Debugging & Testing Your Mod

Summary: This tutorial teaches you how to debug and test DayZ mods effectively. You will learn to read script logs, use Print debugging, work with DayZDiag and file patching for rapid iteration, diagnose common error messages, and establish a reliable testing workflow. No IDE debugger exists for retail builds -- your tools are script logs, Print statements, Workbench, DayZDiag, and file patching.

Introduction
The Script Log -- Your Best Friend
Print Debugging (The Reliable Method)
DayZDiag -- The Debug Executable
File Patching -- Edit Without Rebuilding
Workbench -- Script Editor and Debugger
Common Error Patterns and Solutions
Testing Workflow
In-Game Debug Tools
Pre-Release Checklist
Common Mistakes
Next Steps

Introduction

Unlike Unity or Unreal, the retail DayZ executable does not support attaching a debugger to Enforce Script. Instead, you rely on five tools:

Script logs -- Text files capturing every error, warning, and Print output
Print statements -- Trace execution flow and inspect variable values
DayZDiag -- Diagnostic build with enhanced error reporting and debug tools
File patching -- Edit scripts without rebuilding your PBO every time
Workbench -- Official script editor with syntax checking and a script console

Together they form a powerful toolkit. This chapter teaches you how to use each one.

The Script Log -- Your Best Friend

Every time DayZ runs, it writes a script log file. This file captures every script error, warning, and Print() output. When something goes wrong, the script log is the first place to look.

Where to Find Script Logs

Client logs: %LocalAppData%\DayZ\ (press Win+R, paste, Enter)

Server logs: Inside your server's profile folder (set via -profiles=serverprofile)

Files are named script_YYYY-MM-DD_HH-MM-SS.log -- the most recent timestamp is your latest session.

What to Look For

Script logs contain thousands of lines. You need to know what to search for.

Errors are marked with SCRIPT (E):

SCRIPT (E): MyMod/Scripts/4_World/MyManager.c :: OnInit -- Null pointer access

This is a hard error. Your code tried to do something invalid and DayZ stopped executing that code path. These must be fixed.

Warnings are marked with SCRIPT (W):

SCRIPT (W): MyMod/Scripts/4_World/MyManager.c :: Load -- Cannot open file "$profile:MyMod/config.json"

Warnings do not crash your code, but they often indicate a problem that will cause issues later. Do not ignore them.

Print output appears as plain text without any prefix:

[MyMod] Manager initialized with 5 items

This is output from your own Print() calls. It is the primary way you will trace what your code is doing.

How to Search Efficiently

Script logs can be tens of thousands of lines. Never read line by line -- search for your mod prefix or error markers:

powershell

# PowerShell -- find all errors in the latest log
Select-String -Path "$env:LOCALAPPDATA\DayZ\script*.log" -Pattern "SCRIPT \(E\)" | Select-Object -Last 20

# PowerShell -- find all lines from your mod
Select-String -Path "$env:LOCALAPPDATA\DayZ\script*.log" -Pattern "MyMod" | Select-Object -Last 30

cmd

:: Command Prompt alternative
findstr "SCRIPT (E)" "%LocalAppData%\DayZ\script_2026-03-21_14-30-05.log"

Understanding Common Log Entries

Log Entry	Meaning
`SCRIPT (E): Cannot convert string to int`	Type mismatch -- passing or assigning the wrong type
`SCRIPT (E): Null pointer access in ... :: Update`	Calling a method on a NULL object (most common error)
`SCRIPT (E): Undefined variable 'manger'`	Typo in a variable name or wrong scope
`SCRIPT (E): Method 'GetHelth' not found in class 'EntityAI'`	Method does not exist -- check spelling and parent class

Real-Time Log Watching

Watch the log live in a separate PowerShell window while DayZ runs:

powershell

# Tail the latest script log in real time
Get-ChildItem "$env:LOCALAPPDATA\DayZ\script*.log" | Sort-Object LastWriteTime -Descending | Select-Object -First 1 | ForEach-Object {
    Get-Content $_.FullName -Wait -Tail 50
}

Filter to only show errors and your mod output:

powershell

Get-ChildItem "$env:LOCALAPPDATA\DayZ\script*.log" | Sort-Object LastWriteTime -Descending | Select-Object -First 1 | ForEach-Object {
    Get-Content $_.FullName -Wait -Tail 50 | Where-Object { $_ -match "SCRIPT \(E\)|SCRIPT \(W\)|\[MyMod\]" }
}

Print Debugging (The Reliable Method)

When you need to know what your code is doing at runtime, Print() is your primary tool. It writes a line to the script log that you can read afterward or watch in real time.

