Error Codes › Outdated server! / Outdated client!

Outdated server! / Outdated client!

JOIN-005 · Outdated server / client

'Outdated server! I'm still on...' or 'Outdated client! Please use...' means the player and the server run different Minecraft versions. How to match them, and when ViaVersion helps.

What it looks like in the log

Outdated server! I'm still on 1.21.4
Outdated client! Please use 1.21.4
Incompatible client! Please use 1.21.4

What it means

Minecraft only lets a game join a server of the same version. The message names the version the server is on: "Outdated client" means the player is behind it, "Outdated server" means the server is behind the player. The network is fine; the two just don't speak the same protocol.

How to fix it

Switch the player's version. In the launcher, make a profile for the exact version the message names. That is the quickest fix for one player.
Or move the server. Upgrade it to the newer version, or create a new server on the version your players have. Take a backup before upgrading, since worlds can't be taken back to an older version.
Modded servers are stricter. Everyone needs the same Minecraft version, the same loader (Fabric, Forge, NeoForge) and the mods the server requires. See modded server setup.
Let several versions in. On a Paper or Spigot-family server, the ViaVersion plugin lets newer clients join an older server, and ViaBackwards lets older ones join a newer server. It isn't perfect, and it doesn't apply to vanilla or modded servers.
Bedrock says the same thing when a phone, console or PC is on a different release than the dedicated server. Update the server, or the game, until they match. For Java players joining a Bedrock-side world, see the crossplay guide.

More help

Coalstack's Auto Debugger scans a Java server's log for known errors like this one and links straight to the fix. Download Coalstack to try it.