Run the test above for at least 60 seconds. Here is what each
number means for this game specifically.
Packet loss (the desync risk)
In a lockstep model, every input has to reach every machine, in order. Loss forces retransmission and stalls the shared clock, and in the worst case leaves a client computing from an incomplete picture. That is the road to a desync, and a desync is not a hitch - it is a forced re-download of the map.
Ping (what latency hiding does and does not cover)
Factorio deliberately shows your own actions immediately rather than waiting for confirmation, so building and walking feel responsive at latencies that would be intolerable otherwise. What it cannot hide is anything that depends on the shared simulation agreeing - which is why some actions feel instant and others do not.
Jitter (a clock everyone shares)
Because all machines must advance in step, the group runs at the speed of its slowest link. Uneven delivery from any one player produces stutter for everyone, and the game will tell you when it is waiting. That makes a single unstable connection a shared problem in a way most games avoid.
What you see in game, and which number on this page explains it.
Nearly every game in this catalogue works the same way at heart. A server holds the authoritative state, clients receive updates about the parts of it they can see, and the amount of data grows with how much is happening. Factorio would be a catastrophe under that model - a large factory has tens of thousands of belts, inserters and machines all changing state constantly, and streaming that to every player is not feasible.
So it does the opposite. Every machine runs the identical simulation from the identical starting point, and the only thing sent over the network is what the players did. Because the simulation is deterministic - the same inputs always produce the same outputs, on every machine, in the same order - everyone arrives at the same factory without ever being told what it looks like. The bandwidth cost of an enormous base is essentially the same as an empty map.
The price is that determinism is all-or-nothing. There is no such thing as being slightly out of sync: either your simulation matches or it does not, and once it does not, every subsequent tick diverges further. The game therefore checks continuously, and when it finds a mismatch it stops you, writes a report, and gives you the whole map again from the authoritative machine. That is what a desync is, and why it is so much more disruptive than the equivalent event elsewhere.
For diagnosis this has one useful consequence and one counter-intuitive one. The useful one: your own actions are shown immediately through latency hiding, so raw ping matters far less than you would expect for a game this precise. The counter-intuitive one: bandwidth is irrelevant and speed tests are actively misleading. What decides whether Factorio multiplayer works is whether small packets arrive, in order, reliably - which is exactly the three numbers on this page.
If the chart above shows packet loss or high jitter, work through
these in order.
What causes a desync in Factorio?
A desync means your machine's simulation stopped producing identical results to everyone else's. Mismatched mods are the most common cause, and connection problems that leave a client working from incomplete input data are the other. The game writes a report when it happens.
Why does Factorio multiplayer use so little bandwidth?
Because it does not send you the state of the world. Every machine runs the same deterministic simulation and only player inputs are exchanged, so a factory with tens of thousands of moving parts costs no more to transmit than an empty map.
Why do my own actions feel instant but others do not?
The game deliberately shows your own inputs before they have been confirmed by the shared simulation, a technique usually called latency hiding. Anything that depends on agreement between machines cannot be treated that way, which is the difference you are feeling.
Does one player's bad connection affect everyone?
Yes, more directly than in most games. All machines must advance in step, so the session runs at the pace of its slowest participant and the game will show that it is waiting for someone.