Basic Print Usage

class MyManager
{
    void Init()
    {
        Print("[MyMod] MyManager.Init() called");

        int count = LoadItems();
        Print("[MyMod] Loaded " + count.ToString() + " items");
    }
}

This produces lines in the script log like:

[MyMod] MyManager.Init() called
[MyMod] Loaded 5 items

Formatted Output

Use string concatenation to build informative messages with enough context to be useful on their own:

void ProcessPlayer(PlayerBase player)
{
    if (!player)
    {
        Print("[MyMod] ProcessPlayer: player is NULL, aborting");
        return;
    }

    string name = player.GetIdentity().GetName();
    vector pos = player.GetPosition();
    Print("[MyMod] Processing: " + name + " at " + pos.ToString());
}

Creating a Debug Logger

Instead of scattering raw Print() calls, create a toggleable logger:

class MyModDebug
{
    static bool s_Enabled = true;

    static void Log(string msg)
    {
        if (s_Enabled)
            Print("[MyMod:DEBUG] " + msg);
    }

    static void Error(string msg)
    {
        // Errors always print regardless of debug flag
        Print("[MyMod:ERROR] " + msg);
    }
}

Use it throughout your code: MyModDebug.Log("Player connected: " + name);

Using Preprocessor Defines for Debug-Only Code

Enforce Script supports #ifdef to include code only in development builds:

void Update()
{
    #ifdef DEVELOPER
    Print("[MyMod] Update tick, active items: " + m_Items.Count().ToString());
    #endif

    // Normal code here...
}

DEVELOPER is set in DayZDiag and Workbench but not in retail DayZ. DIAG_DEVELOPER is another useful define available only in diagnostic builds. Code inside these guards has zero cost in release builds.

Removing Debug Prints Before Release

If you do not use #ifdef guards, remove all Print() calls before publishing. Excessive output bloats logs, hurts server performance, and may expose internal information. A consistent prefix like [MyMod:DEBUG] makes them easy to find and remove.

DayZDiag -- The Debug Executable

DayZDiag is a special diagnostic build of DayZ with features the retail version lacks.

What Makes DayZDiag Different

Feature	Retail DayZ	DayZDiag
File patching support	No	Yes (`-filePatching`)
`DEVELOPER` define active	No	Yes
`DIAG_DEVELOPER` define active	No	Yes
Additional error detail in logs	Basic	Verbose
Admin console access	No	Yes
Script console	No	Yes
Free camera	No	Yes

How to Get DayZDiag

DayZDiag is included with DayZ Tools (not a separate download). After installing DayZ Tools from Steam, find DayZDiag_x64.exe in:

C:\Program Files (x86)\Steam\steamapps\common\DayZ Tools\Bin\

Launch Parameters

Create a batch file or shortcut with these parameters:

These examples assume the layout the official procedure uses: your source tree at P:\MyMod, packed output at P:\Mods\@MyMod\addons\. -mod= always points at the packed mod folder, never at the raw source tree -- file patching is layered on top of a packed mod, not a substitute for one. See Setting Up File Patching below for the junction that makes the loose files visible.

Client (singleplayer with server):

batch

DayZDiag_x64.exe -filePatching "-mod=P:\Mods\@MyMod" -profiles=clientprofile -server -port=2302

Client (connect to separate server):

batch

DayZDiag_x64.exe -filePatching "-mod=P:\Mods\@MyMod" -connect=127.0.0.1 -port=2302

Dedicated server:

batch

DayZDiag_x64.exe -filePatching -server "-mod=P:\Mods\@MyMod" -config=serverDZ.cfg -port=2302 -profiles=serverprofile

Key parameters:

Parameter	Purpose
`-filePatching`	Let the engine read loose source files for a loaded mod instead of only the packed PBO contents (see Setting Up File Patching)
`-mod=P:\Mods\@MyMod`	Load your packed mod. Several mods can be given at once, separated by semicolons
`-profiles=folder`	Set the profile folder for logs and configs
`-server`	Run as a local listen server (singleplayer testing)
`-connect=IP`	Connect to a server at the given IP
`-port=PORT`	Set the network port (default 2302)

When to Use DayZDiag vs Retail

During development: Always use DayZDiag. It gives you file patching, better errors, and debug tools.
Before release: Test with the retail DayZ executable to make sure everything works for players. Some behaviors differ between DayZDiag and retail (for example, #ifdef DEVELOPER code will not run in retail).

