Lag Goggles is a great additional mod that we use outside of the FTB pack. It allows us to track down troublesome lag on the server.

How to get:

1) Download

   Go to this link and download the file
   [[https://minecraft.curseforge.com/projects/laggoggles/files/2529035]]
   File name: LagGoggles-FORGE-1.12.2-3.1.jar
   

2) Install

   Drop the file into your minecraft/mods folder. 
   Re-launch minecraft.  You should see the mod LagGoggles listed in your Mods list after Minecraft re-loads.
   

3) Config

   The next time you launch Minecraft, you will need to find the keybinding "Profile GUI" (I use Home key)
   

4) How to use?

   Once you've logged into the server, hit your new keybinding you setup in step 3.
   
   {{:wiki:laggoggles_ui.png?nolink&400|}}
   
   Clicking on the little down-facing arrow will allow you to see the lag overlay.
   

FAQ Q) Why isn't the block s/t updating? A) The server polls all blocks and mods and generates a static profile. You are seeing this profile.

Q) How do I update the Profile? A) Right now only an OP can update, but this may change soon.

Q) What are the big coloured clouds in the sky when I have the overlay active? A) These are generalized chunk indicators. They indicate “laggiest” chunks.

Q) What does the s/t mean?
A) This is the amount of lag being generated by the object. Anything over 20 technically generates lag. But anything under 100 is considered “ok”.

Q) How do I use this info to reduce server wide lag and help the community because I love them and they are the family that loves me back when my own family doesn't call me for months on end while I starve and eat only ramen? A) Anything that does something uses ticks. So make sure that when you are setting up machines, or auto farmers (for example) that you either manually turn them off when not using them, or have them set to automatically turn off when the inventory of whatever it is you are farming reaches your desired threshold.