)) {
+                detect_defs(file, name, detected);
+            }
+        }
+    }
+}
+
 bool ContentLoader::fixPackIndices(
     const fs::path& folder,
     dynamic::Map* indicesRoot,
     const std::string& contentSection
 ) {
     std::vector<std::string> detected;
-    std::vector<std::string> indexed;
-    if (fs::is_directory(folder)) {
-        for (const auto& entry : fs::directory_iterator(folder)) {
-            const fs::path& file = entry.path();
-            if (fs::is_regular_file(file) && file.extension() == ".json") {
-                std::string name = file.stem().string();
-                if (name[0] == '_')
-                    continue;
-                detected.push_back(name);
-            } else if (fs::is_directory(file)) {
-                std::string space = file.stem().string();
-                if (space[0] == '_')
-                    continue;
-                for (const auto& entry : fs::directory_iterator(file)) {
-                    const fs::path& file = entry.path();
-                    if (fs::is_regular_file(file) && file.extension() == ".json") {
-                        std::string name = file.stem().string();
-                        if (name[0] == '_')
-                            continue;
-                        detected.push_back(space + ':' + name);
-                    }
-                }
-            }
-        }
-    }
+    detect_defs(folder, "", detected);
 
+    std::vector<std::string> indexed;
     bool modified = false;
     if (!indicesRoot->has(contentSection)) {
         indicesRoot->putList(contentSection);
@@ -90,6 +88,7 @@ void ContentLoader::fixPackIndices() {
     auto indexFile = pack->getContentFile();
     auto blocksFolder = folder/ContentPack::BLOCKS_FOLDER;
     auto itemsFolder = folder/ContentPack::ITEMS_FOLDER;
+    auto entitiesFolder = folder/ContentPack::ENTITIES_FOLDER;
 
     dynamic::Map_sptr root;
     if (fs::is_regular_file(indexFile)) {
@@ -99,9 +98,9 @@ void ContentLoader::fixPackIndices() {
     }
 
     bool modified = false;
-
     modified |= fixPackIndices(blocksFolder, root.get(), "blocks");
     modified |= fixPackIndices(itemsFolder, root.get(), "items");
+    modified |= fixPackIndices(entitiesFolder, root.get(), "entities");
 
     if (modified){
         // rewrite modified json
diff --git a/src/content/ContentLoader.hpp b/src/content/ContentLoader.hpp
index 7a5068eb..6c04b6db 100644
--- a/src/content/ContentLoader.hpp
+++ b/src/content/ContentLoader.hpp
@@ -26,6 +26,9 @@ class ContentLoader {
     void loadCustomBlockModel(Block& def, dynamic::Map* primitives);
     void loadItem(ItemDef& def, const std::string& full, const std::string& name);
     void loadBlockMaterial(BlockMaterial& def, const fs::path& file);
+
+    void loadBlock(Block& def, const std::string& name, const fs::path& file);
+    void loadItem(ItemDef& def, const std::string& name, const fs::path& file);
 public:
     ContentLoader(ContentPack* pack);
 
@@ -35,8 +38,6 @@ public:
         const std::string& contentSection
     );
     void fixPackIndices();
-    void loadBlock(Block& def, const std::string& name, const fs::path& file);
-    void loadItem(ItemDef& def, const std::string& name, const fs::path& file);
     void load(ContentBuilder& builder);
 };
 
diff --git a/src/content/ContentPack.cpp b/src/content/ContentPack.cpp
index e3a5f0f1..8388e30c 100644
--- a/src/content/ContentPack.cpp
+++ b/src/content/ContentPack.cpp
@@ -11,10 +11,6 @@
 
 namespace fs = std::filesystem;
 
-const std::string ContentPack::PACKAGE_FILENAME = "package.json";
-const std::string ContentPack::CONTENT_FILENAME = "content.json";
-const fs::path ContentPack::BLOCKS_FOLDER = "blocks";
-const fs::path ContentPack::ITEMS_FOLDER = "items";
 const std::vector<std::string> ContentPack::RESERVED_NAMES = {
     "res", "abs", "local", "core", "user", "world", "none", "null"
 };
diff --git a/src/content/ContentPack.hpp b/src/content/ContentPack.hpp
index ca0aff2e..dfb62033 100644
--- a/src/content/ContentPack.hpp
+++ b/src/content/ContentPack.hpp
@@ -46,10 +46,11 @@ struct ContentPack {
 
     fs::path getContentFile() const;
 
-    static const std::string PACKAGE_FILENAME;
-    static const std::string CONTENT_FILENAME;
-    static const fs::path BLOCKS_FOLDER;
-    static const fs::path ITEMS_FOLDER;
+    static inline const std::string PACKAGE_FILENAME = "package.json";
+    static inline const std::string CONTENT_FILENAME = "content.json";
+    static inline const fs::path BLOCKS_FOLDER = "blocks";
+    static inline const fs::path ITEMS_FOLDER = "items";
+    static inline const fs::path ENTITIES_FOLDER = "entities";
     static const std::vector<std::string> RESERVED_NAMES;
 
     static bool is_pack(const fs::path& folder);
diff --git a/src/files/WorldFiles.cpp b/src/files/WorldFiles.cpp
index 82b70881..b497b69a 100644
--- a/src/files/WorldFiles.cpp
+++ b/src/files/WorldFiles.cpp
@@ -11,6 +11,7 @@
 #include "../lighting/Lightmap.hpp"
 #include "../maths/voxmaths.hpp"
 #include "../objects/Player.hpp"
+#include "../objects/EntityDef.hpp"
 #include "../physics/Hitbox.hpp"
 #include "../typedefs.hpp"
 #include "../settings.hpp"
@@ -92,22 +93,19 @@ void WorldFiles::writePacks(const std::vector<ContentPack>& packs) {
     files::write_string(packsFile, ss.str());
 }
 
+template<class T>
+static void write_indices(const ContentUnitIndices<T>& indices, dynamic::List& list) {
+    size_t count = indices.count();
+    for (size_t i = 0; i < count; i++) {
+        list.put(indices.get(i)->name);
+    }
+}
+
 void WorldFiles::writeIndices(const ContentIndices* indices) {
     dynamic::Map root;
-    uint count;
-    auto& blocks = root.putList("blocks");
-    count = indices->blocks.count();
-    for (uint i = 0; i < count; i++) {
-        const Block* def = indices->blocks.get(i);
-        blocks.put(def->name);
-    }
-
-    auto& items = root.putList("items");
-    count = indices->items.count();
-    for (uint i = 0; i < count; i++) {
-        items.put(indices->items.get(i)->name);
-    }
-
+    write_indices(indices->blocks, root.putList("blocks"));
+    write_indices(indices->items, root.putList("items"));
+    write_indices(indices->entities, root.putList("entities"));
     files::write_json(getIndicesFile(), &root);
 }
 
diff --git a/src/objects/EntityDef.hpp b/src/objects/EntityDef.hpp
index 06510099..70f8653b 100644
--- a/src/objects/EntityDef.hpp
+++ b/src/objects/EntityDef.hpp
@@ -8,6 +8,10 @@
 struct EntityDef {
     /// @brief Entity string id (with prefix included)
     std::string const name;
+
+    struct {
+        entityid_t id;
+    } rt;
     
     EntityDef(const std::string& name);
     EntityDef(const EntityDef&) = delete;