diff --git a/worldeditadditions_core/register/check.lua b/worldeditadditions_core/register/check.lua
index 1dfb87b..5c08285 100644
--- a/worldeditadditions_core/register/check.lua
+++ b/worldeditadditions_core/register/check.lua
@@ -1,14 +1,26 @@
-function worldeditadditions_core.register_command(def)
-	local def = table.copy(def)
-	assert(name and #name > 0)
-	assert(def.privs)
-	def.require_pos = def.require_pos or 0
-	assert(def.require_pos >= 0 and def.require_pos < 3)
-	if def.params == "" and not def.parse then
-		def.parse = function(params_text) return true end
-	else
-		assert(def.parse)
+function worldeditadditions_core.check_command(name, def)
+	if not (name and #name > 0) then
+		return false, "Error: No command name."
 	end
-	assert(def.nodes_needed == nil or type(def.nodes_needed) == "function")
-	assert(def.func)
+	if not def.privs then
+		return false, "Error: privs is nill. Expected table."
+	end
+	def.require_pos = def.require_pos or 0
+	if not (def.require_pos >= 0 and def.require_pos < 3) then
+		return false, "Error: require_pos must be greater than -1 and less than 3."
+	end
+	if not def.parse then
+		if def.params == "" then
+			def.parse = function(params_text) return true end
+		else
+			return false, "Error: parse function is invalid."
+		end
+	end
+	if not (def.nodes_needed == nil or type(def.nodes_needed) == "function") then
+		return false, "Error: nodes_needed must be nil or function."
+	end
+	if not def.func then
+		return false, "Error: main function is invalid."
+	end
+	return true
 end