Introduction to Modding

In this guide, I will show you the basics of modding Left 4 Dead 2, as well as introducing the tools you need for it and show how add-ons work inside the game files, I will try to explain as simple and easy to understand as possible.

Keep it mind that that might be more information that you should know and this does not teach you how to make an add-on immediately, I am solely making this guide based on my knowledge.

Requirements / Knowledge Assumptions

I am not trying to be rude, and they're probably not that important since most people know about this already, but I will assume that:

• You know some basic computer stuff, I would assume that you know how to modify/dragging files/folders and know basic file extensions in your C drive, for example like .txt, .exe, etc
  
• You know what .zip and .rar file extensions are (they both function the same), know how to deal with them, and you already have any software downloaded to unpack them, such as 7zip or WinRAR.
  
• You are comfortable with reading a long folder path. For example: C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\addons
  
• You know how to make a shortcut of an exe, not really necessary.

Before proceeding, please read it in order slow and carefully, I just want to let you know that if you are burnt out before following every single detail of this guide, I would suggest you stray away from this for a while, take a fresh air, do what you find relaxing, and come back whenever you are ready to continue.

And if you feel like you can't take this anymore, don't force yourself.

And to you, talented modders, If you think I add or explain anything wrong to this guide, you are free to criticize.

For now, I think it's only for windows user, because I don't use any other operating system, I don't know how that goes.

And without reading unnecessary information further, let's start this guide.

Tools

Tools that you need for modding are:

-> Left 4 Dead 2 Authoring Tools, perhaps the most important of them all, it contains text info for adding information for your add-on, model compiler, model viewer, mapping tool, and a packer tool, we are only focusing on the text info and packer tool for this guide.





You need to go to your steam library, and click games, then tick the TOOLS box, it will show tool applications to your steam library, then scroll until you find the tool application we need, install it.

-> GCFScape, for opening and taking a look for contents inside a .vpk file and extracting parts of it, you can download it on the website here[nemstools.github.io], at the time of writing this guide, the latest version should be 1.8.6.

You can either download the installer(exe) or the archive(zip), up to you.

1. As an exe, just double click the file to get it installed on your computer, you just need to follow the instruction stated.
   
   
2. As a zip, just extract the file to whatever folder path you like, inside you can use either the x86 for 32-bit CPU or the x64 for 64-bit CPU. For more information, you can read this[support.microsoft.com].

Make sure that you download .NET Framework as well, choose the one that runs app, and double click the installer to get it installed, some computers might have them installed already.

-> Crowbar, I wouldn't say it's optional, but it is highly recommended because of its functionality and features. it makes all tools from Left 4 Dead 2 Authoring Tools much easier to use and more.

You can download Crowbar here[github.com]. At the time of writing this guide, the latest version should be 0.74.
Scroll down and download the file with the .7z extension, it is basically behaves like .zip and .rar files, so extract it on any folder path that you like, it contains the exe file for you to open Crowbar.

And that's it! That's a total of 3 tools: Left 4 Dead 2 Authoring Tools, GCFScape, and Crowbar.

Don't worry if you don't understand some of the properties of each tool that I mentioned, I will explain every single one and on why Crowbar is an extremely great tool to use.

There are even more tools that you need based on what type of add-on that you are going to make, but we are not going to discuss about that, but all of the mentioned tools here should be important for any type.

The .vpk file extension and how they behave

The .vpk is a file extension that behaves like an executable .zip or .rar file that modifies Left 4 Dead 2 assets, it stands for Valve Pak, this is the main file to execute any modification to the game.

When you subscribe to any add-on in the workshop, a new .vpk file is downloaded and placed inside your game files when you open the game, it is located in C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\addons\workshop folder.


Your vpk file will show as a steam logo instead of this purple icon, don't worry, you didn't do anything wrong, I will explain down further a bit later.

As you can from the picture above, I have 4 subscribed items, because there are 4 total vpk files in the folder path, alongside with 4 jpgs (image file) which is a thumbnail of the add-on workshop for each respective vpk file (a jpg file with the same name as the vpk file is the thumbnail for that add-on workshop).

