diff --git a/.luacheckrc b/.luacheckrc
new file mode 100644
index 0000000..2d38621
--- /dev/null
+++ b/.luacheckrc
@@ -0,0 +1,16 @@
+globals = {
+	"epidermis",
+	minetest = {
+		"dynamic_add_media" -- overridden
+	}
+}
+
+read_globals = {
+	-- Minetest
+    "minetest",
+    "ItemStack",
+    "vector",
+	-- Mods
+	"modlib",
+	"moblib"
+}
\ No newline at end of file
diff --git a/colorpicker_rgb_formspec.lua b/colorpicker_rgb_formspec.lua
index 5656b52..e6d72ab 100644
--- a/colorpicker_rgb_formspec.lua
+++ b/colorpicker_rgb_formspec.lua
@@ -1,7 +1,8 @@
 local function get_gradient_texture(component, color)
 	local old_value = color[component]
 	color[component] = 255
-	local texture = ("epxw.png^[multiply:%s^[resize:256x1^[mask:epidermis_gradient_%s.png"):format(color:to_string(), component)
+	local texture = ("epxw.png^[multiply:%s^[resize:256x1^[mask:epidermis_gradient_%s.png")
+		:format(color:to_string(), component)
 	color[component] = old_value
 	return texture
 end
@@ -27,7 +28,8 @@ function epidermis.show_colorpicker_formspec(player, color, callback)
 			local component_short = component:sub(1, 1):lower()
 			local y = 0.25 + index * 1.25
 			table.insert(fs, ("scrollbar[0.25,%f;8,0.5;horizontal;%s;%d]"):format(y, component_short, color[component_short]))
-			table.insert(fs, ("label[0.25,%f;%s]"):format(y + 0.75, minetest.colorize(("#%06X"):format(0xFF * 0x100 ^ (3 - index)), component:sub(1, 1))))
+			table.insert(fs, ("label[0.25,%f;%s]")
+				:format(y + 0.75, minetest.colorize(("#%06X"):format(0xFF * 0x100 ^ (3 - index)), component:sub(1, 1))))
 			table.insert(fs, ("image[0.75,%f;6.5,0.5;%s]"):format(y + 0.5, get_gradient_texture(component_short, color)))
 			table.insert(fs, ("field[7.25,%f;1,0.5;field_%s;;%s]"):format(y + 0.5, component_short, color[component_short]))
 			table.insert(fs, ("field_close_on_enter[field_%s;false]"):format(component_short))
diff --git a/dynamic_add_media.lua b/dynamic_add_media.lua
index 725b975..035b8ac 100644
--- a/dynamic_add_media.lua
+++ b/dynamic_add_media.lua
@@ -1,5 +1,7 @@
 local media_paths = epidermis.media_paths
--- TODO keep count of total added media, force-kick players after their RAM is too full, restart after server disk is too full
+-- TODO keep count of total added media:
+-- Force-kick players after their RAM is too full
+-- Restart after server disk is too full
 function epidermis.dynamic_add_media(path, on_all_received, ephemeral)
 	local filename = modlib.file.get_name(path)
 	local existing_path = media_paths[filename]
@@ -26,7 +28,8 @@ function epidermis.dynamic_add_media(path, on_all_received, ephemeral)
 	for player in modlib.minetest.connected_players() do
 		local name = player:get_player_name()
 		if minetest.get_player_information(name).protocol_version < 39 then
-			minetest.kick_player(name, "Your Minetest client is outdated (< 5.3) and can't receive dynamic media. Rejoin to get the added media.")
+			minetest.kick_player(name,
+				"Your Minetest client is outdated (< 5.3) and can't receive dynamic media. Rejoin to get the added media.")
 		else
 			to_receive[name] = true
 		end
diff --git a/formspec.lua b/formspec.lua
index c553d2e..8e3f163 100644
--- a/formspec.lua
+++ b/formspec.lua
@@ -27,7 +27,6 @@ function epidermis.show_formspec(player, formspec, handler)
 	}
 	id = id + 1
 	if id > 2^50 then id = 1 end
-	-- See https://github.com/minetest/minetest/issues/11907: Formspecs must not use exit buttons if there are to be following stages
 	minetest.show_formspec(player_name, formspec_name, formspec)
 end
 
diff --git a/help.lua b/help.lua
index acee05f..e5db902 100644
--- a/help.lua
+++ b/help.lua
@@ -45,7 +45,13 @@ local help = {
 		"Epidermis Spawner",
 		"Spawns a paintable epidermis that copies your skin. Use your bare hands on the paintable:",
 		"- Left-click (punch) to swap skins",
-		"- Right-click (interact) to open the control panel, which allows toggling backface culling, changing rotation, previewing the texture, playing the animation, picking a texture from and uploading to SkinDB"
+		"- Right-click (interact) to open the control panel, which allows " .. table.concat({
+			"toggling backface culling",
+			"changing rotation",
+			"previewing the texture",
+			"playing the animation",
+			"picking a texture from and uploading to SkinDB"
+		}, ", ") .. "."
