Compared with hand-written buffers

Writing to a buffer by hand is not hard, and code you write yourself for one event can be as fast as anything BlinkBlox generates for it. Speed is not the reason to use a compiler.

The reason is the receiving side. A writer has one input, yours. A reader on the server has whatever a client chose to send.

Where writing it by hand is fine

• The sender is the server. A client reading the server’s packets has nothing to defend against.
• You have one or two remotes and no wish to add a build step for them.
• The payload is one fixed shape, a few numbers at known offsets, with nothing variable in it.

In those cases a compiler saves you little. Use what you have.

What a reader has to get right

Take one event: a client reports a hit with a target, an amount from 1 to 100 and a short note.

event Damage {
  From: Client,
  Type: Reliable,
  Call: SingleSync,
  Rate: 10,
  Data: struct { Target: Instance(Humanoid), Amount: u8(1..100), Note: string(0..32) }
}

The reader most people write first:

Remote.OnServerEvent:Connect(function(Player, Packet: buffer, Target: Humanoid)
  local Amount = buffer.readu8(Packet, 0)
  local Length = buffer.readu8(Packet, 1)
  local Note = buffer.readstring(Packet, 2, Length)

  Combat.Apply(Player, Target, Amount, Note)
end)

It works for every packet your own client sends. An exploiter does not run your client:

What arrives	What this reader does
Amount of 0 or 255	Passes it on. Nothing compares it with 1 and 100.
A Part, a string or nothing where Target should be	Passes it on. A type annotation is not checked when the code runs.
The same call 500 times a second	Runs Combat.Apply 500 times a second.
A string, or a buffer one byte long, as Packet	Throws, and prints an error with a stack trace each time it is sent.

Each of those is a few lines to fix. The ones below are easier to miss, and none of them shows up until the payload grows past this example:

• A count read before the allocation it sizes. table.create(buffer.readu16(Packet, 0)) gives a client 65535 slots for two bytes. The count has to be compared with its bound, and with the bytes left in the packet, before anything is allocated.
• A float’s range. if X < -1 or X > 1 then return end lets NaN through, because NaN compares false both ways. The check has to be written not (X >= -1).
• Several events in one buffer. A remote call costs about 11 bytes beside its payload, so packing a frame’s events into one buffer is most of what buffer networking saves. Once you do, a throw halfway through the buffer loses every event after it, and those may belong to an honest player’s inputs. The loop needs a pcall and a decision about what was already delivered.
• Telling the game. Refusing a packet silently means nobody learns who is sending them. Reporting every one means a client can call your handler, or fill your output, hundreds of times a second.
• Two copies of every offset. The writer on the client and the reader on the server each spell out the layout. Change one field and forget the other side, and the server decodes one value as another without an error.

None of this is beyond anyone who can write the first reader. It is the same dozen lines again in every remote, and one forgotten check is enough.

What the compiler writes instead

This is the reader BlinkBlox generates for Damage, copied from its output. The two fixed-size fields share a block that is read once, as BLOCK_START:

do
  -- Value.Amount: Amount
  local Checked = buffer.readu8(RecieveBuffer, BLOCK_START + 0)
  if not (Checked >= 1) then error(`Expected "Value.Amount" to be larger than or equal to 1, got {Checked} instead.`) end
  if not (Checked <= 100) then error(`Expected "Value.Amount" to be smaller than or equal to 100, got {Checked} instead.`) end
  Value.Amount = Checked
end
do
  -- Value.Note: Note
  local Length = buffer.readu8(RecieveBuffer, BLOCK_START + 1)
  if Length > 32 then error(`Expected length of "Value.Note" to be smaller than or equal to 32, got {Length} instead.`) end
  if Length > buffer.len(RecieveBuffer) - RecieveCursor then error(`Expected "Value.Note" to fit in the {buffer.len(RecieveBuffer) - RecieveCursor} bytes left in the packet, got a length of {Length} instead.`) end
  Value.Note = buffer.readstring(RecieveBuffer, Read(Length), Length)
end

The target is checked for being an Instance and for its class:

elseif not (Value.Target :: Instance):IsA("Humanoid") then
  error(`Expected an Instance of type "Humanoid", got "{Value.Target.ClassName}" instead.`)
end

And the listener is reached only past the event’s rate limit:

local Value: { Target: Humanoid, Amount: number, Note: string } = SerdesFunctions.ReadEVENT_Damage()
if RateAccept(Player, 1, 10, 10, "Damage") == true then

That is all there is to it: locals, functions and buffer calls, the code you would write by hand with the checks already in it. A generated module has no classes and no metatables, and needs no runtime library beside it. Its API is tables of functions, called with a dot – Net.Damage.Fire(...), never Net.Damage:Fire(...).

The error calls above never leave the module. The whole packet is decoded inside one pcall, an event at a time: the events before the bad one are delivered, the rest of the packet is dropped, and your handler is told which player sent it, at most once a second. The full order of checks is in Securing the server.

What stays yours

BlinkBlox makes sure a value is well-formed. Whether it is legitimate is still the game’s to decide: an Amount of 100 is in range whether or not the player’s weapon can deal it, and Target is a Humanoid whether or not it is in reach. See What BlinkBlox does not protect you from.