How to Host a Project Zomboid Game for Friends (and Fix Join Problems)
Host runs a real server on your PC while you play, and your friends join through Steam invites. It's the quickest way to play as a group. The most common questions are how much server memory to set and why a friend can't join; here are both, plus the rest of the usual problems.
How to host a game, step by step
Go to “Host”
In the main menu. At the top you choose your username (the one the others will see) and the server name, which is also the name of the save and of its settings files.
Set up the settings
With “Manage Settings” you create or edit that server's settings: zombies, loot, PvP, Workshop mods and maps. They're saved separately and kept for next time. If you're not sure what to pick, see which settings to start with for friends.
Choose the memory
The server memory setting is the RAM your PC sets aside for the server, separate from the game's. More on that below.
Start
Click start. The first time it takes a while: it generates the world and, if there are mods, downloads them. Then you choose where to spawn and create your character.
Invite
Inside the game, Esc → “Invite Friends” and choose who from your Steam list. Your friend has to be in the game's main menu to accept: with a game already open, the invite doesn't come through.
Rather not set it up yourself? Project Zomboid servers from €12 a month, no contract and a full refund within 72 hours. Or create a free Project Zomboid server, no card needed.
How much server memory to set
The server memory setting is the same as the -Xmx of a dedicated server: the maximum Java can use for the world, the zombies, the mods and everything you do. Too little and everyone gets stutters that get worse over the hours; too much and you take RAM away from the game and from Windows, and you're the one who stutters.
With Build 42, the server on its own already asks for a lot: we measured it on 4 GB with barely half a gig to spare, which is why we don't give any Zomboid server less than 6 GB. As a rough guide, on a PC with 16 GB, give the server 6 GB if the game still runs well, or 5 if not, knowing it will have little headroom; with 8 GB of RAM in total, hosting and playing at the same time on Build 42 is very tight.
With lots of mods or extra maps, raise the memory, and if you have nowhere to take it from, that's the sign the server needs to live somewhere else. The Project Zomboid RAM guide explains how to tell if you're short.
My friend can't join my game
Same version and same branch: the version is shown at the bottom of the main menu. If one of you is on a Steam beta (Properties → “Game Versions & Betas”) and the other isn't, you won't see each other. How to get on the same version.
The invite: they have to accept it from the main menu, not with another game open, and you have to send it from “Invite Friends” inside the game. If it doesn't reach them, they can join from their Steam friends list with “Join Game”.
The mods: when they join, the game downloads them. If it hangs while loading or kicks them out, it's usually a mod that won't download or isn't the same version: remove the last ones you added and try again.
The network: with a Steam invite you normally don't need to open ports. If it still won't connect, try Steam Relay in the connection options, and let the game through Windows Firewall when it asks. The other cases are in can't connect to a Project Zomboid server.
Password, whitelist and who gets in
With Host, the server password doesn't count: the game itself says so in that option's help text. People join through Steam invites, so only those you invite get in (or a Steam friend who joins from your profile).
To really lock the server, with a password and a whitelist, you need a dedicated server: private server with a password and whitelist.
Stutters when playing with Host
Your PC runs the game and the server at the same time, so whatever you take from one, the other notices. If everyone feels the stutters and they get worse over the hours, it's the server memory. If only you feel them, lower the game's graphics. If the zombies move in slow motion for everyone, the processor can't keep up: the lag guide says what to turn down.
Where the hosted game is saved
In the Zomboid folder in your user profile: the save in Saves\Multiplayer\<server name> and its settings in Server (the .ini and the SandboxVars). They're the same files a dedicated server uses, so the game can be moved to one without losing the world: how to move your save to a server.
When to stop hosting and get a server
When your friends want to play without you (with Host, if you quit, it's over for everyone), when your PC can't handle the game and the server at once, or when the game is going to last weeks. The options: the free dedicated server on a PC you leave on (how to set it up) or a rented one.
On NapNodes there's a free Project Zomboid server with 6 GB that you start when you want to play, and 6 and 8 GB plans that are always on, with backups. Your hosted save is uploaded from “Files”.
Frequently asked questions
How do I invite friends with Host in Project Zomboid?
Inside the game, Esc → “Invite Friends” and choose who from your Steam list. Your friend has to accept from the game's main menu, not with another game open.
How much server memory should I set in Project Zomboid?
With Build 42, the server runs just under 6 GB. On a 16 GB PC, 6 GB if the game still runs well (5 if not, with little headroom); with lots of mods or maps, more. Stutters for everyone that get worse over the hours are a sign it's short.
Can my friends play when I'm not on?
No: with Host the server lives on your PC and closes when you quit. For them to join without you, you need a dedicated server, on a PC that stays on or rented.
Why can't I set a password with Host?
Because with Host the server password isn't used: people join through Steam invites. The password and the whitelist are for dedicated servers.
Can I move a hosted game to a dedicated server?
Yes: you upload the Saves\Multiplayer\<name> folder and the settings to the server. The guide to moving your save explains it step by step.
Shall we set it up for you?
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Not sure whether your server is online? Check it in a second with the Project Zomboid server status checker: players, version and password, free.