File Patching -- Edit Without Rebuilding

File patching is the single biggest time-saver in DayZ modding. Without it, every script change requires: edit file, rebuild PBO, copy PBO, restart DayZ. With file patching, you can: edit file, restart the mission. That is it.

How It Works

File patching does not replace packing -- it sits on top of it. Your mod is still loaded as a packed PBO; -filePatching lets the engine prefer a loose file over the packed copy when it can find one at the addon's own path.

The path it looks at is inside the DayZ installation folder, not the P: drive as such. You make your source tree appear there with a directory junction named after your mod's root prefix. Bohemia's own walkthrough creates it like this, for a mod whose root prefix is FirstMod:

batch

mklink /J "DayZInstallationFolder\FirstMod" "P:\FirstMod"

After that, <DayZ install>\FirstMod\Scripts\... is the same tree as P:\FirstMod\Scripts\..., and the engine can resolve FirstMod/Scripts/4_World/PlayerBase.c as a loose file.

So the cycle is:

Pack the mod once, producing P:\Mods\@MyMod\addons\*.pbo
Create the junction once: mklink /J "<DayZ install>\MyMod" "P:\MyMod"
Launch DayZDiag with -filePatching "-mod=P:\Mods\@MyMod"
Edit a .c file in your source tree and save it
Reconnect or restart the mission in-game
The engine picks up the edited script

No repack needed for that loop. The edit-test cycle goes from minutes to seconds.

Setting Up File Patching

Three things have to be in place. Missing any of them gives you no file patching and, in the third case, no usable error either.

A packed mod. Pack your source with Addon Builder into P:\Mods\@MyMod\addons\ and load it with -mod=P:\Mods\@MyMod.
A junction from the DayZ installation folder to your source tree, named after your mod's root prefix. Run this once, from a command prompt with the privileges to create links:

batch

mklink /J "C:\Program Files (x86)\Steam\steamapps\common\DayZ\MyMod" "P:\MyMod"

Then open the DayZ installation folder and confirm a MyMod entry is there and that browsing into it shows your source files. If it does not, nothing below will work.

allowFilePatching = 1; on the server you connect to. The official description of that serverDZ.cfg parameter is "enable connection of clients with -filePatching launch parameter enabled" -- without it, a client launched with -filePatching is refused. For a local diag server Bohemia's walkthrough also turns off two checks that a development build cannot satisfy:

cpp

BattlEye = 0;          // the diag executable does not run with BattlEye
verifySignatures = 0;  // unsigned development PBOs
allowFilePatching = 1; // allow clients with unpacked data to join

Then launch and iterate:

batch

DayZDiag_x64.exe -filePatching "-mod=P:\Mods\@MyMod" -server -port=2302

Edit a .c file, save, reconnect in-game -- your changes are live. Before you publish, remove -filePatching, repack every PBO, and verify the mod works without it.

What Works With File Patching

File Type	File Patching Works?
Script files (`.c`)	Yes -- reload on reconnect/mission restart
Layout files (`.layout`)	Usually -- reload on reconnect/mission restart, but not on every setup. Treat a layout that will not refresh as a repack, not as a bug in your markup; see the note below
Textures (`.edds`, `.paa`)	Yes -- reload on reconnect/mission restart
Sound files	Yes -- reload on reconnect/mission restart
`config.cpp`	Repack and relaunch. It is parsed at engine startup, so no reconnect or mission restart can pick up an edit -- and whether a loose `config.cpp` is read at all under file patching is not stated by any primary Bohemia source (see below). Repacking removes the question.
`mod.cpp`	Repack and relaunch. It is read at startup by the launcher/engine, so the same applies.
New `.c` files	If the file lands inside a directory already listed in a `files[]` entry, a reconnect or mission restart picks it up. If it needs a new `files[]` or module entry, that is a `config.cpp` edit -- repack and relaunch.

What is settled, and what is not. .c and .layout edits applying on reconnect or mission restart is the documented purpose of file patching -- Bohemia's walkthrough packs the PBO expressly "so we can create and edit scripts through file patching." config.cpp is different, and the honest answer is that it is unresolved: no primary source says whether a loose config.cpp is re-read under -filePatching, and it is parsed at engine startup either way, so nothing short of a relaunch could pick it up. Repack and relaunch after a config.cpp edit. That is correct under either reading, and it costs one extra Addon Builder run.

Layouts are the flaky case. Script and config behaviour is the same everywhere, but .layout patching has been reported broken on some builds and working on others, and this wiki says so in Chapter 2.4 too: layouts "may not load from unpacked folders on all setups". No current-build test was run for this chapter either. If a layout edit will not take, repack before you start rewriting the widget tree.