You might be wondering on what exactly that pile of numbers on the vpk file name, well it's actually not that important, it is a workshop item's file ID for the add-on which can be found on the item's link, each workshop items have a unique id and generate one if you upload it, here's a picture explanation.


Yes, It didn't look like I subscribed to it, because I was in an incognito tab.

Every time a workshop item updates, it will overwrite the content of the vpk file, but it will not change the item's file ID unless the author reuploads it.

Anyways, the logo of the vpk will be a steam logo at first (bear with me!), and you don't need to panic, you can actually double click on the file (don't do it now!), what it does is duplicate/copy the vpk file and place it in C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\addons folder, it is one folder up from my previous mentioned folder path, this folder path is another place to put your vpk files and it will be executed by the game as well just like what I show in this picture below which is my folder (ignore the metamod and sourcemod folder.)

Differences between these 2 folders

You might be asking on what exactly the difference between the two folder paths, I mean, both folder paths can be used to execute vpk files, right? Here's the difference,

let the first folder path I mentioned be A (C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\addons\workshop), and the other one is B (C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\addons).:

Originally posted by Interneted:

• A -> C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\addons\workshop
  
• B -> C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\addons

• vpk files that are located in A are downloaded from the workshop, you cannot put any created vpk files in A, I mean you can but it will not do anything, it will only execute add-on directly subscribed from the workshop, as for B, it will execute any vpk files being manually placed in B, you can either copy/move any vpk files from the workshop/A or any vpk files downloaded from GameMaps.
  
  
• You know that sometimes the game will have to load your add-ons, illustrated by the spinning Left 4 Dead 2 logo near your add-ons button, and you have to wait for it to finish? Yeah, it is checking for updates for every single add-ons that you subscribed from the workshop which is in A. As for B, it will load up immediately upon starting the game, but it will not update any vpks if you manually place your vpk from A or any folder to B, I mostly use B for testing my created add-ons. By the way, if you rename, delete, or move your vpk from A to another location while still subscribing to the dedicated vpk, it will download and generate a new vpk with the add-on id as its name in A upon starting the game, as well as the jpg if you modify it as well.
  
  
• You can rename your vpk file name to anything you want in B, and you can only keep executable vpks with their name being the add-on ID in A (only if you are subscribed to it, otherwise it won't do anything and will probably delete itself upon starting the game), Keep it mind that renaming your vpk file in B does not show as that add-on name in game, I will explain it later.

There are more differences to these 2 folders, which I will explain more deep down this guide.

I will make this quote and use it throughout my guide to ensure that you can recall my assumptions, since I am not going to write the same long folder path again and again.

Originally posted by Interneted:

• A -> C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\addons\workshop
  
• B -> C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\addons

GCFScape and the contents of a vpk

That is enough rambling about how vpk behave inside the game's folder, now let's take a look inside a vpk AKA opening the vpk file.

Originally posted by Interneted:

• A -> C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\addons\workshop
  
• B -> C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\addons

This is where GCFScape comes into the play, it is used to view contents of a vpk file, and extract it. For this guide I am going to use this add-on's vpk as an example, by subscribing to the add-on, load up my game, let it download, close the game, unsubscribe the add-on (it will only delete the vpk if you load up the game again), take the vpk from A, and move it to my work folder.


Now, in order to open the vpk with GCFScape, you need to right click your vpk, click open with, then select open with (It might be different steps depending on your windows version).

1. Case where you downloaded the installer version, there should be GCFScape popping when you scroll up and down to try to find it, click on it and set it to always (you can change it anytime you want, but I don't think there's a reason for it.
   
2. Case where you downloaded the archive version, make sure you have extracted the archive file to where you want it to be, then click on choose an app on you PC, search throughout your C Drive to find your GCFScape file that you have extracted, click on it and set it to always.

