Eye Spy
This mod adds useful functionality for the spyglass that works exclusively on the server side. It is compatible with Fabric and Quilt, making it a versatile solution for many game servers.
Main Features
All features work without the need to install the mod on the client. Settings can be changed directly in the game using the /eyespy config command (available to operators) or by editing the configuration file config/eyespy.json5.
Ping System


Players can now mark blocks and entities through the spyglass using the reassigned "Swap Item with Offhand" key. This displays a glowing outline visible to the player themselves and others, showing the distance to the target and, optionally, its description. Double-tapping the key creates a flashing red hazard ping.
If a player installs Eye Spy on their client, they will get a separate key for pings instead of using the "Swap Item with Offhand" functionality. This is completely optional and does not affect other players.
Rangefinder

When using the spyglass, players now see the distance to the targeted block or entity, as well as their names if available.
Supported Versions
The mod is designed for versions 1.20.4, 1.20.2, 1.20.1, and 1.19.4. Since it heavily uses Display Entities, porting to earlier versions would most likely require a complete rewrite.
Requirements
Includes several JackFredLib modules and Server Translation API.