Read/write GUIDs from/to buffers in Luau. Will throw errors for invalid GUIDs if you use the 'strict' version. Depending on the specifics of your use case, if you really love hyper-optimisation you could probably remove the support for allowing/allowing no braces. It does encode the UUID compliance characters (the `4` and the `[89ab]`), but that…

guid-buffer.luau

local GUID_FORMAT = "%08x-%04x-%04x-%04x-%04x%08x"
local GUID_BRACES_FORMAT = "{" .. GUID_FORMAT .. "}"

local GUID_PATTERN = "^{?(%x%x%x%x%x%x%x%x)-(%x%x%x%x)-(4%x%x%x)-([89AaBb]%x%x%x)-(%x%x%x%x)(%x%x%x%x%x%x%x%x)}?$"

local function writeGUID(buff: buffer, offset: number, guid: string)
	if guid:sub(1, 1) == "{" then
		buffer.writeu32(buff, offset, tonumber(guid:sub(2, 9), 16))
		buffer.writeu32(buff, offset + 4, tonumber(guid:sub(11, 14), 16) * 2 ^ 16 + tonumber(guid:sub(16, 19), 16))
		buffer.writeu32(buff, offset + 8, tonumber(guid:sub(21, 24), 16) * 2 ^ 16 + tonumber(guid:sub(26, 29), 16))
		buffer.writeu32(buff, offset + 12, tonumber(guid:sub(30, 37), 16))
	else
		buffer.writeu32(buff, offset, tonumber(guid:sub(1, 8), 16))
		buffer.writeu32(buff, offset + 4, tonumber(guid:sub(10, 13), 16) * 2 ^ 16 + tonumber(guid:sub(15, 18), 16))
		buffer.writeu32(buff, offset + 8, tonumber(guid:sub(20, 23), 16) * 2 ^ 16 + tonumber(guid:sub(25, 28), 16))
		buffer.writeu32(buff, offset + 12, tonumber(guid:sub(29, 36), 16))
	end
end

local function readGUID(buff: buffer, offset: number, braces: boolean?): string
	local a = buffer.readu32(buff, offset)
	local b = buffer.readu32(buff, offset + 4)
	local c = buffer.readu32(buff, offset + 8)
	local d = buffer.readu32(buff, offset + 12)

	local format = if braces then GUID_BRACES_FORMAT else GUID_FORMAT
	local guid = string.format(format, a, b // 2 ^ 16, b % 2 ^ 16, c // 2 ^ 16, c % 2 ^ 16, d)

	return guid
end

strict-guid-buffer.luau

local GUID_FORMAT = "%08x-%04x-%04x-%04x-%04x%08x"
local GUID_BRACES_FORMAT = "{" .. GUID_FORMAT .. "}"

local GUID_PATTERN = "^{?(%x%x%x%x%x%x%x%x)-(%x%x%x%x)-(4%x%x%x)-([89AaBb]%x%x%x)-(%x%x%x%x)(%x%x%x%x%x%x%x%x)}?$"

local INVALID_GUID_ERROR = "Invalid GUID"

local function writeGUID(buff: buffer, offset: number, guid: string)
	local a, b, c, d, e, f = guid:match(GUID_PATTERN)
	assert(a and b and c and d and e, INVALID_GUID_ERROR)

	local firstBlock = assert(tonumber(a, 16), INVALID_GUID_ERROR)

	local secondBlockA = assert(tonumber(b, 16), INVALID_GUID_ERROR)
	local secondBlockB = assert(tonumber(c, 16), INVALID_GUID_ERROR)

	local thirdBlockA = assert(tonumber(d, 16), INVALID_GUID_ERROR)
	local thirdBlockB = assert(tonumber(e, 16), INVALID_GUID_ERROR)

	local fourthBlock = assert(tonumber(f, 16), INVALID_GUID_ERROR)

	buffer.writeu32(buff, offset, firstBlock)
	buffer.writeu32(buff, offset + 4, secondBlockA * 2 ^ 16 + secondBlockB)
	buffer.writeu32(buff, offset + 8, thirdBlockA * 2 ^ 16 + thirdBlockB)
	buffer.writeu32(buff, offset + 12, fourthBlock)
end

local function readGUID(buff: buffer, offset: number, braces: boolean?): string
	local a = buffer.readu32(buff, offset)
	local b = buffer.readu32(buff, offset + 4)
	local c = buffer.readu32(buff, offset + 8)
	local d = buffer.readu32(buff, offset + 12)

	local firstValidator = bit32.extract(b, 12, 4)
	local secondValidator = bit32.extract(c, 28, 4)

	assert(firstValidator == 4, INVALID_GUID_ERROR)
	assert(secondValidator >= 8 and secondValidator <= 11, INVALID_GUID_ERROR)

	local format = if braces then GUID_BRACES_FORMAT else GUID_FORMAT
	local guid = string.format(format, a, b // 2 ^ 16, b % 2 ^ 16, c // 2 ^ 16, c % 2 ^ 16, d)

	return guid
end

what exactly is the use of this

Writing GUIDs to buffers (either for networking or data storage, as GUIDs are common in both areas), encoding them as binary rather than as strings.