If you done the steps correctly, your vpk file's logo will change to that purple icon I mentioned before and you should have a similar interface like this. If it displays an error, find another vpk to open, I will explain the error later.


As you can see, the contents of a vpk is similar to .zip and .rar files, it contains files that are executable to the game, I will try to explain the structure of it.

The first file of the content is a folder called 'root', and it always occupies as the first file on every vpk. Inside that root, it contains the main files for the game to execute, I will split it into 3 categories:

addoninfo.txt

This is the file that controls information about your add-on where it will show it inside your game, it acts as a txt file, inside the file, it will look something like this (for the case of the add-on that I mentioned before)

"AddonInfo"
{
	addonSteamAppID		550
	addontitle		"Ranger's Axe"
	addonversion		1.0
	addontagline		""
	addonauthor		"adasdasd"
	addonSteamGroupName	""

	addonDescription	"Huh"
}

There's a lot going around in that text, but just focus on what's going on inside the bracket symbols, the text on the left represents keys and on the right represents value for that keys, I'll only try explain some of the perhaps important ones.

1. addonSteamAppID -> This represents what source engine app that you are going to mod on, I only know 2 of these, 500 for Left 4 Dead and 550 for Left 4 Dead 2.
   
2. addontitle -> This represents the title of the add-on.
   
3. addonauthor -> This represents the author's name of the add-on.
   
4. addonDescription -> This represents the description of the add-on.

There are more keys that aren't written in that txt file, if you want to have more information which I don't recommend for now, you can have a read here.

So that's the main keys that are mostly used for displaying information, basically the simple raw txt file should look like this (at least for me), I can use it anytime as long as this original file is not edited in some way.

  "AddonInfo"
{
     addonSteamAppID         550 //L4D2 Don't Change
     addontitle              "ADDON_NAME" //Name for Addon Menu
     addonversion            1
     addonauthor             "AUTHOR_NAME"
     addonauthorSteamID      "AUTHOT_STEAM_ID" //Optional. the number of your steam profile URL
     addonDescription        "DESCRIPTION_GOES_HERE"
}

addonimage.jpg

This is perhaps an optional file to put inside your vpk file. It essentially displays the image of your add-on inside your game, I have not tried if it works with other image extension, perhaps you can give it a try?

Originally posted by Interneted:

• A -> C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\addons\workshop
  
• B -> C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\addons

Extra notes: if you put your created add-on in B, there are 2 cases that will happen

1. If you don't have addonimage.jpg in your vpk file, it will show no picture in the add-on list in game.
   
2. If you don't have addoninfo.txt or there is no addontitle key inside addoninfo.txt in your vpk file, the add-on will not show in your add-on list in game, and it will not be enabled quietly.

If your executable add-on is in A, which means that you published your add-on and subscribed to it, your workshop thumbnail and description will take over your addonimage.jpg and addoninfo.txt to show in your add-on list (It will not overwrite addonimage.jpg and addoninfo.txt inside your published add-on), that's why sometimes you don't see both files in some vpk files on the workshop.

Assets of the add-on (asset folders and its assets)

This is the main files that changes or adds modification to the game. In my mentioned add-on, there are 3 folders, which is materials, models, sound.
You might not understand it for now, but in simplicity, each of these folders control different things:

1. The materials folder controls the texture.
   
2. The models folder controls the model, view position, and animation.
   
3. The sound folder controls the sound.

If I try to open the structure of every folder it will look something like this:

Originally posted by Interneted:

• A -> C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\addons\workshop
  
• B -> C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\addons

I hope that you can read all of these folder path carefully (some files that you have might have different icon with mine, you can ignore that for now), so this might look confusing, but spoilers, the game's original assets also have its own vpk that executes to show the original game looks without any add-ons (it is neither located in A nor B), and part of the structure/folder path of the vpk actually looks similar to the picture on the left with the same file name (trust me for now), what it does is actually replaces those original assets with the assets placed inside of the vpk file above as long as they follow the same folder path. materials folder replaces the texture, models folder replaces the animation, view position, and model, etc.


