diff --git a/.github/workflows/mineunit.yml b/.github/workflows/mineunit.yml
index 8a55758..d1970fc 100644
--- a/.github/workflows/mineunit.yml
+++ b/.github/workflows/mineunit.yml
@@ -1,7 +1,7 @@
 
 name: mineunit
 
-on: [push, pull_request]
+on: [push, pull_request, workflow_dispatch]
 
 jobs:
   build:
diff --git a/init.lua b/init.lua
index 28a6915..fabadbd 100644
--- a/init.lua
+++ b/init.lua
@@ -26,7 +26,7 @@ local default_config = {
 	engine_version = "mineunit",
 }
 
-for k,v in pairs(mineunit_conf_defaults) do
+for k,v in pairs(mineunit_conf_defaults or {}) do
 	default_config[k] = v
 end
 
diff --git a/itemstack.lua b/itemstack.lua
index fc03071..8026b25 100644
--- a/itemstack.lua
+++ b/itemstack.lua
@@ -11,7 +11,7 @@ function ItemStack:set_name(item_name)
 	assert.is_string(item_name, "ItemStack:set_name expected item_name to be string")
 	self._name = item_name
 	if item_name == "" then
-		self:set_count(0)
+		self:clear()
 		return true
 	end
 	return false
@@ -20,15 +20,27 @@ end
 function ItemStack:get_count() return self._count end
 --* `set_count(count)`: returns a boolean indicating whether the item was cleared
 --    `count`: number, unsigned 16 bit integer
-function ItemStack:set_count(count) self._count = count end
+function ItemStack:set_count(count)
+	if count > 0 and count <= 65535 then
+		self._count = count
+		return true
+	else
+		self:clear()
+		return false
+	end
+end
 --* `get_wear()`: returns tool wear (`0`-`65535`), `0` for non-tools.
 function ItemStack:get_wear() return self._wear end
 --* `set_wear(wear)`: returns boolean indicating whether item was cleared
 --    `wear`: number, unsigned 16 bit integer
 function ItemStack:set_wear(wear)
-	assert(wear <= 65535, "ItemStack:set_wear invalid wear value: "..tostring(wear))
-	wear = wear < 0 and -((-wear) % 65536) or wear
-	self._wear = math.max(0, wear < 0 and 65536 + wear or wear)
+	if wear <= 65535 then
+		self._wear = wear % 65536
+		return true
+	else
+		self.clear()
+		return false
+	end
 end
 --* `get_meta()`: returns ItemStackMetaRef. See section for more details
 function ItemStack:get_meta() return self._meta end
@@ -63,7 +75,15 @@ function ItemStack:get_short_description()
 	if value then return value:gmatch("[^\r\n]+")() end
 end
 --* `clear()`: removes all items from the stack, making it empty.
-function ItemStack:clear() self._count = 0 end
+-- https://github.com/minetest/minetest/blob/0f25fa7af655b98fa401176a523f269c843d1943/src/inventory.h#L63-L69
+-- https://github.com/minetest/minetest/blob/0f25fa7af655b98fa401176a523f269c843d1943/src/script/lua_api/l_item.cpp#L206-L214
+function ItemStack:clear()
+	self._name = ""
+	self._count = 0
+	self._wear = 0
+	self._meta:_clear()
+	return true
+end
 --* `replace(item)`: replace the contents of this stack.
 --    `item` can also be an itemstring or table.
 function ItemStack:replace(item)
@@ -76,12 +96,25 @@ end
 --* `to_string()`: returns the stack in itemstring form.
 -- https://github.com/minetest/minetest/blob/5.4.0/src/inventory.cpp#L59-L85
 function ItemStack:to_string()
-	-- FIXME: Does not currently serialize metadata
-	return ("%s %d %d"):format(
-		self:get_name(),
-		self:get_count(),
-		self:get_wear()
-	)
+	local name = self:get_name()
+	local count = self:get_count()
+	local wear = self:get_wear()
+	if name == "" or count == 0 then
+		return ""
+	else
+		local parts = {name}
+		if count > 1 or wear ~= 0 or not self._meta:_empty() then
+			table.insert(parts, tostring(count))
+		end
+		if wear ~= 0 or not self._meta:_empty() then
+			table.insert(parts, tostring(wear))
+		end
+		if not self._meta:_empty() then
+			table.insert(parts, self._meta:_serialize())
+		end
+
+		return table.concat(parts, " ")
+	end
 end
 --* `to_table()`: returns the stack in Lua table form.
 function ItemStack:to_table()
@@ -135,6 +168,14 @@ function ItemStack:add_item(item)
 		return leftover
 	end
 
