diff --git a/szutil_usagesurvey/init.lua b/szutil_usagesurvey/init.lua
index 632f26d..349b104 100644
--- a/szutil_usagesurvey/init.lua
+++ b/szutil_usagesurvey/init.lua
@@ -1,8 +1,10 @@
 -- LUALOCALS < ---------------------------------------------------------
-local io, ipairs, math, minetest, pairs, table, type
-    = io, ipairs, math, minetest, pairs, table, type
-local io_open, math_floor, table_concat, table_sort
-    = io.open, math.floor, table.concat, table.sort
+local io, ipairs, math, minetest, pairs, string, table, type
+    = io, ipairs, math, minetest, pairs, string, table, type
+local io_open, math_floor, string_gsub, string_match, table_concat,
+      table_sort
+    = io.open, math.floor, string.gsub, string.match, table.concat,
+      table.sort
 -- LUALOCALS > ---------------------------------------------------------
 
 local modname = minetest.get_current_modname()
@@ -136,13 +138,13 @@ local function deepadd(t, u)
 	return t
 end
 
+local dbnamepattern = "^blk.*%.json$"
 local function dbpath(id)
 	local p = minetest.get_worldpath() .. "/" .. modname
 	if id then
 		id = "" .. id
-
 		if id:sub(1, 3) ~= "blk" then
-			id = "blk" .. id .. ".txt"
+			id = "blk" .. id .. ".json"
 		end
 		p = p .. "/" .. id
 	end
@@ -152,9 +154,9 @@ end
 local function dbload(id)
 	local f = io_open(dbpath(id))
 	if not f then return {} end
-	local u = minetest.deserialize(f:read("*all"))
+	local s = f:read("*all")
 	f:close()
-	return u
+	return s and minetest.parse_json(s)
 end
 
 local lasttime = minetest.get_us_time() / 1000000
@@ -169,7 +171,7 @@ local function dbflush(forcerpt)
 	minetest.mkdir(dbpath())
 	for id, t in pairs(db) do
 		t = deepadd(dbload(id), t)
-		minetest.safe_file_write(dbpath(id), minetest.serialize(t))
+		minetest.safe_file_write(dbpath(id), minetest.write_json(t))
 		savedqty = savedqty + 1
 	end
 	db = {}
@@ -268,7 +270,9 @@ minetest.register_chatcommand("worlduse", {
 				t = deepadd(t, v)
 			end
 			for _, v in ipairs(minetest.get_dir_list(dbpath(), false)) do
-				t = deepadd(t, dbload(v))
+				if string_match(v, dbnamepattern) then
+					t = deepadd(t, dbload(v))
+				end
 			end
 
 			minetest.chat_send_player(name, fmtrpt(t))
@@ -276,3 +280,50 @@ minetest.register_chatcommand("worlduse", {
 	})
 
 ------------------------------------------------------------------------
+-- DATABASE MIGRATION
+
+do
+	local started = minetest.get_us_time()
+
+	local clean = 0
+	local dirty = 0
+	local fail = 0
+
+	local dirlist = minetest.get_dir_list(dbpath(), false)
+	local exists = {}
+	for _, v in ipairs(dirlist) do exists[v] = true end
+	for _, v in ipairs(dirlist) do
+		if string_match(v, "^blk.*%.txt$") then
+			local jv = string_gsub(v, "%.txt$", ".json")
+			if exists[jv] then
+				clean = clean + 1
+			else
+				local f = io_open(dbpath(v))
+				if not f then
+					fail = fail + 1
+				else
+					local s = f:read("*all")
+					f:close()
+					local u = minetest.deserialize(s)
+					if not u then
+						fail = fail + 1
+					else
+						minetest.safe_file_write(dbpath(jv),
+							minetest.write_json(u))
+						dirty = dirty + 1
+					end
+				end
+			end
+		end
+	end
+	local ms = math_floor((minetest.get_us_time() - started) / 1000)
+	if clean + dirty + fail == 0 then
+		minetest.log("action", modname .. ": db checked in " .. ms .. "ms")
+	else
+		minetest.log("action", modname .. ": db converted " .. dirty
+			.. ", " .. fail .. " failed, " .. clean .. " skipped in "
+			.. ms .. "ms")
+	end
+end
+
+------------------------------------------------------------------------