 	),
 	item_(
 		"epidermis:spawner_colorpicker",
@@ -56,19 +62,23 @@ local help = {
 	item_(
 		"epidermis:undo_redo",
 		"Undo / redo",
-		"Left-click to undo the last action, right-click to redo undone actions. Only a limited amount of actions can be undone / redone."
+		"Left-click to undo the last action, right-click to redo undone actions. "
+		.. "Only a limited amount of actions can be undone / redone."
 	),
 	item_(
 		"epidermis:eraser",
 		"Eraser",
-		"Left-click to mark a pixel as transparent, right-click to restore opacity of the first transparent pixel above the pointed pixel."
+		"Left-click to mark a pixel as transparent, "
+		.. "right-click to restore opacity of the first transparent pixel above the pointed pixel."
 	),
 	tags.b({
-		"The painting tools below support right-clicking an epidermis or HSV color picker to choose a color. If nothing is pointed, you will be shown a RGB color picker.",
+		"The painting tools below support right-clicking an epidermis or HSV color picker to choose a color. ",
+		"If nothing is pointed, you will be shown a RGB color picker.",
 	}),
 	"\n",
 	item_("epidermis:pen", "Pen", "Left-click to set a single pixel."),
-	item_("epidermis:filling_bucket", "Filling Bucket", "Left-click to fill pixels of (exactly) the same color on the texture."),
+	item_("epidermis:filling_bucket", "Filling Bucket",
+		"Left-click to fill pixels of (exactly) the same color on the texture."),
 	item_("epidermis:line", "Line", "Drag to draw a line. The line is drawn on the texture, not the model."),
 	item_(
 		"epidermis:rectangle",
diff --git a/paintable.lua b/paintable.lua
index fc154e1..78f1ae1 100644
--- a/paintable.lua
+++ b/paintable.lua
@@ -279,7 +279,8 @@ function def:on_activate()
 		local texture
 		path, texture = epidermis.get_last_epidermis_path(self._.id)
 		if path then
-			minetest.log("warning", ("Force-upgrading paintable #%d to texture %s due to staticdata loss"):format(self._.id, texture))
+			minetest.log("warning", ("Force-upgrading paintable #%d to texture %s due to staticdata loss")
+				:format(self._.id, texture))
 			self:_set_texture(texture, true) -- related staticdata must be overwritten, as it relates to the old texture
 		else
 			minetest.log("warning", ("No texture for paintable #%d available, defaulting to character.png."):format(self._.id))
@@ -312,7 +313,8 @@ function def:_get_intersection_infos(mt_pos, mt_direction)
 	local rotation_axis, rotation_angle = epidermis.vector_axis_angle(rotation)
 	-- Instead of transforming all triangle vertices, we inversely transform the ray, which is a lot cheaper
 	local inv_trans_dir = mlvec.rotate3((direction / scale):normalize(), rotation_axis, -rotation_angle)
-	local inv_trans_rel_pos = mlvec.rotate3(pos - mlvec.from_minetest(self.object:get_pos()), rotation_axis, -rotation_angle)
+	local inv_trans_rel_pos = mlvec.rotate3(pos - mlvec.from_minetest(self.object:get_pos()),
+		rotation_axis, -rotation_angle)
 
 	for texid, tris in pairs(assert(models[properties.mesh]).triangle_sets) do
 		for _, triangle in pairs(tris) do
@@ -537,7 +539,9 @@ function def:_show_upload_formspec(player, message)
 		local credit, completeness = context.credit, context.completeness
 		local name, author = modlib.text.trim_spacing(fields.name or ""), modlib.text.trim_spacing(fields.author or "")
 		if not (credit and completeness and name ~= "" and author ~= "") then
-			self:_show_upload_formspec(player, minetest.colorize(epidermis.colors.error:to_string(), "Please fill out the form!"))