+	if self:get_name() ~= leftover:get_name() then
+		return leftover
+	end
+
+	if self._meta ~= leftover._meta then
+		return leftover
+	end
+
 	local stack_max = item:get_stack_max()
 	local count = self:get_count()
 	local space = stack_max - count
@@ -156,7 +197,7 @@ function ItemStack:item_fits(item)
 		return true
 	end
 	local stack = ItemStack(item)
-	if self:get_name() == stack:get_name() then
+	if self:get_name() == stack:get_name() and self._meta == item._meta then
 		return self:get_free_space() >= stack:get_count()
 	end
 	return false
@@ -165,11 +206,11 @@ end
 --    Take (and remove) up to `n` items from this stack
 --    `n`: number, default: `1`
 function ItemStack:take_item(n)
+	local taken = ItemStack(self)
 	n = math.min(self:get_count(), n or 1)
 	self:set_count(self:get_count() - n)
-	local stack = ItemStack(self)
-	stack:set_count(n)
-	return stack
+	taken:set_count(n)
+	return taken
 end
 --* `peek_item(n)`: returns taken `ItemStack`
 --    Copy (don't remove) up to `n` items from this stack
@@ -183,8 +224,7 @@ function ItemStack:peek_item(n)
 end
 
 function ItemStack:__tostring()
-	local count = self:get_count()
-	return 'ItemStack("' .. self:get_name() .. (count > 1 and " "..count or "") .. '")'
+	return 'ItemStack("' .. self:to_string() .. '")'
 end
 
 -- TODO: Allows `same` assertions but in corner cases makes mod code to return true where engine would return false.
diff --git a/metadata.lua b/metadata.lua
index 03966fb..d05a889 100644
--- a/metadata.lua
+++ b/metadata.lua
@@ -1,5 +1,6 @@
 
 mineunit("common/misc_helpers")
+local json = require('mineunit.lib.json')
 
 local function assert_invlist_index(index, size)
 	assert(type(index) == "number" and math.floor(index) == index, "InvList:set_stack: Invalid InvList stack index")
@@ -304,7 +305,9 @@ function MetaDataRef:from_table(t)
 		self._data = table.copy(t.fields)
 	end
 end
-function MetaDataRef:equals(other) error("NOT IMPLEMENTED") end
+function MetaDataRef:equals(other)
+	return self:__eq(other)
+end
 
 -- TODO: Allows `same` assertions but in corner cases makes mod code to return true where engine would return false.
 -- Requires either overriding luassert `same` (nice for users) or only allowing special assertions (not so nice).
@@ -322,6 +325,86 @@ function MetaDataRef:__eq(other)
 	return false
 end
 
+function MetaDataRef:_empty()
+	for _ in pairs(self._data) do
+		return false
+	end
+	return true
+end
+
+function MetaDataRef:_clear()
+	for key in pairs(self._data) do
+		self._data[key] = nil
+	end
+end
+
+--[[
+	serialize metadata, for use in itemstrings
+	https://github.com/minetest/minetest/blob/0f25fa7af655b98fa401176a523f269c843d1943/src/itemstackmetadata.cpp#L61-L71
+]]
+local DESERIALIZE_START = "\01"
+local DESERIALIZE_KV_DELIM = "\02"
+local DESERIALIZE_PAIR_DELIM = "\03"
+function MetaDataRef:_serialize()
+	local parts = {}
+	table.insert(parts, DESERIALIZE_START)
+	for k, v in pairs(self._data) do
+		if k ~= "" or v ~= "" then
+			table.insert(parts, k)
+			table.insert(parts, DESERIALIZE_KV_DELIM)
+			table.insert(parts, v)
+			table.insert(parts, DESERIALIZE_PAIR_DELIM)
+		end
+	end
+
+	return json.encode(table.concat(parts, ""))
+end
+
+--[[
+	deserialize metadata, for use in itemstrings
+	https://github.com/minetest/minetest/blob/0f25fa7af655b98fa401176a523f269c843d1943/src/itemstackmetadata.cpp#L73-L94
+]]
+function MetaDataRef:_deserialize(s)
+	local ds = json.decode(s)
+	self:_clear()
+
+	local function find_next(i)
+		if i > #ds then
+			return
+		end
+		local key_start = i
+		while ds:sub(i, i) ~= DESERIALIZE_KV_DELIM and i <= #ds do
+			i = i + 1
+		end
+		local key_end = i - 1
+		i = i + 1
+		local value_start = i
+		while ds:sub(i, i) ~= DESERIALIZE_PAIR_DELIM and i <= #ds do
+			i = i + 1
+		end
+		local value_end = i - 1
+		i = i + 1
+		return i, ds:sub(key_start, key_end), ds:sub(value_start, value_end)
+	end
+
+	if ds:sub(1, 1) == DESERIALIZE_START then
+		local key, value
+		local i = 2
+		while true do
+			i, key, value = find_next(i)
+			if i and key and value then
+				self._data[key] = value
+			else
+				break
+			end
+		end
+	else
+		error(("error deserializing %q (%q)"):format(s, ds))
+		-- "BACKWARDS COMPATIBILITY"
+		self._data[""] = s
+	end
+end
+
 mineunit.export_object(MetaDataRef, {
 	name = "MetaDataRef",
 	constructor = function(self, value)
@@ -330,6 +413,10 @@ mineunit.export_object(MetaDataRef, {
 			obj = {}
 		elseif mineunit.utils.type(value) == "MetaDataRef" then
 			obj = table.copy(value)
+		elseif type(value) == "string" then
+			local it = MetaDataRef()
+			it:_deserialize(value)
+			return it
 		else
 			print(value)
 			error("TYPE NOT IMPLEMENTED: " .. type(value))
diff --git a/player.lua b/player.lua
index 961021b..3a7a8de 100644
--- a/player.lua
+++ b/player.lua
@@ -228,7 +228,12 @@ local function swap_stack(toinv, tolist, toindex, frominv, fromlist, fromindex,
 	end
 
