How many zombies there are, how fast they are, how much loot is lying around and whether zombies come back – all of this is in the sandbox settings of your Project Zomboid server. There's no single difficulty slider: the difficulty results from these values.

Opening the file

Stop the server.
Files tab → folder .cache/Server/ → file <servername>_SandboxVars.lua → Edit. The server name is the value of the startup variable Internal server name (SERVER_NAME) – you'll find it in the Startup variables tab.
Only change the value after the = and leave commas and curly braces in place.
Save and start the server.

If the file is missing, start the server once and stop it again – then it's created.

Tip: Most entries have a comment above them (lines starting with --) explaining the allowed values, e.g. which number means “Normal” or “High”. Stick to these.

Zombies

Entry	Meaning
`Zombies`	Base zombie population (from “none” to “insane”)
`ZombieConfig` → `PopulationMultiplier`	Fine control for the amount, `1.0` = normal
`ZombieConfig` → `PopulationPeakDay`	The day on which the most zombies are around
`ZombieLore` → `Speed`	Speed: sprinters, fast shamblers or shamblers
`ZombieLore` → `Strength`, `Toughness`	How strong and how tough zombies are
`ZombieLore` → `Transmission`	How you get infected (or not at all)

Zombie respawn

Entry	Meaning
`ZombieConfig` → `RespawnHours`	After how many in-game hours zombies return to cleared areas. `0` = never
`ZombieConfig` → `RespawnUnseenHours`	How long an area must be unobserved before new zombies appear there
`ZombieConfig` → `RespawnMultiplier`	Which share of the zombies comes back each time

Loot

Entries with Loot in their name control how much food, weapons and other items are found in containers.
LootRespawn sets whether and how often looted containers are refilled.

The exact names and allowed values are in the comments of your file – they depend on the game version.

More popular values

Entry	Meaning
`DayLength`	How long an in-game day lasts in real time
`WaterShutModifier` / `ElecShutModifier`	After how many days water and power go out
`StartMonth`	The month the game starts in

Easier: set it up in the game and upload

Prefer clicking? Set the sandbox options on your PC in the game under Host and save them. The game stores the file in your user folder under Zomboid/Server/. Then upload it in the Files tab to .cache/Server/ and rename it so that it's named exactly like your previous <servername>_SandboxVars.lua (download or replace the old one first).

Good to know

Back up first: Create a backup before making changes.
Existing world: Loot that has already been generated in visited areas stays as it is – you'll mainly notice more or less loot in areas nobody has entered yet. For a complete fresh start with new rules, change the Internal server name (letters and digits only, no spaces) – the server then creates a new world with new, empty settings.
Server name, admin account and updates: Project Zomboid: connect to and set up your server. Mods: Installing mods from the Workshop.
If the server no longer starts after a change, the error is usually shown in the Console – often it's a missing comma.

No server yet? You can test the Project Zomboid server free for 24 hours – how it works. To order: Rent a Project Zomboid server.

Project Zomboid: Sandbox settings – zombies, loot, respawn and difficulty