diff --git a/design.txt b/design.txt
index bc9fafd..281bb39 100644
--- a/design.txt
+++ b/design.txt
@@ -76,6 +76,20 @@ Example:
   stuff ?r
   extension:ecs2
 
+Extension structure
+-------------------
+extension
+`-- init.lua  << Loaded when the module is required
+
+Extension behavior
+------------------
+Extensions use the new Lua 5.1/5.2 module interface.
+
+If an extension wish to provide an interface to sandboxed code, it should
+implement function unsafe(), which returns the safe interface.
+
+Extensions and modules use require "buildat/extension/<name>" to use extensions.
+
 Network protocol
 ----------------
 (Type, length, data) tuples on TCP. In the future TLS can be taken into use. A
diff --git a/share/client/init.lua b/share/client/init.lua
index a4c64a3..b9e8639 100644
--- a/share/client/init.lua
+++ b/share/client/init.lua
@@ -11,58 +11,11 @@ function buildat:Logger(module)
 	return logger
 end
 
-local log = buildat:Logger("__client")
+local log = buildat:Logger("__client/init")
 
 log:info("init.lua loaded")
 
-require "Polycode/Core"
-scene = Scene(Scene.SCENE_2D)
-scene:getActiveCamera():setOrthoSize(640, 480)
-label = SceneLabel("Hello from Lua!", 32)
-label:setPosition(-50, -50, 0)
-scene:addChild(label)
+dofile(__buildat_get_path("share").."/client/test.lua")
+dofile(__buildat_get_path("share").."/client/packet.lua")
+dofile(__buildat_get_path("share").."/client/sandbox.lua")
 
-buildat.packet_subs = {}
-
-function buildat:sub_packet(name, cb)
-	buildat.packet_subs[name] = cb
-end
-function buildat:unsub_packet(cb)
-	for name, cb1 in pairs(buildat.packet_subs) do
-		if cb1 == cb then
-			buildat.packet_subs[cb] = nil
-		end
-	end
-end
-
-function buildat:send_packet(name, data)
-	__buildat_send_packet(name, data)
-end
-
-local sandbox_env = {
-	buildat = buildat,
-}
-
-local function run_in_sandbox(untrusted_code)
-	if untrusted_code:byte(1) == 27 then return nil, "binary bytecode prohibited" end
-	local untrusted_function, message = loadstring(untrusted_code)
-	if not untrusted_function then return nil, message end
-	setfenv(untrusted_function, sandbox_env)
-	return pcall(untrusted_function)
-end
-
-function buildat:run_script_file(name)
-	local code = __buildat_get_file_content(name)
-	if not code then
-		log:error("Failed to load script file: "+name)
-		return false
-	end
-	log:info("buildat:run_script_file("..name.."): #code="..#code)
-	local status, err = run_in_sandbox(code)
-	--local status, err = run_in_sandbox([[buildat:Logger("foo"):info("Pihvi")]])
-	if status == false then
-		log:error("Failed to run script: "..err)
-		return false
-	end
-	return true
-end
diff --git a/share/client/packet.lua b/share/client/packet.lua
new file mode 100644
index 0000000..91aa502
--- /dev/null
+++ b/share/client/packet.lua
@@ -0,0 +1,18 @@
+local log = buildat:Logger("__client/packet")
+
+__buildat_packet_subs = {}
+
+function buildat:sub_packet(name, cb)
+	__buildat_packet_subs[name] = cb
+end
+function buildat:unsub_packet(cb)
+	for name, cb1 in pairs(buildat.packet_subs) do
+		if cb1 == cb then
+			__buildat_packet_subs[cb] = nil
+		end
+	end
+end
+
+function buildat:send_packet(name, data)
+	__buildat_send_packet(name, data)
+end
diff --git a/share/client/sandbox.lua b/share/client/sandbox.lua
new file mode 100644
index 0000000..22f7c3c
--- /dev/null
+++ b/share/client/sandbox.lua
@@ -0,0 +1,34 @@
+local log = buildat:Logger("__client/sandbox")
+
+local sandbox = {}
+
+sandbox.buildat = buildat
+
+sandbox.require = function(name)
+	error("require: \""..name.."\" not found in sandbox")
+end
+
+local function run_in_sandbox(untrusted_code, sandbox)
+	if untrusted_code:byte(1) == 27 then return nil, "binary bytecode prohibited" end
+	local untrusted_function, message = loadstring(untrusted_code)
+	if not untrusted_function then return nil, message end
+	setfenv(untrusted_function, sandbox)
+	return pcall(untrusted_function)
+end
+
+function buildat:run_script_file(name)
+	local code = __buildat_get_file_content(name)
+	if not code then
+		log:error("Failed to load script file: "+name)
+		return false
+	end
+	log:info("buildat:run_script_file("..name.."): #code="..#code)
+	local status, err = run_in_sandbox(code, sandbox)
+	--local status, err = run_in_sandbox(
+	--		[[buildat:Logger("foo"):info("Pihvi")]], sandbox)
+	if status == false then
+		log:error("Failed to run script: "..err)
+		return false
+	end
+	return true
+end
diff --git a/share/client/test.lua b/share/client/test.lua
new file mode 100644
index 0000000..7a43771
--- /dev/null
+++ b/share/client/test.lua
@@ -0,0 +1,11 @@
+local log = buildat:Logger("__client/test")
+
+--[[
+require "Polycode/Core"
+scene = Scene(Scene.SCENE_2D)
+scene:getActiveCamera():setOrthoSize(640, 480)
+label = SceneLabel("Hello from Lua!", 32)
+label:setPosition(-50, -50, 0)
+scene:addChild(label)
+]]
+
diff --git a/src/client/app.cpp b/src/client/app.cpp
index f79b202..6788218 100644
--- a/src/client/app.cpp
+++ b/src/client/app.cpp
@@ -278,6 +278,7 @@ struct CApp: public Polycode::EventHandler, public App
 }
 		DEF_BUILDAT_FUNC(send_packet);
 		DEF_BUILDAT_FUNC(get_file_content)
+		DEF_BUILDAT_FUNC(get_path)
 
 		ss_ init_lua_path = g_client_config.share_path+"/client/init.lua";
 		int error = luaL_dofile(L, init_lua_path.c_str());
@@ -369,6 +370,22 @@ struct CApp: public Polycode::EventHandler, public App
 			return 0;
 		}
 	}
+
+	// get_path(name: string)
+	static int l_get_path(lua_State *L)
+	{
+		size_t name_len = 0;
+		const char *name_c = lua_tolstring(L, 1, &name_len);
+		ss_ name(name_c, name_len);
+
+		if(name == "share"){
+			ss_ path = g_client_config.share_path;
+			lua_pushlstring(L, path.c_str(), path.size());
+			return 1;
+		}
+		log_w(MODULE, "Unknown named path: \"%s\"", cs(name));
+		return 0;
+	}
 };
 
 App* createApp(Polycode::PolycodeView *view)