🎮 Game Error Codes What it means & how to fix it

Terraria Multiplayer Won't Connect? Here's the Fix

Nine out of ten Terraria "can't join" problems come from one of three things: the two players are on different game versions (or one is on tModLoader), the host's port 7777 is blocked, or you're trying to connect by IP when Steam invites would just work. The fastest fix: make sure both players are on the exact same version, then have the host use Steam > Multiplayer > Host & Play and send a Steam invite instead of typing an IP. If you must use a dedicated server, forward TCP port 7777. Steps below, in order.

Terraria multiplayer — exact port & world path

Port to forward (TCP)
7777
Protocol
TCP (Terraria host uses a single TCP port)
World files path (Windows)
%USERPROFILE%\Documents\My Games\Terraria\Worlds
Steam vs dedicated
Steam 'Host & Play' uses Steam relay (no port needed); the tModLoader/dedicated server needs 7777 open
Common cause
Host on Steam relay but friend joins by IP — use the same join method as the host chose

Last verified: September 2026

Error codes

Lost connection / connection timed out The client reached the host but the session dropped before the world loaded

Cause: Almost always a version mismatch (one player updated, the other didn't, or one is on tModLoader) or a firewall blocking port 7777 on the host.

Fix:
  1. Check both players' versions: main menu shows the version bottom-left. They must match exactly.
  2. If one player uses tModLoader, BOTH must launch tModLoader (it is a separate app from vanilla Terraria).
  3. Host: allow Terraria through Windows Defender Firewall (Settings > Privacy & security > Windows Security > Firewall > Allow an app).
  4. Prefer Steam hosting (Host & Play) so Steam tunnels the connection and no port forwarding is needed.
You cannot connect because the world is being used The world file is locked by another running instance

Cause: A dedicated server or a second Terraria instance still has the world open.

Fix:
  1. Close every Terraria and TerrariaServer.exe process (Task Manager > End task), then restart only the host.
  2. If you run a dedicated server, do not also open the same world in the client at the same time.

Fixes that work for most Terraria errors

  1. Match versions: both players on identical Terraria (or both on tModLoader). A mismatch silently blocks the join.
  2. Host over Steam: Multiplayer > Host & Play, then invite the friend from the Steam overlay — this avoids all port/IP issues.
  3. If joining by IP: the host runs a dedicated/Host & Play server and forwards TCP port 7777 on their router to the host PC's local IP.
  4. Allow Terraria (and TerrariaServer.exe) through the host's firewall and any antivirus.
  5. Both players verify game files: Steam > right-click Terraria > Properties > Installed Files > Verify integrity.
  6. Use the host's public IP (whatismyip) for internet play, or the 192.168.x.x local IP only for same-network LAN.
  7. If it broke after an update, wait until both players' Steam has finished updating to the same build before retrying.

FAQ

Why can't I join my friend's Terraria world?

Most often you're on different game versions or one of you is running tModLoader while the other runs vanilla. Confirm both show the same version on the main menu, and if mods are involved both must launch tModLoader.

Do I need to port forward for Terraria multiplayer?

Not if the host uses Steam's Host & Play and sends a Steam invite — Steam tunnels the connection. Port forwarding (TCP 7777) is only needed for a dedicated server that players join by IP.

What port does Terraria use?

TCP port 7777 by default. If you host a dedicated server for internet play, forward 7777 on your router to the host PC and allow it through the firewall.

Terraria says the world is being used — what do I do?

Close all Terraria and TerrariaServer.exe processes in Task Manager, then start only the host. The world file can only be open in one instance at a time.

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