CurseForge · Minecraft mod
Offline authenticator
Fixes issues for offline servers.
Quick answer
Which Offline authenticator release should I use?
Offline authenticator offline_authenticator-1.0.0.jar targets 1.20.1 with Forge. The project page does not say whether this file belongs on the client, dedicated server, or both. No extra mods listed for this file.
Where it goes
Is Offline authenticator required on the client, server, or both?
The project page does not say whether this file belongs on the client, dedicated server, or both.
The source does not explicitly classify this release as client-only or server-only.
What else does Offline authenticator offline_authenticator-1.0.0.jar need?
offline_authenticator-1.0.0.jar. Change the file and its required mods may change too.
This file does not list any required mods. Do not add a library just because a different file uses it.
This file does not list any required or optional mods.
Before you install it
Add Offline authenticator without breaking your instance.
Built for Offline authenticator offline_authenticator-1.0.0.jar. Pick another file and the loader, install side or required mods may change.
- 01
Stick to this file
Use offline_authenticator-1.0.0.jar. It targets 1.20.1 with Forge; another release may have different loader, side or dependency requirements.
- 02
Bring the mods it needs
This file does not list any required mods. Do not add a library just because a different file uses it.
- 03
Put it on the correct side
The project page does not say whether this file belongs on the client, dedicated server, or both.
- 04
Pick the file you checked
Use the “Get this file” button beside offline_authenticator-1.0.0.jar. It opens that exact file at the source.
About this project
What does Offline authenticator add?
OFFLINE authenticator
Offline authenticator reimplements whitelist for offline users aswell as making it impossible to spoof other users by changing your username. This gives offline servers a better sense of security and no one can hijack your server by spoofing usernames.
It works like this. Your client sends the server a key (It generates a random key if a key doesnt already exist for that server) and then that key if the user isnt already taken is SAVED under that users name in the server config. But if it IS taken and they send a wrong key for the wrong username they ARENT let into the server and with this i could reimplement whitelist for offline mode.
You dont need to know of the specifications because it is all seamless! If you join a server in offline mode (If ur not spoofing another user) you will join without issue.
BOTH THE CLIENT AND SERVER NEED THIS MOD. Its not like those /register and /login commands but it works similarly it just does all of that stuff automatically BUT if you want to create another instance or keep joining that offline server on another computer you WILL need to copy your offlinepass_client.json file inside of the config.
Project description from CurseForge.
Pick your setup
Offline authenticator by Minecraft version and loader
Choose the version and loader you play, then open the matching release.
Check the dependencies, then try the file in a copied instance before changing a world you care about.
Recent files
Offline authenticator versions and loaders
offline_authenticator-1.0.0.jar
27 Feb 2026
offline_client-1.0.0.jar
offline_authenticator-1.0.0.jar
18 Feb 2026
Looking for an older file? The official CurseForge project page is in Resources.