That is why you often see a lot of asset replacements in the workshop, keep it mind that they could also insert additional assets to the game instead of replacement, such as script add-ons, or you could even add additional textures to be used by resource (.res) files and model files.

-------------------------------------------------------------------------------------------------------

So that covers all of the main contents inside of the vpk file, you will understand more about the assets of the add-on if I can show you the original game's vpk, so let's move on!

gameinfo.txt and pak01_dir.vpk

Congratulations! You have made halfway through this guide, this is already so much information covered up to this point, I recommend having a break for this, if you still have the spirit to continue on, go for it!

I guess there's a word limit on guide chapters, so I'll just put it here, if you want to get a certain file from a vpk, you can right click the file on GCFScape click extract and place it whatever folder you want it to be in. Keep it mind that you cannot edit files inside GCFScape, although you can still see the contents of the file, like the txt for example.

Another thing that I forgot to mention is that if you have a really long vpk file name in the addons folder, I will not get executed by the game so it will not appear in your addon list, I am not sure about the limit, but I have come across a case where my add-on won't load because of it, so make sure to limit your vpk file name, I think it is still executed under 40 characters file name. In addition, you won't be able to open, and unpack the vpk.

If there is at least 1 non-latin word in the vpk file name such as Chinese characters, etc, you won't be able to open and unpack the vpk too.

Opening the vpk file with the situations above might result in a similar error like this:

Anyways let's get back to discussing this chapter.

So there is a file called gameinfo.txt and that file controls the update of the game, if you like messing around with the game files, there is actually multiple gameinfo.txt across the game files, but the main file we are going to be focusing is located in C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2.


Try to open your file and scroll down until you find this line over here.


So the name on the right is actually the name of the update folders (left4dead2, update, etc) that each has its own vpk, and all of those folders are located in C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2, it starts executing from bottom to the top, in this case, it will start with hl2, left4dead2 (which is |gameinfo_path| because you might realize that we are in that folder where the gameinfo.txt is located!), left4dead2_dlc1, left4dead2_dlc2, left4dead2_dlc3, and update folder (which is the TLS update, where most people complain that it breaks a lot of sourcemod plugin ,.,). each of those folder have original assets to the game that gets a replacement or an addition whenever another update folder is executed, for example:

This is the old incapacitation panel image from the left4dead2 folder:














And this is the new incapacitation panel image from the left4dead2_dlc2 folder:







So how can we can actually see assets of each update folders? Well, in every update folders, there is a file called pak01_dir.vpk, let's try to find it and open one of them in left4dead2 folder using GCFScape once again.


After you open it, it will look something like this:


As you can see, this folder structure might look very familiar to you. And yes! The asset folders from the my add-on file is present in this vpk as well, which is materials, models, and sound. My add-on vpk basically replaces the assets from pak01_dir.vpk provided that they follow the same folder path inside the vpk.

Other than those asset folders, there are many more asset folders that you can modify depending on what you want!

Anyways, after a big game update, a new update folder will be created containing pak01_dir.vpk that will add and replace any assets, this is the content of pak01_dir.vpk in update folder (TLS update):


It will replace any assets provided that the file asset name has the same name and folder path in left4dead2's pak01_dir.vpk.

You might not realize it but there is also asset folders outside of the vpk that is placed inside of the update folders (some of them are not asset folders), it will also get executed by the game and follow the vpk asset rules that I mentioned earlier.

Just to remind you that not every folder in the picture above is an asset folder, like screenshots, save, etc. but most of them actually are.

Notes:

• In order to replace these assets (make the add-on) that are outside of the pak01_dir.vpk, you will still need to create the vpk file instead of just putting the asset with the folder path, folder path must also match).
  
• There are some assets that cannot be replaced when you try the usual method of creating a vpk and put it in your addons folder (B), I am not going to mention it since it is irrelevant to this guide, there is a way to bypass it though (I will tell you next, but it is optional to read).

