The Zombies group sets what the dead are like: how fast they move, how hard they hit, what they can see and hear, how the infection works and what they can break. How many zombies there are is Zombie Population under Game Settings, not here: How to change zombie population, respawn and loot respawn on your Project Zomboid server.

Open the editor

Open your server in the panel and click the Settings tab.
In the list on the left, under Config files, click Sandbox Settings. The file name is shown at the top.
If the list says No config files yet, start the server once. The game writes its sandbox file the first time it runs.

The Config files list on the Project Zomboid Settings page with Server Settings and Sandbox Settings

The editor only saves while the server is stopped. Stop the server, change the settings below, then click Save only or Save & start. The full steps are in How to change Project Zomboid sandbox settings in the panel. Headings such as Zombies appear in capitals in the editor. The editor shows Build 42 files only: on a Build 41 server it opens with a message that the file is from a different build, see Project Zomboid Sandbox Settings says the file is from a different build.

Every setting in Zombies

Setting	What it does	Values	A new server starts with
Speed	How fast zombies move.	Sprinters, Fast Shamblers, Shamblers, Random	Random
Sprinters with random speed (%)	With Speed set to Random, the percentage of zombies that are sprinters.	A whole number from 0 to 100	0
Strength	The damage zombies inflict per attack.	Superhuman, Normal, Weak, Random	Normal
Toughness	The difficulty of killing a zombie.	Tough, Normal, Fragile, Random	Random
How the infection spreads	How the Knox Virus spreads.	Blood and Saliva, Saliva Only, Everyone's Infected, None	Blood and Saliva
Time from infection to death	How quickly the infection takes effect.	Instant, 0-30 Seconds, 0-1 Minutes, 0-12 Hours, 2-3 Days, 1-2 Weeks, Never	2-3 Days
Time from death to rising	How quickly infected corpses rise as zombies.	Instant, 0-30 Seconds, 0-1 Minutes, 0-12 Hours, 2-3 Days, 1-2 Weeks	0-1 Minutes
Intelligence	Zombie intelligence.	Navigate and Use Doors, Navigate, Basic Navigation, Random	Basic Navigation
Memory	How long zombies remember a player after seeing or hearing them.	Long, Normal, Short, None, Random, Random between Normal and None	Normal
Sight	Zombie vision radius.	Eagle, Normal, Poor, Random, Random between Normal and Poor	Random between Normal and Poor
Hearing	Zombie hearing radius.	Pinpoint, Normal, Poor, Random, Random between Normal and Poor	Random between Normal and Poor
Active during	Whether zombies are more "active" during the day or night. "Active" zombies will use the speed set in the "Speed" setting. "Inactive" zombies will be slower, and tend not to give chase.	Both, Night, Day	Both
Crawl under cars	How often zombies can crawl under parked vehicles.	Crawlers Only, Extremely Rare, Rare, Sometimes, Often, Very Often, Always	Often
Break player buildings	If zombies can destroy player constructions and defenses.	On or off	On
Set off house alarms	If zombies trigger house alarms when breaking through windows or doors.	On or off	On
Drag players down	If multiple attacking zombies can drag you down and kill you. Dependent on zombie strength.	On or off	On
Fake dead zombies	Whether some dead-looking zombies will reanimate and attack the player.	World Zombies, World and Combat Zombies, Never	World Zombies
Distribution	How zombies are distributed across the map.	Urban Focused, Uniform	Urban Focused
Migrate to empty areas	Zombies can wander into parts of the map that have been cleared.	On or off	On

The settings that change difficulty most

Speed (Sprinters, Fast Shamblers, Shamblers or Random), Strength and Toughness.
Sight, Hearing and Memory decide how easily zombies find and follow a player.
How the infection spreads, Time from infection to death and Time from death to rising decide how dangerous a bite is.

For a quick change to the whole difficulty, apply a preset first: How to choose a sandbox preset for your Project Zomboid server.

Good to know

Most sandbox rules apply from the next start. A few, such as the start date and the months since the outbreak, only matter when a new world is created.
Four sandbox values are not in this editor, because the panel writes them at every start: Zombie Population, Zombie Respawn, Loot Respawn (hours) and Banned Item IDs. They are under Settings, then Game Settings: How to change zombie population, respawn and loot respawn on your Project Zomboid server.
The column "A new server starts with" shows the value a new server has before you change anything (the game's Apocalypse rules). If you applied a preset, your values differ: How to choose a sandbox preset for your Project Zomboid server.
Back up first if the world has progress in it: How to back up and restore your Project Zomboid world.

How to change the zombie settings of your Project Zomboid server

Open the editor

Every setting in Zombies

The settings that change difficulty most

Good to know

CREATE YOUR GAME SERVER
READY TO GET STARTED?

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Open the editor

Every setting in Zombies

The settings that change difficulty most

Good to know

CREATE YOUR GAME SERVERREADY TO GET STARTED?

OUR LATEST BLOGS

Best Factorio Mods for Multiplayer Servers in 2026

Terraria Optimization & Hosting Guide 2026: Best Settings, Specs, and Server Tips

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CREATE YOUR GAME SERVER
READY TO GET STARTED?