+			self:_show_upload_formspec(player,
+				minetest.colorize(epidermis.colors.error:to_string(),
+				"Please fill out the form!"))
 			return
 		end
 		epidermis.close_formspec(player)
@@ -581,9 +585,9 @@ function def:_show_picker_formspec(player)
 		results = epidermis.skins,
 		index = #epidermis.skins
 	}
-	local function show_formspec()
+	local function get_formspec()
 		local skin = assert(context.results[context.index])
-		epidermis.show_formspec(player, table.concat{
+		return table.concat{
 			"size[8.5,5.25,false]",
 			"real_coordinates[true]",
 			"label[0.25,0.5;Pick a texture:]",
@@ -603,21 +607,26 @@ function def:_show_picker_formspec(player)
 			"label[3.5,1.75;Author: ", FSE(skin.author), "]";
 			"label[3.5,2.25;License: ", FSE(skin.license), "]";
 			"label[3.5,2.75;Uploaded: ", FSE(skin.uploaded), "]";
-			"label[3.5,3.25;", FSE(context.message or (skin.deleted and minetest.colorize(epidermis.colors.error:to_string(), "This skin was deleted!")) or ""), "]";
-			("hypertext[4.75,4.45;2,0.7;_of;<global valign=middle halign=right>%d/%d]"):format(context.index, #context.results), -- HACK
+			"label[3.5,3.25;", FSE(context.message
+				or (skin.deleted and minetest.colorize(epidermis.colors.error:to_string(), "This skin was deleted!")) or ""), "]";
+			("hypertext[4.75,4.45;2,0.7;_of;<global valign=middle halign=right>%d/%d]")
+				:format(context.index, #context.results), -- HACK
 			"image_button[6.75,4.5;0.5,0.5;", FSE(epidermis.textures.dice), ";random;]";
 			"tooltip[random;Random]",
 			"image_button[7.25,4.5;0.5,0.5;", FSE(epidermis.textures.previous), ";previous;]";
 			"tooltip[previous;Previous]",
 			"image_button[7.75,4.5;0.5,0.5;", FSE(epidermis.textures.next), ";next;]";
 			"tooltip[next;Next]",
-		}, function(fields)
+		}
+	end
+	local function show_formspec()
+		epidermis.show_formspec(player, get_formspec(), function(fields)
 			if fields.set then
-				local skin = context.results[context.index]
-				if skin.deleted then
+				local selected_skin = context.results[context.index]
+				if selected_skin.deleted then
 					epidermis.send_notification(player, "The selected skin was deleted!")
 				else
-					self:_set_texture(skin.texture, true)
+					self:_set_texture(selected_skin.texture, true)
 				end
 				return
 			end
diff --git a/tools.lua b/tools.lua
index ddcb7db..32d5d69 100644
--- a/tools.lua
+++ b/tools.lua
@@ -48,7 +48,9 @@ minetest.register_craftitem("epidermis:spawner_colorpicker", {
 		-- HACK assuming a node size of exactly one
 		local face_pos = vector.divide(vector.add(pointed_thing.above, pointed_thing.under), 2)
 		local direction = vector.direction(pointed_thing.under, pointed_thing.above)
-		local object = minetest.add_entity(vector.add(face_pos, vector.multiply(direction, colorpicker_thickness/2)), colorpicker_name)
+		local object = minetest.add_entity(
+			vector.add(face_pos, vector.multiply(direction, colorpicker_thickness/2)),
+			colorpicker_name)
 		if not object then
 			send_notification(user, "Can't spawn colorpicker!", "error")
 			return
@@ -68,7 +70,9 @@ local function set_item_color(itemstack, colorspec)
 		-- Bright background: Choose a dark foreground  color
 		foreground = "#000000"
 	end
-	itemstack:get_meta():set_string("description", minetest.get_background_escape_sequence(colorstring) .. minetest.colorize(foreground, itemstack:get_definition().description))
+	itemstack:get_meta():set_string("description",
+		minetest.get_background_escape_sequence(colorstring)
+		.. minetest.colorize(foreground, itemstack:get_definition().description))
 end
 
 local function get_entity(user, pointed_thing, allow_any)
@@ -181,7 +185,7 @@ end)
 minetest.register_tool("epidermis:eraser", {
 	description = "Eraser",
 	inventory_image = "epidermis_eraser.png",
-	on_secondary_use = function(_itemstack, user, pointed_thing)
+	on_secondary_use = function(_, user, pointed_thing)
 		local paintable = get_entity(user, pointed_thing)
 		if not paintable then
 			return
@@ -201,7 +205,7 @@ minetest.register_tool("epidermis:eraser", {
