diff --git a/userspace/digwatch/lua/rule_loader.lua b/userspace/digwatch/lua/rule_loader.lua
index 284c1be0..f1132d87 100644
--- a/userspace/digwatch/lua/rule_loader.lua
+++ b/userspace/digwatch/lua/rule_loader.lua
@@ -56,7 +56,7 @@ local state
    to the line-oriented compiler.
 --]]
 local function init()
-   return {macros={}, filter_ast=nil}
+   return {macros={}, filter_ast=nil, n_rules=0}
 end
 
 
@@ -66,12 +66,17 @@ function load_rule(r)
    end
    local line_ast = compiler.compile_line(r, state.macros)
 
-   if (line_ast.type == "MacroDef") then
+   if (line_ast.type == nil) then -- blank line
+      return
+   elseif (line_ast.type == "MacroDef") then
       return
    elseif (not (line_ast.type == "Rule")) then
       error ("Unexpected type in load_rule: "..line_ast.type)
    end
 
+   digwatch.set_formatter(state.n_rules, line_ast.output.value)
+   state.n_rules = state.n_rules + 1
+
    if (state.filter_ast == nil) then
       state.filter_ast = line_ast.filter.value
    else
diff --git a/userspace/digwatch/rules.cpp b/userspace/digwatch/rules.cpp
index d8c3ecac..39f883ce 100644
--- a/userspace/digwatch/rules.cpp
+++ b/userspace/digwatch/rules.cpp
@@ -6,18 +6,57 @@ extern "C" {
 #include "lauxlib.h"
 }
 
+std::map<uint32_t, sinsp_evt_formatter*> g_format_map;
+sinsp* g_inspector;
+
+const static struct luaL_reg ll_digwatch [] =
+{
+	{"set_formatter", &digwatch_rules::set_formatter},
+	{NULL,NULL}
+};
+
 digwatch_rules::digwatch_rules(sinsp* inspector, string lua_main_filename, string lua_dir)
 {
+	g_inspector = inspector;
+
 	// Initialize Lua interpreter
 	m_ls = lua_open();
 	luaL_openlibs(m_ls);
 
 	m_lua_parser = new lua_parser(inspector, m_ls);
 
+	luaL_openlib(m_ls, "digwatch", ll_digwatch, 0);
+
 	add_lua_path(lua_dir);
 	load_compiler(lua_main_filename);
 }
 
+int digwatch_rules::set_formatter (lua_State *ls) {
+	uint32_t index = luaL_checkinteger(ls, 1);
+	string format = luaL_checkstring(ls, 2);
+
+	try
+	{
+		if(format == "" || format == "default")
+		{
+			g_format_map[index] = new sinsp_evt_formatter(g_inspector, DEFAULT_OUTPUT_STR);
+		}
+		else
+		{
+			g_format_map[index] = new sinsp_evt_formatter(g_inspector, format);
+		}
+	}
+	catch(sinsp_exception& e)
+	{
+		string err = "invalid output format " + format;
+		fprintf(stderr, "%s\n", err.c_str());
+		throw sinsp_exception("set_formatter error");
+	}
+
+	return 0;
+}
+
+
 void digwatch_rules::add_lua_path(string path)
 {
 	path += "?.lua";
@@ -84,7 +123,7 @@ void digwatch_rules::load_rules(string rules_filename)
 		if(lua_pcall(m_ls, 1, 0, 0) != 0)
 		{
 			const char* lerr = lua_tostring(m_ls, -1);
-			string err = "Error loading rule: " + string(lerr);
+			string err = "Error loading rule '" + line + "':" + string(lerr);
 			throw sinsp_exception(err);
 		}
 	}
diff --git a/userspace/digwatch/rules.h b/userspace/digwatch/rules.h
index c46ea97f..7f007152 100644
--- a/userspace/digwatch/rules.h
+++ b/userspace/digwatch/rules.h
@@ -3,6 +3,8 @@
 #include "sinsp.h"
 #include "lua_parser.h"
 
+class sinsp_evt_formatter;
+
 class digwatch_rules
 {
  public:
@@ -11,12 +13,16 @@ class digwatch_rules
 	void load_rules(string rules_filename);
 	sinsp_filter* get_filter();
 
+	// set_formatter(index, format_string)
+	static int set_formatter(lua_State *ls);
  private:
 	void add_lua_path(string path);
 	void load_compiler(string lua_main_filename);
 
 	lua_parser* m_lua_parser;
 	lua_State* m_ls;
+
 	string m_lua_load_rule = "load_rule";
 	string m_lua_on_done = "on_done";
+	string m_lua_on_event = "on_event";
 };