The official documentation contradicts itself on this flag. DayZ:Modding_Basics packs the PBO first and then junctions the source tree in so loose files can be read, and the allowFilePatching entry on DayZ:Server_Configuration describes it as allowing "clients with unpacked data to join". The Launch Parameters list on that same page says the opposite: "-filePatching - Ensures that only PBOs are loaded and NO unpacked data." Two of the three descriptions agree that the flag enables loose data, and the procedure only makes sense that way, so that is what this chapter documents -- but the stray bullet is in the official reference and you will run into it.

The File Patching Workflow

Here is the ideal development cycle:

0. Once: mklink /J "<DayZ install>\MyMod" "P:\MyMod"
1. Pack the PBO (needed once per config.cpp change, not per script edit)
2. Launch DayZDiag with -filePatching "-mod=P:\Mods\@MyMod"
3. Edit a .c file in your source tree
4. Save the file
5. In-game: disconnect and reconnect (or restart mission)
6. Check the script log for your changes
7. Repeat from step 3

This loop can take under 30 seconds per iteration compared to several minutes when rebuilding PBOs every time.

Workbench -- Script Editor and Debugger

Workbench is the official DayZ development environment included with DayZ Tools.

Launching and Setup

Open DayZ Tools from Steam, click Workbench
Go to File > Open Project and point it to your mod's script directory on P: drive
Workbench indexes your .c files and provides syntax awareness

Key Features

Syntax highlighting -- Keywords, types, strings, and comments are color-coded
Code completion -- Type a class name followed by a dot to see available methods
Error highlighting -- Syntax errors are underlined in red before you run anything
Script Console -- Run Enforce Script commands live:

// Print the player's position
Print(GetGame().GetPlayer().GetPosition().ToString());

// Spawn an item at your position
GetGame().GetPlayer().SpawnEntityOnGroundPos("AKM", GetGame().GetPlayer().GetPosition());

Limitations

Not a full game environment: Some APIs only work in the actual game, not in Workbench's simulation
Separate from game runtime: You still need to save files and restart the mission to see changes in-game
Incomplete mod context: Cross-mod references may show as errors even when they work in-game

"Enforce Script has no live debugging" is only half true. There is genuinely no official breakpoint/step/inspect debugger. But "no debugger" is not the same claim as "no way to iterate without a full rebuild-and-restart cycle" -- and it is worth not conflating the two when you are deciding how your dev loop should work. File Patching (above) already gives you script, texture and sound reload on reconnect without repacking, and usually layouts too. Beyond that, community tooling exists (search for DayZ script hot-reload / recompile-on-host tooling) that can push changed script files into an already-running game session without even a reconnect -- useful for iterating on UI logic and HUD layouts specifically. Whatever you use, understand its actual limit: reloading changed code is not the same as re-running startup-time logic (config parsing, OnInit), so a clean, from-scratch boot is still the only valid proof that a config-level or startup-level fix actually works.

Common Error Patterns and Solutions

Reference tables of the most common errors and how to fix them. Bookmark this section.

Script Errors

Error Message	Cause	Fix
`Null pointer access`	Calling a method on a variable that is NULL	Add a null check before use: `if (obj) { obj.DoThing(); }`
`Cannot convert X to Y`	Type mismatch in assignment or function call	Check the expected type. Use `Class.CastTo()` for safe casting.
`Undefined variable 'xyz'`	Typo in variable name or wrong scope	Check spelling. Make sure the variable is declared in the current scope.
`Method 'xyz' not found in class 'Abc'`	Calling a method that does not exist on that class	Check the class hierarchy. Look up the correct method name in the API.
`Division by zero`	Dividing by a variable that equals 0	Add a guard: `if (divisor != 0) { result = value / divisor; }`
`Stack overflow`	Infinite recursion in your code	Check for methods calling themselves without a proper exit condition.
`Type 'MyClass' not found`	The file defining MyClass is not loaded or is in a higher script layer	Check config.cpp script loading order. Lower layers cannot see higher layers.

Config Errors

Error Message	Cause	Fix
`Config parse error`	Missing semicolon, brace, or quote in config.cpp	Check config.cpp syntax carefully. Every property needs a semicolon. Every class needs opening and closing braces.
`Addon 'X' requires addon 'Y'`	Missing dependency in requiredAddons	Add the required addon to your `requiredAddons[]` array.
`Cannot find mod`	Mod folder name or path is wrong	Verify the `-mod=` parameter matches your mod folder name exactly.