OPTIONAL AND RISKY INFORMATION, READ AT YOUR OWN RISK

You can make another update to pretend that the game has another update coming by making a new folder and putting your vpk there. rename it to pak01_dir.vpk and adding an extra line to gameinfo.txt in the left4dead2 folder, However, this is definitely not user-friendly and it is not recommended when you are trying to learn modding for the first time. Your gameinfo.txt might look something like this.


What's the benefit of this method you may ask? Well the game will now recognizes it as an update, and you can use it in most servers, such as official versus servers. some servers that don't work include ZoneMod, CedaPug, etc, since these servers check consistency for gameinfo.txt, but there's actually a way to bypass it though, which I am not going to tell you.

END OF OPTIONAL INFORMATION

So if you are trying to find what you can want replace or add, you need to check the update folders in order starting by the left4dead2 folder up to the update folder, to make sure that you don't get outdated assets.

Left 4 Dead 2 Authoring Tools - vpk.exe

So how do you actually create a vpk?

Well, first you need to create a folder in your work folder and name it whatever you want, now you can create asset folder, and a folder path leading to the asset. In this example I am making a simple sound replacement add-on that replaces the end theme credits, perhaps the easiest example I can show, you can also put your addoninfo.txt and addonimage.jpg into your add-on folder (don't put it inside another folder!), other type of assets like texture and model requires a certain tool to modify.


Make sure that it follow the same folder path as the original game assets in pak01_dir.vpk, as well as the same asset file name and extension, in this case I have to use wav instead of any other sound extension.

This is one of the example of replacing asset that aren't located inside pak01_dir.vpk, the file name is actually the music of the end credits theme, I used a different music with the same asset file name for the add-on making, the original folder path and one of the asset file can be found in C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\sound\music\unalive folder.

After you are finished editing your file and put it your add-on folder, you will now need to pack it into a vpk, remember that I said Left 4 Dead 2 Authoring Tools is the most important tool? Yes, one of file created in your game files after you downloaded the tool, it is called vpk.exe, this tool lets you convert your add-on folder into a vpk, the file can be found in C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\bin.


You need create a shortcut and place it to wherever you want, but I recommend placing it to either your desktop or your work folder since we are going to drag your add-on folder to vpk.exe.

After dragging it, you will see that a vpk has been created with your content inside of it, you can check it with GCFScape. By the way, dragging your vpk file back to the vpk.exe unpacks them, but make sure you do it in a separate folder, since it will overwrite everything that have the same folder path and file name without giving you any warning.

Originally posted by Interneted:

• A -> C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\addons\workshop
  
• B -> C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\addons

Now you can move your vpk to B to test it in game, if it doesn't work, you can refer to my past statement.

Originally posted by Interneted:

Extra notes: if you put your created add-on in B, there are 2 cases that will happen

1. If you don't have addonimage.jpg in your vpk file, it will not show a picture in the add-on list in game.
   
2. If you don't have addoninfo.txt or there is no addontitle key inside addoninfo.txt in your vpk file, the add-on will not show in your add-on list in game, and it will not be enabled quietly.
   
3. Make sure that it follow the same folder path as the original game assets in pak01_dir.vpk in the add-on folder, as well as the same asset file name and extension.

Other than the cases I mentioned above, make sure your asset files are put in the correct folder path, or else your add-on will not work in game.

Keep it mind that this should apply to any replacement, adding additional asset to the game such as script add-ons is a bit tricky, but it is similar to method I showed you, and I will not show it in this guide because it really depends on what you are going make, as well as taking too much space and irrelevant in this guide, this is the introduction of modding after all.

Now you can upload it workshop by opening the Left 4 Dead 2 Authoring Tools on steam, click on Workshop Manager




















Now click on the + sign on the top left corner and then fill in the necessary information, and publish your add-on.








































You will notice on the preview image stated that the image will be scaled to 640x360, this results in black bars on the top and bottom, as shown in some workshop items like this, which doesn't look good.


So how do you get a great square image quality for the preview and thumbnail just like the other items in the workshop? That's where crowbar comes into the play.

