Minecraft anticheat guide
Repeated and Invalid Value Aimbot Checks Explained
How FairPlay's repetition and invalid-value aimbot checks read repeated packets, identical deltas and impossible values, and how staff should review them.
What do repetition and invalid-value checks look at?
These seven checks look for values that repeat too exactly or that a normal client should not send at all. Some read repeated deltas, identical values across consecutive moves, or duplicate movement packets. Others read invalid pitch, non-finite values or precision patterns that a real client does not produce.
The family covers Generic, Identical, Randomization, Aimbot Duplication, Yaw Diff Set, Aimbot Invalid and Precise NaN Window. Several overlap in what they observe, but each one looks at a different kind of repetition or impossibility.
An alert from this family describes the data the server received. Network behavior and client quirks can produce the same data, so the alert is a question about the source.
Which cheat behavior do these checks target?
The family targets output that repeats in a way a human hand does not, or that uses values outside what a client can send. Software that reuses one computed delta, or that sends duplicate movement updates to shape the view, can leave that trace. Identical and Yaw Diff Set look at repeated values across moves. Duplication looks at duplicate movement packets during and around combat.
Invalid-value checks target a different problem. Aimbot Invalid reads pitch values and micro-pitch behavior that a normal client should not send. Precise NaN Window reads windows of samples for values that cannot come from a standard client input path. Both are about impossibility rather than style.
Which legitimate sources can produce repeated or odd values?
Network behavior is the first innocent cause. Packets can arrive duplicated or in bursts, and a player on a poor connection may show repeated movement updates that look like duplication. A proxy or a reconnect can also resend recent state.
Client mods and client builds are the second cause. Some mods change how the client reports rotation, and a few produce values that are unusual but legitimate for that client. A server that acts on these alerts without checking the mod list will punish players who did nothing wrong.
Idle play is the third. A player who stands still or holds a fixed view produces identical deltas for a while. Identical and Generic read repeats over windows, and idle play fills windows with repeats.
How should staff review a repetition alert?
Start with the source. Ask whether the player was on a stable connection, whether the alert coincides with lag, and whether the player uses any client mod. Then check whether the repeats happened during combat or while the player was idle. Repeats that appear only during idle play are weak evidence of anything.
The table below lists the common sources and the first thing to verify for each alert type.
| Alert type | Common legitimate source | First check before acting |
|---|---|---|
| Identical or Yaw Diff Set | A held view or idle play | Whether the repeats fell inside combat or idle time |
| Duplication | Duplicate or bursty packets from a poor connection | Connection record for the same minute and any lag evidence |
| Generic or Randomization | Idle play or a fixed camera on a mount | Activity during the window and the player's position |
| Aimbot Invalid or Precise NaN Window | A client mod or an unusual client build | The player's client and mod list, checked against the server's policy |
What should change only in staging?
Repetition checks depend on window size, on how many repeats count, and on how the family treats idle time. Test those settings with recordings of idle play, lag, combat and mod use. A change that makes the family quieter may also make it miss the pattern you care about, so every change needs the same replay set before and after.
Invalid-value checks should be tested with a clean client and a list of the mods your server allows. Without that list, you cannot tell an odd client from an odd cheat.
What can an invalid-value alert conclude?
An invalid-value alert means the server received data that a standard client path does not produce. It does not say which software produced the data. The honest next step is to find the source, not to assume it. Ask about mods, check the client build and look at the connection record.
Record the source you confirmed, and record the alert as unresolved if you could not confirm it. An unresolved note is more honest than a verdict that the record cannot support.
FAQ
Can a laggy connection trigger the duplication check?
Yes. Bursty or duplicated packets from a poor connection can look like duplicate movement. Check the connection record for the same minute before reading the alert as a pattern.
Why would a legitimate client produce an invalid pitch?
Some client mods and unusual client builds report rotation in ways the standard path does not. The invalid-value checks read the data, not the software, so the client and mod list must be checked.
Do idle players cause identical-delta alerts?
They can. A player holding a fixed view produces identical deltas for a while. Confirm whether the repeats fell during combat before treating them as meaningful.