Mod Loading Errors

Symptom	Cause	Fix
Mod does not appear in launcher	Missing or invalid `mod.cpp`	Check that `mod.cpp` exists in the mod root and has valid `name` and `dir` fields.
Scripts not executing	config.cpp not registering scripts	Verify `CfgMods` class in config.cpp has correct `Script` path pointing to your script config.cpp.
Mod loads but features missing	Script layer issue	Verify files are in correct layer folders (3_Game, 4_World, 5_Mission).

Runtime Issues

Symptom	Cause	Fix
RPC not received on server	Wrong RPC registration or identity mismatch	Check that RPC is registered on both client and server. Verify the RPC ID matches.
RPC not received on client	Server not sending, or client not registered	Add Print() on server side to confirm send. Check client registration code.
UI not showing	Layout path wrong or parent widget is null	Verify the `.layout` file path is correct relative to the mod. Check that the parent widget exists.
JSON config not loading	File path wrong or JSON syntax error	Check the file path. Validate JSON syntax (no trailing commas, proper quoting).
Player data not saving	Profile folder permissions or path issue	Check that the `$profile:` path is accessible and the folder exists.

Null Pointers and Safe Casting -- Detailed Examples

These two errors are so common they deserve worked examples.

Unsafe code (crashes if GetPlayer() or GetIdentity() returns NULL):

void DoSomething()
{
    PlayerBase player = PlayerBase.Cast(GetGame().GetPlayer());
    string name = player.GetIdentity().GetName();  // crash if player or identity is NULL
}

Safe code (guard every potential null):

void DoSomething()
{
    Man man = GetGame().GetPlayer();
    if (!man)
        return;

    PlayerBase player;
    if (!Class.CastTo(player, man))
        return;

    PlayerIdentity identity = player.GetIdentity();
    if (!identity)
        return;

    Print("[MyMod] Player: " + identity.GetName());
}

Safe casting pattern with Class.CastTo():

void ProcessEntity(Object obj)
{
    ItemBase item;
    if (Class.CastTo(item, obj))
    {
        item.SetQuantity(1);
    }
    else
    {
        Print("[MyMod] Object is not an ItemBase: " + obj.GetType());
    }
}

Class.CastTo() returns true on success, false on failure. Always check the return value.

Testing Workflow

DayZ modding has no automated test framework. Testing is manual: build, launch, play, observe, check logs. An efficient workflow is critical.

The Basic Testing Cycle

Edit Code --> Build PBO --> Launch DayZ --> Test In-Game --> Check Log --> Fix --> Repeat

With file patching, skip the PBO build: edit .c on P: drive, reconnect, check log. This reduces iteration from minutes to seconds.

Testing Server Mods

If your mod has server-side logic, you need a local dedicated server.

Option 1: Listen server (simplest)

Launch DayZDiag with -server to run both client and server in a single process:

batch

DayZDiag_x64.exe -filePatching "-mod=P:\Mods\@MyMod" -server -port=2302

This is the fastest way to test, but it does not perfectly replicate a dedicated server environment.

Option 2: Local dedicated server (most accurate)

Run a separate DayZDiag server process, then connect to it with a DayZDiag client:

Server:

batch

DayZDiag_x64.exe -filePatching -server "-mod=P:\Mods\@MyMod" -config=serverDZ.cfg -port=2302 -profiles=serverprofile

Client:

batch

DayZDiag_x64.exe -filePatching "-mod=P:\Mods\@MyMod" -connect=127.0.0.1 -port=2302

That serverDZ.cfg needs allowFilePatching = 1; (plus BattlEye = 0; and verifySignatures = 0; for a diag build), or the client will not be let in.

This gives you separate client and server logs, which is essential for debugging RPC communication and client-server split logic.

Testing Client-Only and Multiplayer

For client-only mods (UI, HUD), a listen server is sufficient: add -server to your launch parameters.

For multiplayer testing, you have three options:

Two instances on one machine: Run DayZDiag server + two clients with different -profiles folders
Test with a friend: Host a DayZDiag server, open firewall port 2302
Cloud server: Set up a remote dedicated server

Automating the Loop With a Build Script

Once you have done the build-launch-check cycle a few dozen times, wrap it in a small script so a single command packs your PBO, refreshes the mod folder, starts the server, and shows you only the lines that matter. The script does not need to be clever -- it just chains the steps you already run by hand.