Crowbar - the source engine modding tool

Lastly, I would like to introduce you to Crowbar, a source engine modding tool, which makes add-on creation much easier, it's going to be a short explanation here, so you can finally take a deep breath.

Let's try to open Crowbar through the exe file, you should set your game to Left 4 Dead 2.


After setting it up, you might notice there a lot tabs on top, don't worry about it, I will explain shortly on which tabs are useful for any type of add-on you are creating.

• Download -> This option lets you download the add-on on the steam workshop, this is useful if you want to use an add-on without waiting for updates, as well as finding the asset you want to change from the game instead of searching the asset from pak01_dir.vpk.
  
• Unpack -> This option lets you unpack a vpk file AKA extract it, nothing much more to be mentioned here, it's the same as extracting the vpk with GCFScape, you can choose on which file you want to extract.
  
  Remember that I told you that there is sometimes an error when opening a vpk file using GCFScape? Yeah, it gives an error similar to this picture below, that where you must unpack it with Crowbar.
  
• Pack -> This option is essentially the opposite of Unpack, it lets you pack your add-on folder into a vpk, it's the same as packing the folder with vpk.exe.
  
• Publish -> This option lets you publish your add-on with the necessary information you need to put in, perhaps the major difference with the Left 4 Dead 2 Authoring Tools' workshop manager is that you can publish any image without it being scaled as well as gif images for your thumbnail, and provided with a bit more interface too.

The last 4 tabs are for changing your option of your tool and checking for any updates for Crowbar, no other important information worth mentioning here.

Keep it mind that Left 4 Dead 2 Authoring Tools still needs to be installed in order for Crowbar to function properly, since Crowbar executes the files from the tool.

More information about Crowbar:
https://steamcommunity.com/sharedfiles/filedetails/?id=2283219908
Congratulations! You have made it to the end of the guide, basically that's all you need to know when starting to mod Left 4 Dead 2 according to me!

Final words

I hope you have understood on every detail that I have explained, perhaps you will have the knowledge of some modding tools on the other modding guides that mentioned it, if you think that you don't understand some parts that I am explaining, feel free to leave a comment, I will try to answer if I got some time!

This is my first guide, I am still not getting used to putting images and gifs, as well as using the text formatting, but I think it looks good for now!

I have introduced you to all the tools you need for any type of add-on you want to make, if you want to start making your own add-on, this guide covers the dedicated tools to make the type of add-on you want, as well as any guide to make it, check it out here.
https://steamcommunity.com/sharedfiles/filedetails/?id=1316254513
There are more useful tools that you can use for source engine modding can be found here, you don't actually need every single one, just use the tools you are comfortable with depending on the interfaces and the type of add-on you are making.

If you have any questions regarding modding, you can also try to ask in the Dead4Mods discord server, link to the server here[discord.com]. I will be on the server and try to help you if I can and got any spare time, though I got to be honest, some of members are a little bit rude sometimes, but hey, at least I got some answers and the least I can do for them is thank them.

Steam keeps on deleting my links, if you need them, you can let me know in the comments.

As always, Thanks for reading this far, have a great day and Happy Modding!

First release to the public in 11/06/2023

[Interneted]

Cheers, mate!

[sstudios151]

this is a rlly indepth and helpful guide. i approve

[TOMI1985]

[Interneted]

I am not sure what you are trying to state, but if you're saying that you're modifying folders inside of GCFScape, that is not possible, you can only check what's exactly inside and extract the things you want. Or if you're saying that you're trying to move a folder into another folder, you can move it like the usual way (cut paste or just dragging the folder), I am not sure about the freezing problem as I don't think I've seen anyone encountered that problem.

[Kure 'Tesum]

I having a problem with L4D Modding, everytime i move a folder into a new folder from GCFScape, my folder freezes i clicked everywhere and it closes out, but when i reopened the folder, the folder that i'm trying to put into the folder is here. Is there any fix for this? If so, please make a YouTube video on that problem