FS25 Modding Debug Guide

Overview

Systematic approach to debugging FS25 mods — reading logs, common errors, console commands, and troubleshooting techniques.

When to Use

• Mod crashes or doesn't load
• Errors in log.txt
• In-game behavior doesn't match expectations
• Performance issues

Log File Location

Platform	Path
Windows	%USERPROFILE%\Documents\My Games\FarmingSimulator2025\log.txt
macOS	~/Library/Application Support/FarmingSimulator2025/log.txt

The log is overwritten each game launch. Save it before restarting if you need to preserve it.

Reading the Log

Error Severity

Prefix	Meaning
Error:	Critical — mod won't work correctly
Warning:	Non-fatal — may cause issues
LUA call stack:	Lua error with traceback
data/ or mod path	Context for where the error occurred

Common Error Patterns

Missing node / nil index:

Error: Can't find node 'wheelRepr' in '...'

Fix: Check i3dMappings or node path. Node was renamed or removed from I3D.

Lua nil error:

Error: attempt to index a nil value
LUA call stack: ...mySpecialization.lua:42

Fix: A variable is nil — check if prerequisite specialization is loaded, or if spec_ table was initialized.

Missing file:

Error: Can't load resource '...textures/diffuse.dds'

Fix: File doesn't exist at that path. Check case sensitivity (Linux/macOS).

XML parse error:

Error: XML parse error in '...modDesc.xml' at line 15

Fix: Invalid XML — unclosed tag, wrong encoding, or special characters in attributes.

descVersion mismatch:

Warning: ModDesc version ... is not supported

Fix: Update descVersion in modDesc.xml to current version.

Specialization error:

Error: Unable to add specialization 'mySpec' ... prerequisites not met

Fix: prerequisitesPresent() returned false. Check required specializations.

Console Commands

Open console with ~ (tilde) key in-game.

Command	Purpose
gsToggleStats	Performance overlay (FPS, draw calls)
gsVehicleDebug	Vehicle debug rendering
gsFillUnitDebug	Fill unit debug info
gsAIDebug	AI worker debug visualization
gsPhysicsDebug	Physics collision shapes
gsRenderCollisions	Show collision meshes
csReloadMods	Reload script-only mods without restart
gsFieldDebug	Field ownership/state overlay

Dev Mode

Launch with -cheats flag for extra commands:

• Free camera, teleport, money cheats
• Additional debug overlays

Debugging Checklist

1. Check log.txt — always start here, errors are listed in order
2. Validate XML — malformed XML is the #1 cause of "mod doesn't load"
3. Check file paths — case-sensitive on macOS, verify all referenced files exist
4. Check modDesc.xml — correct descVersion, valid <specializations> and <vehicleTypes>
5. Test with only your mod — disable other mods to rule out conflicts
6. Compare with base game — find a similar base game asset and diff against yours
7. Add print() statements — output to log.txt for Lua debugging
8. Check i3dMappings — wrong node paths are a common source of nil errors

Performance Issues

Symptom	Likely Cause	Fix
Low FPS near mod	Too many draw calls	Merge meshes, reduce materials
Stutter on load	Large textures	Reduce resolution, add mipmaps
Physics lag	Too many collision shapes	Simplify collision meshes
Memory spike	Uncompressed textures	Use DDS compression

Network / Multiplayer Issues

• All custom events must implement readStream/writeStream
• State changes must be synced via events, not just local assignment
• Test with dedicated server + client to catch sync bugs
• dirtyFlag system controls what gets synced each tick