Here is a self-contained batch file you can adapt. It packs one addon with Addon Builder (part of DayZ Tools), copies the result into the DayZ install, launches DayZDiag as a listen server, and then tails the newest script log filtered to errors, warnings, and your mod prefix:

batch

@echo off
:: build.bat -- pack, deploy, launch, and watch the log for one mod
setlocal

set MOD_SRC=P:\MyMod
set MOD_OUT=P:\Mods\@MyMod\addons
set DAYZ_DIAG=C:\Program Files (x86)\Steam\steamapps\common\DayZ Tools\Bin\DayZDiag_x64.exe
set ADDON_BUILDER=C:\Program Files (x86)\Steam\steamapps\common\DayZ Tools\Bin\AddonBuilder\AddonBuilder.exe

echo [build] Packing PBO...
"%ADDON_BUILDER%" "%MOD_SRC%\MyMod" "%MOD_OUT%" -clear -packonly || goto :error

echo [build] Launching DayZDiag listen server...
start "" "%DAYZ_DIAG%" -filePatching "-mod=P:\Mods\@MyMod" -server -port=2302 -profiles=P:\serverprofile

echo [build] Waiting for the log to appear...
timeout /t 5 >nul

:: Tail the newest script log, filtered to errors and this mod's output.
powershell -NoProfile -Command ^
  "Get-ChildItem 'P:\serverprofile\script*.log' | Sort-Object LastWriteTime -Descending | Select-Object -First 1 | ForEach-Object { Get-Content $_.FullName -Wait -Tail 50 | Where-Object { $_ -match 'SCRIPT \(E\)|SCRIPT \(W\)|\[MyMod\]' } }"

goto :eof

:error
echo [build] Packing failed -- see Addon Builder output above.
exit /b 1

Run it with a single command from a terminal:

batch

build.bat

The filtered tail at the end is the most valuable part: script logs contain output from vanilla code, the engine, and every loaded mod, so a filter that shows only SCRIPT (E), SCRIPT (W), and your [MyMod] prefix turns thousands of noisy lines into the handful you actually care about.

As your project grows you will likely rewrite this in a fuller language (Python is a common choice) so you can pack several addons, junction the mod folder instead of copying, and add subcommands such as a check mode that scans the latest log for errors without launching the game. The shape stays the same: pack, deploy, launch, watch.

In-Game Debug Tools

DayZDiag provides several in-game tools for testing. These are not available in retail builds.

Script Console

Open with the backtick key (`) or check your keybindings for "Script Console". Run Enforce Script commands live:

// Spawn an item at your position
GetGame().GetPlayer().SpawnEntityOnGroundPos("AKM", GetGame().GetPlayer().GetPosition());

// Teleport to coordinates
GetGame().GetPlayer().SetPosition("8000 0 10000");

// Print your current position
Print(GetGame().GetPlayer().GetPosition().ToString());

Free Camera

Toggle through the admin tools menu. Fly around detached from your character to inspect spawned objects, check placement, or observe AI behavior.

Object Spawning

// Spawn a zombie
GetGame().CreateObjectEx("ZmbM_HermitSkinny_Base", "8000 0 10000", ECE_PLACE_ON_SURFACE);

// Spawn a vehicle
GetGame().CreateObjectEx("OffroadHatchback", "8000 0 10000", ECE_PLACE_ON_SURFACE);

Time and Weather Manipulation

// Set to noon / midnight
GetGame().GetWorld().SetDate(2026, 6, 15, 12, 0);
GetGame().GetWorld().SetDate(2026, 6, 15, 0, 0);

// Override weather
Weather weather = GetGame().GetWeather();
weather.GetOvercast().Set(0.8, 0, 0);
weather.GetRain().Set(1.0, 0, 0);
weather.GetFog().Set(0.5, 0, 0);

Pre-Release Checklist

Before publishing to the Steam Workshop, go through every item.

1. Remove or Guard All Debug Output

Search for Print( and ensure every debug print is removed or wrapped in #ifdef DEVELOPER.

2. Test With a Clean Profile

Rename %LocalAppData%\DayZ\ to DayZ_backup and test from scratch. This catches assumptions about cached data or existing config files.

3. Test Mod Loading Order

Test your mod loaded before and after other popular mods. Check for class name collisions, RPC ID conflicts, and config.cpp overwrites.

4. Check for Memory Leaks

Watch server memory over time. Common leak causes: objects created in loops without cleanup, circular ref references (one side must be raw), arrays that grow without bounds.

5. Verify Stringtable Entries

Every #key_name referenced in code needs a matching row in stringtable.csv. Missing entries show as raw key strings in-game.

6. Test on a Dedicated Server

Listen server testing hides RPC timing issues, authority differences, and multi-client sync bugs. Always do a final test on a real dedicated server.