 	-- Place source stack into target inventory
-	local placedstack = count ~= -1 and stack:take_item(count) or ItemStack(stack)
+	local placedstack
+	if count == -1 then
+		placedstack = ItemStack(stack)
+	else
+		placedstack = stack:take_item(count)
+	end
 	toinv:set_stack(tolist, toindex, placedstack)
 
 	-- Return leftovers to source inventory
diff --git a/spec/itemstack_spec.lua b/spec/itemstack_spec.lua
index 111cf0f..445f360 100644
--- a/spec/itemstack_spec.lua
+++ b/spec/itemstack_spec.lua
@@ -178,4 +178,50 @@ describe("ItemStack", function()
 
 	end)
 
+	describe("stack metadata", function()
+
+		it("metadata serializes in itemstring", function()
+			local stack = ItemStack("test")
+			local stack_meta = stack:get_meta()
+			stack_meta:set_int("foo", 1)
+			assert.equals("test 1 0 \"\\u0001foo\\u00021\\u0003\"", stack:to_string())
+		end)
+
+		it("metadata properly initialized by itemstring", function()
+			local stack = ItemStack("test 1 0 \"\\u0001foo\\u00021\\u0003\"")
+			local stack_meta = stack:get_meta()
+			assert.equals("", stack_meta:get_string(""))
+			assert.equals(1, stack_meta:get_int("foo"))
+		end)
+
+		it("allow stacking matched metadata", function()
+			local stack1 = ItemStack("test 1 0 \"\\u0001foo\\u00021\\u0003\"")
+			local stack2 = ItemStack("test 1 0 \"\\u0001foo\\u00021\\u0003\"")
+
+			assert.is_true(stack1:item_fits(stack2))
+
+			local remainder = stack1:add_item(stack2)
+
+			assert.is_true(remainder:is_empty())
+			assert.equals(2, stack1:get_count())
+			local meta = stack1:get_meta()
+			assert.equals(1, meta:get_int("foo"))
+		end)
+
+		it("disallow stacking mismatched metadata", function()
+			local stack1 = ItemStack("test 1 0 \"\\u0001foo\\u00021\\u0003\"")
+			local stack2 = ItemStack("test 1 0 \"\\u0001foo\\u00022\\u0003\"")
+
+			assert.is_false(stack1:item_fits(stack2))
+
+			local remainder = stack1:add_item(stack2)
+
+			assert.equals("test 1 0 \"\\u0001foo\\u00022\\u0003\"", remainder:to_string())
+			assert.equals(1, stack1:get_count())
+			local meta = remainder:get_meta()
+			assert.equals(2, meta:get_int("foo"))
+		end)
+
+	end)
+
 end)
diff --git a/spec/player_spec.lua b/spec/player_spec.lua
index 929c81b..3cbc4db 100644
--- a/spec/player_spec.lua
+++ b/spec/player_spec.lua
@@ -377,7 +377,8 @@ describe("Mineunit Player", function()
 		end)
 
 		it("works without source index", function()
-			SX:do_metadata_inventory_put({x=0,y=1,z=0}, "chest", 1)
+			local can_put_count = SX:do_metadata_inventory_put({x=0,y=1,z=0}, "chest", 1)
+			assert.same(can_put_count, 33)
 			local expected = InvRef()
 			expected:set_size("chest", 3)
 			expected:set_stack("chest", 1, ItemStack("stone 33"))
@@ -386,7 +387,8 @@ describe("Mineunit Player", function()
 		end)
 
 		it("works with source index", function()
-			SX:do_metadata_inventory_put({x=0,y=1,z=0}, "chest", 2, 2)
+			local can_put_count = SX:do_metadata_inventory_put({x=0,y=1,z=0}, "chest", 2, 2)
+			assert.same(can_put_count, 42)
 			local expected = InvRef()
 			expected:set_size("chest", 3)
 			expected:set_stack("chest", 1, ItemStack("stone 33"))
@@ -396,7 +398,8 @@ describe("Mineunit Player", function()
 		end)
 
 		it("works with ItemStack", function()
-			SX:do_metadata_inventory_put({x=0,y=1,z=0}, "chest", 3, ItemStack("stone 96"))
+			local can_put_count = SX:do_metadata_inventory_put({x=0,y=1,z=0}, "chest", 3, ItemStack("stone 96"))
+			assert.same(can_put_count, 96)
 			local expected = InvRef()
 			expected:set_size("chest", 3)
 			expected:set_stack("chest", 1, ItemStack("stone 33"))