diff --git a/res/project.toml b/res/project.toml
index b641ad00f..281964857 100644
--- a/res/project.toml
+++ b/res/project.toml
@@ -3,5 +3,6 @@ name = "default"
 base_packs = ["base"]
 permissions = [
     "network",
-    "record-audio"
+    "record-audio",
+    "sub-instances",
 ]
diff --git a/src/constants.hpp b/src/constants.hpp
index f43314f4a..0396f59a6 100644
--- a/src/constants.hpp
+++ b/src/constants.hpp
@@ -16,6 +16,8 @@ inline constexpr bool ENGINE_DEBUG_BUILD = true;
 
 inline const std::string ENGINE_VERSION_STRING = "0.32";
 
+inline constexpr uint MAX_SUBPROCESS_DEPTH = 2;
+
 /// @brief world regions format version
 inline constexpr uint REGION_FORMAT_VERSION = 3;
 
diff --git a/src/devtools/Project.hpp b/src/devtools/Project.hpp
index 4906b9373..571a8b2c5 100644
--- a/src/devtools/Project.hpp
+++ b/src/devtools/Project.hpp
@@ -13,6 +13,7 @@ struct Permissions {
     static inline std::string NETWORK = "network";
     static inline std::string RECORD_AUDIO = "record-audio";
     static inline std::string WRITE_TO_USER = "write-to-user";
+    static inline std::string SUB_INSTANCES = "sub-instances";
 
     std::set<std::string> permissions;
 
diff --git a/src/engine/CoreParameters.hpp b/src/engine/CoreParameters.hpp
index b9f585f47..b5d8074ce 100644
--- a/src/engine/CoreParameters.hpp
+++ b/src/engine/CoreParameters.hpp
@@ -14,5 +14,6 @@ struct CoreParameters {
     std::filesystem::path projectFolder;
     std::string debugServerString;
     int tps = 20;
+    int subProcessDepth = 0;
     std::unordered_map<std::string, std::string> projectArgs;
 };
diff --git a/src/logic/scripting/lua/libs/libapp.cpp b/src/logic/scripting/lua/libs/libapp.cpp
index 4d932c272..e3d41d8c7 100644
--- a/src/logic/scripting/lua/libs/libapp.cpp
+++ b/src/logic/scripting/lua/libs/libapp.cpp
@@ -341,6 +341,10 @@ static int l_start_debug_instance(lua::State* L) {
     if (!engine->getProject().permissions.has(Permissions::DEBUGGING)) {
         throw std::runtime_error("project has no debugging permission");
     }
+    const auto& params = engine->getCoreParameters();
+    if (params.subProcessDepth >= MAX_SUBPROCESS_DEPTH) {
+        throw std::runtime_error("max subprocess depth exceeded");
+    }
 
     int port = lua::tointeger(L, 1);
     if (port == 0) {
@@ -361,6 +365,8 @@ static int l_start_debug_instance(lua::State* L) {
         "--res", paths.getResourcesFolder().u8string(),
         "--dir", paths.getUserFilesFolder().u8string(),
         "--dbg-server",  "tcp:" + std::to_string(port),
+        "--sub-depth", std::to_string(engine->getCoreParameters()
+            .subProcessDepth + 1),
     };
     if (!projectPath.empty()) {
         args.emplace_back("--project");
@@ -376,15 +382,25 @@ static int l_start_debug_instance(lua::State* L) {
 }
 
 static int l_start_background_instance(lua::State* L) {
+    if (!engine->getProject().permissions.has(Permissions::SUB_INSTANCES)) {
+        throw std::runtime_error("project has no sub-instances permission");
+    }
+    const auto& params = engine->getCoreParameters();
+    if (params.subProcessDepth >= MAX_SUBPROCESS_DEPTH) {
+        throw std::runtime_error("max subprocess depth exceeded");
+    }
+
     auto scriptPath = lua::require_lstring(L, 1);
-    io::path outputPath = "user:background.log"; // TODO:
+    io::path outputPath = lua::isstring(L, 2) ? lua::require_lstring(L, 2) : "";
     const auto& paths = engine->getPaths();
 
     std::vector<std::string> args {
-        // "--headless",
+        "--headless",
         "--res", paths.getResourcesFolder().u8string(),
         "--dir", paths.getUserFilesFolder().u8string(),
         "--script", io::resolve(scriptPath).u8string(),
+        "--sub-depth", std::to_string(engine->getCoreParameters()
+            .subProcessDepth + 1),
     };
     args.emplace_back("--project");
     args.emplace_back(io::resolve(engine->getProject().path).u8string());
diff --git a/src/main.cpp b/src/main.cpp
index 2438d5f50..83887422a 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -26,6 +26,8 @@ int main(int argc, char** argv) {
         if (!parse_cmdline(argc, argv, coreParameters)) {
             return EXIT_SUCCESS;
         }
+        logger.debug() << "sub-process depth: "
+                       << coreParameters.subProcessDepth;
     } catch (const std::runtime_error& err) {
         std::cerr << err.what() << std::endl;
         return EXIT_FAILURE;
diff --git a/src/util/command_line.cpp b/src/util/command_line.cpp
index 7f34bcea4..14f49caf4 100644
--- a/src/util/command_line.cpp
+++ b/src/util/command_line.cpp
@@ -78,12 +78,19 @@ static bool perform_keyword(
             params.debugServerString = reader.next();
             return true;
         }, "<serv>", "open debugging server where <serv> is {transport}:{port}"),
+        ArgC("--sub-depth", [&params, &reader]() -> bool {
+            params.subProcessDepth = reader.nextInt();
+            return true;
+        }, "<depth>", "sub-process depth"),
         ArgC("--help", []() -> bool {
             std::cout << "VoxelCore v" << ENGINE_VERSION_STRING << "\n\n";
             std::cout << "Command-line arguments:\n";
-            for (auto& a : argumentsCommandline) {
-                std::cout << std::setw(24) << std::left << (a.keyword + " " + a.args);
-                std::cout << "- " << a.help << std::endl;
+            for (auto& arg : argumentsCommandline) {
+                if (arg.help.empty()) {
+                    continue;
+                }
+                std::cout << std::setw(24) << std::left << (arg.keyword + " " + arg.args);
+                std::cout << "- " << arg.help << std::endl;
             }
             std::cout << std::endl;
             return false;