7. Test a Fresh Workshop Install

Unsubscribe, delete the local mod folder, resubscribe, and test. This verifies the Workshop upload is complete.

Common Mistakes

Mistakes every DayZ modder makes at least once. Learn from them.

1. Leaving Debug Prints in Release Builds

Players do not need [MyMod:DEBUG] Tick count: 14523 in their logs. Wrap in #ifdef DEVELOPER or remove entirely.

2. Testing Only in Singleplayer

Listen servers run client and server in one process, hiding RPCs that never cross the network, race conditions, authority check differences, and null identity references. Test with a separate dedicated server.

3. Not Testing With Other Mods

Your mod may conflict with CF, Expansion, or other popular mods via duplicate RPC IDs, missing super calls in overrides, or config class collisions. Test combinations before release.

4. Ignoring Warnings

SCRIPT (W) warnings often predict future crashes. A missing file warning today becomes a null pointer tomorrow.

5. Not Using File Patching

Repacking for every single-line script change wastes enormous time. Set file patching up once -- packed mod, junction, allowFilePatching = 1 -- and script edits then apply on reconnect (see above).

6. Not Checking Both Client and Server Logs

For RPC/client-server issues, the error is often on one side and the symptom on the other. Check both %LocalAppData%\DayZ\ (client) and your server's profile folder.

7. Changing config.cpp Without Restarting the Process

config.cpp is parsed at engine startup, so new classes, requiredAddons changes and CfgMods edits never arrive through a reconnect or a mission restart. Repack the PBO and relaunch the executable. File patching does not change this: it is documented for scripts, and nothing in the official reference says a loose config.cpp is re-read.

8. Wrong Script Layer

Lower layers cannot see higher layers. If 3_Game/ code references PlayerBase (defined in 4_World/), it fails:

3_Game/   -- Cannot reference 4_World or 5_Mission types
4_World/  -- Can reference 3_Game, cannot reference 5_Mission
5_Mission/-- Can reference 3_Game and 4_World

Next Steps

Set up file patching if you have not already. It is the single most impactful improvement to your development workflow.
Create a debug logger class for your mod with a consistent prefix so you can easily filter log output.
Practice reading the script log. Open it after every test session and look for errors and warnings, even if everything seemed to work. Silent errors can cause subtle bugs that surface later.
Explore Workbench. Open your mod's scripts in Workbench and try the Script Console. It takes time to get comfortable, but it pays off.
Build a test scenario. Create a saved mission or script that sets up a specific test environment (spawns items, sets time of day, teleports to a location) so you can reproduce bugs quickly.
Read Chapter 8.1 if you have not already built your first mod. Debugging is much easier when you understand the full mod structure.

Best Practices

Check the script log FIRST before changing code. Most bugs have a clear error message in the log. Changing code without reading the log leads to blind guessing and new bugs.
Use #ifdef DEVELOPER guards for all debug prints. This ensures zero performance cost in retail builds and prevents log spam for players. Reserve unguarded Print() for critical errors only.
Always check both client and server logs for RPC issues. The error is often on one side and the symptom on the other. A server-side null pointer silently drops the response, and the client just sees "no data received."
Set up file patching on day one. The edit-restart-check cycle drops from 3-5 minutes (PBO rebuild) to under 30 seconds (save and reconnect). This is the single biggest productivity improvement.
Use a consistent log prefix like [MyMod] in every Print call. Script logs contain output from vanilla code, the engine, and every loaded mod. Without a prefix, your output is invisible in the noise.

Theory vs Practice

Concept	Theory	Reality
`SCRIPT (W)` warnings	Warnings are non-fatal and can be safely ignored	Warnings often predict future crashes. A "Cannot open file" warning today becomes a null pointer crash tomorrow when code assumes the file was loaded.
Listen server testing	Good enough to verify scripts work	Listen servers hide entire categories of bugs: RPCs that never cross the network, missing authority checks, null `PlayerIdentity` on the server, and race conditions between client and server init.
File patching	Point `-mod=` at your source folder and edit anything	The mod still has to be packed and loaded as a PBO; file patching adds a loose-file path on top, resolved through a junction in the DayZ installation folder, and the server must allow it. `.c` edits then apply on reconnect, and `.layout` edits usually do. `config.cpp` does not -- repack and relaunch, since it is parsed at startup and no primary source says a loose copy is read.
Workbench debugger	Full IDE debugging experience	Workbench can syntax-check and run isolated scripts, but it does not replicate the full game environment. Many APIs return null or behave differently outside the game.

