CustomLag

CustomLag

Fabric mod to simulate lag for servers and single player worlds by delaying packets from sending and receiving

by
1.3K Downloads
fabricgame-mechanicsmanagementutility
Rent Server with this Mod

Screenshots

latency showcase example

About this Mod

About the Mod

This Mod simulates lag by delaying the processes of receiving and sending packets. This is done by injecting a ContextHandler inside the ChannelPipeline of a minecraft connection. This mod works only for servers and single player worlds.

Usage

To set or change the latency/ping for a player, just use the lag command:

/lag set <playername> <latency>

Setting lag will be saved to a toml file, so even after restart, the settings
will remain. You can also set the lag of offline players (who have not currently
joined yet.)

In order to remove the lag of a player, you can use:

/lag remove <playername>

(this removes the ContextHandler that delays packets from sending)

Some additional commands are:

There are also some addional quality of live -ish commands, like increase the
keep alive / ping packets interval, to find more, just enter

/customlag

Available Versions

CustomLag 1.1.1+1.21.6-1.21.8release
MC 1.21.6, 1.21.7, 1.21.8fabric
December 29, 2025
CustomLag 1.1.1 for version 1.21.5release
MC 1.21.5fabric
December 29, 2025
CustomLag 1.1.0 for version 1.21.11release
MC 1.21.11fabric
December 29, 2025
CustomLag 1.1.0 for version 1.21.9 til 1.21.10release
MC 1.21.9, 1.21.10fabric
December 29, 2025
CustomLag 1.1.0 for version 1.21.5 til 1.21.8release
MC 1.21.5, 1.21.6, 1.21.7, 1.21.8fabric
December 29, 2025

How to Install CustomLag on Your Server

1

Order Server

Order a Minecraft Java server with at least 3 GB RAM (4 GB recommended).

2

Set fabric Loader

In the panel under "Egg", select the fabric loader and matching Minecraft version (1.21.11).

3

Install Mod

Open the mod browser in the dashboard and search for "CustomLag". Click "Install" – done! Alternatively, upload the .jar via SFTP to the /mods folder.

Compatibility

Mod Loaders

fabric

Minecraft Versions

1.21.11, 1.21.10, 1.21.9 (+9 more)

Server-side

Required

Recommended RAM

4 GB(min. 3 GB)

Frequently Asked Questions

CustomLag server crashes on startup – what to do?

Most common cause: wrong fabric version or insufficient RAM. Check the server log (latest.log) for "OutOfMemoryError" or "Mixin" errors. With Mado Hosting: ensure at least 3 GB RAM is allocated and the loader matches the mod version (1.21.11). You can switch loaders with one click in the panel.

Is CustomLag compatible with fabric?

CustomLag officially supports fabric for Minecraft 1.21.11, 1.21.10, 1.21.9. The Mado dashboard automatically detects incompatible loader combinations.

Server lagging with CustomLag – how to optimize performance?

Recommended RAM: 4 GB (per 8 players). Use /spark profiler to check if CustomLag consumes the most tick time. Common fixes: reduce server view-distance to 8-10, install "performant" or "starlight" as supplementary mods on Forge. With Mado Hosting, your server runs on NVMe SSDs with dedicated CPU cores for minimal latency.

Rent Modded Server

Install CustomLag with just one click on your server.

Recommended RAM
4 GBab €8/mo
Min. 3 GB | +1 GB pro 8 Spieler
Create Server Now
1-Click Mod Install
NVMe SSD Storage
DDoS Protection included

Details

License
MIT License
Server-side
Required

Supported Versions

1.21.111.21.101.21.91.21.81.21.71.21.61.21.51.21.41.21.31.21.2+2 more