 			paintable:_update_texture()
 		end
 	end,
-	on_use = function(_itemstack, user, pointed_thing)
+	on_use = function(_, user, pointed_thing)
 		local paintable = get_entity(user, pointed_thing)
 		if not paintable then
 			return
@@ -219,7 +223,7 @@ minetest.register_tool("epidermis:eraser", {
 })
 
 local function undo_redo_use_func(logname)
-	return function(_itemstack, user, pointed_thing)
+	return function(_, user, pointed_thing)
 		local paintable = get_entity(user, pointed_thing)
 		if not paintable then
 			return
@@ -244,9 +248,9 @@ register_color_tool("epidermis:filling_bucket", {
 	inventory_image = "epidermis_filling_paint.png",
 	inventory_overlay = "epidermis_filling_bucket.png",
 }, function(entity, pixelcoord, color)
-	local index = entity:_get_pixel_index(unpack(pixelcoord))
-	local replace_color = entity:_get_color(index)
-	local to_fill = {[index] = replace_color}
+	local start_index = entity:_get_pixel_index(unpack(pixelcoord))
+	local replace_color = entity:_get_color(start_index)
+	local to_fill = {[start_index] = replace_color}
 	local additions
 	local width, height = entity._.width, entity._.height
 	local function fill(index)
@@ -310,9 +314,14 @@ minetest.register_globalstep(function()
 			local def = wielded_item:get_definition()
 			local range = def.range or 4
 			local eye_pos = moblib.get_eye_pos(player)
-			local raycast = minetest.raycast(eye_pos, vector.add(eye_pos, vector.multiply(player:get_look_dir(), range)), true, def.liquids_pointable)
+			local raycast = minetest.raycast(eye_pos,
+				vector.add(eye_pos, vector.multiply(player:get_look_dir(), range)),
+				true, def.liquids_pointable)
 			local pointed_thing = raycast()
-			if pointed_thing.type == "object" and pointed_thing.ref:is_player() and pointed_thing.ref:get_player_name() == name then
+			if pointed_thing.type == "object"
+				and pointed_thing.ref:is_player()
+				and pointed_thing.ref:get_player_name() == name
+			then
 				-- Skip player
 				pointed_thing = raycast(pointed_thing)
 			end
@@ -364,7 +373,8 @@ register_color_tool("epidermis:rectangle", {
 			local max = modlib.vector.combine(pixelcoord_start, pixelcoord_end, math.max)
 			local dim = max - min
 			local preview = "^[combine:" .. entity._.width .. "x" .. entity._.height
-				.. ":" .. min[1] .."," .. min[2] .. "=epxw.png\\^[multiply\\:" .. color:to_string() .. "\\^[resize\\:" .. (dim[1] + 1) .. "x" .. (dim[2] + 1)
+				.. ":" .. min[1] .."," .. min[2] .. "=epxw.png\\^[multiply\\:" .. color:to_string()
+				.. "\\^[resize\\:" .. (dim[1] + 1) .. "x" .. (dim[2] + 1)
 			entity:_update_texture(preview)
 		end,
 		pixels = function(pixelcoord_end)
@@ -392,22 +402,23 @@ register_color_tool("epidermis:line", {
 		entity = entity,
 		-- A pixel preview is sufficient here as the line may at most have max(width, height) pixels
 		pixels = function(pixelcoord_end)
-			local pixelcoord_start = pixelcoord_start
+			-- This might be copied & swapped. We don't want this to affect the upvalue, so we localize it.
+			local pixelcoord_start_copy = pixelcoord_start
 			-- Uses Bresenham's line algorithm
-			local diff = modlib.vector.subtract(pixelcoord_end, pixelcoord_start)
+			local diff = modlib.vector.subtract(pixelcoord_end, pixelcoord_start_copy)
 			if diff:norm() == 0 then
 				-- Early return: We would divide by zero when obtaining the slope otherwise
-				local idx = entity:_get_pixel_index(unpack(pixelcoord_start))
+				local idx = entity:_get_pixel_index(unpack(pixelcoord_start_copy))
 				return {[idx] = entity:_get_color(idx)}, color_argb
 			end
 			local swapped
 			if math.abs(diff[2]) > math.abs(diff[1]) then
 				swapped = true
-				pixelcoord_start = {pixelcoord_start[2], pixelcoord_start[1]}
+				pixelcoord_start_copy = {pixelcoord_start_copy[2], pixelcoord_start_copy[1]}
 				pixelcoord_end = {pixelcoord_end[2], pixelcoord_end[1]}
 			end
 			local actions = {}
-			local min = pixelcoord_start
+			local min = pixelcoord_start_copy
 			local max = pixelcoord_end
 			if min[1] > max[1] then
 				min, max = max, min