What You Learned

In this tutorial you learned:

How to find and read DayZ script logs, and what SCRIPT (E) and SCRIPT (W) markers mean
How to use Print() debugging with prefixes, formatters, and toggleable debug loggers
How to set up DayZDiag with file patching for rapid iteration
How to diagnose the most common error patterns: null pointers, type mismatches, undefined variables, and script layer violations
How to establish a reliable testing workflow from edit to verification

Next: Chapter 8.8: Building a HUD Overlay

Debugging & Testing Your Mod ​

Table of Contents ​

Introduction ​

The Script Log -- Your Best Friend ​

Where to Find Script Logs ​

What to Look For ​

How to Search Efficiently ​

Understanding Common Log Entries ​

Real-Time Log Watching ​

Print Debugging (The Reliable Method) ​

Basic Print Usage ​

Formatted Output ​

Creating a Debug Logger ​

Using Preprocessor Defines for Debug-Only Code ​

Removing Debug Prints Before Release ​

DayZDiag -- The Debug Executable ​

What Makes DayZDiag Different ​

How to Get DayZDiag ​

Launch Parameters ​

When to Use DayZDiag vs Retail ​

File Patching -- Edit Without Rebuilding ​

How It Works ​

Setting Up File Patching ​

What Works With File Patching ​

The File Patching Workflow ​

Workbench -- Script Editor and Debugger ​

Launching and Setup ​

Key Features ​

Limitations ​

Common Error Patterns and Solutions ​

Script Errors ​

Config Errors ​

Mod Loading Errors ​

Runtime Issues ​

Null Pointers and Safe Casting -- Detailed Examples ​

Testing Workflow ​

The Basic Testing Cycle ​

Testing Server Mods ​

Testing Client-Only and Multiplayer ​

Automating the Loop With a Build Script ​

In-Game Debug Tools ​

Script Console ​

Free Camera ​

Object Spawning ​

Time and Weather Manipulation ​

Pre-Release Checklist ​

1. Remove or Guard All Debug Output ​

2. Test With a Clean Profile ​

3. Test Mod Loading Order ​

4. Check for Memory Leaks ​

5. Verify Stringtable Entries ​

6. Test on a Dedicated Server ​

7. Test a Fresh Workshop Install ​

Common Mistakes ​

1. Leaving Debug Prints in Release Builds ​

2. Testing Only in Singleplayer ​

3. Not Testing With Other Mods ​

4. Ignoring Warnings ​

5. Not Using File Patching ​

6. Not Checking Both Client and Server Logs ​

7. Changing config.cpp Without Restarting the Process ​

8. Wrong Script Layer ​

Next Steps ​

Best Practices ​

Theory vs Practice ​

What You Learned ​

Debugging & Testing Your Mod

Table of Contents

Introduction

The Script Log -- Your Best Friend

Where to Find Script Logs

What to Look For

How to Search Efficiently

Understanding Common Log Entries

Real-Time Log Watching

Print Debugging (The Reliable Method)

Basic Print Usage

Formatted Output

Creating a Debug Logger

Using Preprocessor Defines for Debug-Only Code

Removing Debug Prints Before Release

DayZDiag -- The Debug Executable

What Makes DayZDiag Different

How to Get DayZDiag

Launch Parameters

When to Use DayZDiag vs Retail

File Patching -- Edit Without Rebuilding

How It Works

Setting Up File Patching

What Works With File Patching

The File Patching Workflow

Workbench -- Script Editor and Debugger

Launching and Setup

Key Features

Limitations

Common Error Patterns and Solutions

Script Errors

Config Errors

Mod Loading Errors

Runtime Issues

Null Pointers and Safe Casting -- Detailed Examples

Testing Workflow

The Basic Testing Cycle

Testing Server Mods

Testing Client-Only and Multiplayer

Automating the Loop With a Build Script

In-Game Debug Tools

Script Console

Free Camera

Object Spawning

Time and Weather Manipulation

Pre-Release Checklist

1. Remove or Guard All Debug Output

2. Test With a Clean Profile

3. Test Mod Loading Order

4. Check for Memory Leaks

5. Verify Stringtable Entries

6. Test on a Dedicated Server

7. Test a Fresh Workshop Install

Common Mistakes

1. Leaving Debug Prints in Release Builds

2. Testing Only in Singleplayer

3. Not Testing With Other Mods

4. Ignoring Warnings

5. Not Using File Patching

6. Not Checking Both Client and Server Logs

7. Changing config.cpp Without Restarting the Process

8. Wrong Script Layer

Next Steps

Best Practices

Theory vs Practice

What You Learned