Alien Swarm: Reactive Drop Add-On Packaging Guide

VPK Files

Add-Ons are distributed in VPK (Valve PacK) files. The simplest way to make one is to drag a folder onto vpk.exe, which comes with Alien Swarm: Reactive Drop in the bin folder (the same folder that includes Hammer and HLMV, not the folder that includes client.dll).

VPK files, including the more complicated pak01_dir.vpk that stores most of the game’s files, can be viewed and extracted with GCFScape.

If your add-on is not in a VPK (for example, during development) you may wish to add -override_vpk to your command line arguments, which will cause loose files to be used instead of files inside packages, instead of the default behavior of preferring VPKs.

All files stored in a VPK are lowercase, and there is only one dot in each file’s name. This means that CoolSword.dx90.vtx will be named coolsword.vtx inside the VPK.

Add-On File Structure

There are two files specific to add-ons: addoninfo.txt and addonimage.jpg.

All other files in an add-on replace (or in some cases described later in this document, augment) files in the reactivedrop folder. If your add-on contains a file named materials/example.vmt (for an unpacked add-on, this could be at reactivedrop/addons/MyAddon/materials/example.vmt), the game acts as if that file were located at reactivedrop/materials/example.vmt.

addoninfo.txt is a VDF file that describes your add-on.

A basic addoninfo.txt file looks like this:

	"addontitle" "Cool Mission"
	"addonauthor" "Cookie9"
	"addondescription" "Shoot guns at bugs in this cool mission!"

If your add-on intentionally overrides files from another add-on (for example, a minimap replacement), you can add an overrideaddon key with the workshop ID of the other add-on. If you override files from multiple other add-ons, you can add multiple overrideaddon keys.

There are other fields in addoninfo.txt, but they are optional or not read by the game.

addonimage.jpg is a small (256x256 pixels or smaller - it will be in memory at all times when the add-on is installed) preview image for the add-on. The preview image is optional, and the Steam Workshop preview image will be used by the game instead if your add-on is on the workshop. AddonInfo is required for the game to load your add-on.

Keep in mind that unless otherwise stated, the game will only load a file with a given name from the first installed add-on that provides it. Make sure your filenames are unique - for example, include your name or your add-on’s name in the filename.

Augmented Files

In a few rare cases, the game loads a file from all add-ons that provide it and merges them.

These files are:

Augmented files in your add-on should only contain content you added or changed. Do not include the entire contents of the file from the game, as that will cause higher memory usage and cause you to unintentionally revert changes from other add-ons.

Any filename not listed here other than addoninfo.txt and addonimage.jpg will only be loaded from one add-on. Again, make sure your filenames are unique.

Packaging an “Other” Add-On

“Other” add-ons are add-ons that do not include any missions, campaigns, or challenges. They can be model, sound, or texture replacements, unofficial translations, configuration files, asset libraries, loading screens, and so on.

Packaging an “Other” add-on is simple - you just need addoninfo.txt, the files you want to add or replace, and optionally addonimage.jpg. Put them into a folder and drag the folder onto vpk.exe, then upload your add-on from the Workshop management screen in the game.

As with anything on the Steam Community, you need to have legal permission to share the files you’re uploading. Valve has given permission to use assets from Valve games in content you share on Steam, so long as it is not misrepresented as being endorsed by Valve.

It is recommended that you rename any file you copied over from another Valve IP if you modify it, as another add-on may include an unmodified version of the same file and cause conflicts.


Challenges are VDF files located in resource/challenges.

Simple challenges change console variables (convars) when they are activated, and more complex challenges include scripts or spawn definitions as well.

For example, an add-on might include a file named resource/challenges/cookie9_slippery.txt with these contents:

	"name" "Cookie9's Slippery Floor Challenge"
	"description" "Oh no! The space janitor just washed the floors! They're all slippery!"
	"author" "Cookie9"
	"icon" "swarm/challenges/cookie9_slippery"

	// if there are no allowed_mode keys, it defaults to coop.
	"allowed_mode" "coop"
	"allowed_mode" "deathmatch"

	// adding this line causes clients to download your addon, allowing you to package models/textures/sounds/particles with it.
	"required_on_client" "1"

	// any convar can be changed by a challenge, including cheats.
	"convars" {
		"asw_marine_friction" "0.2"

This add-on would also include materials/vgui/swarm/challenges/cookie9_slippery.vmt and the texture for that material.

A more complicated version of the challenge might include files named scripts/vscript/challenge_cookie9_slippery.nut or resource/alien_selection_cookie9_slippery.txt.


Missions require an overview file, which is a VDF file located in resource/overviews with the same name as the BSP file and a .txt extension.

Mission overviews have two main parts: the minimap and the mission details.

	// These values come from cl_leveloverview when on a 1024x768 resolution.
	"pos_x" "12345"
	"pos_y" "6789"
	"scale" "10.0"

	// This texture should contain a stylized view of your map. it is used on the minimap.
	"material" "vgui/swarm/overviews/cookie9_cool_mission"
	// This texture is a fancier version of your minimap image, used in briefing.
	"briefingmaterial" "vgui/swarm/overviews/cookie9_cool_mission_briefing"

	// This section is optional and only needed if you are using minimap layering.
	// The briefing material will not be replaced by these, only the minimap.
			// Z coordinate of the marines' feet.
			"AltitudeMin" "-300"
			"AltitudeMax" "-100"

	// This determines how your mission looks in the mission chooser and during briefing.
	"missiontitle" "Cool Mission"
	"description" "Shoot guns at bugs in this cool mission!"

	// These three fields are optional but recommended.
	"author" "Cookie9"
	"website" ""
	"version" "1.0"

	// This should be a 4:3 aspect ratio image representing your mission for the mission chooser.
	"image" "swarm/missionpics/cookie9_cool_mission"

	// If your mission is not part of a campaign, this is how you add credits at the end.
	// A .txt extension is automatically added. Ignored if the mission is part of a campaign.
	"CustomCreditsFile" "script/cookie9_cool_mission_credits"

	// Tags affect how the game treats your mission.
	// These are different than the searchable Workshop tags,
	// although some tags affect the Workshop uploader.
	// This example includes all tags the game currently understands,
	// but you should only include the ones that make sense for your mission.
	// Don't include tags that the game doesn't understand,
	// as they might mean something unexpected in the future.

	// Adds your mission to the Bonus Missions tab in the mission chooser.
	// Recommended for standard missions that are not part of a campaign.
	"tag" "bonus"

	// For missions that don't have a pre-set ending point, usually used with the "points" tag.
	// Adds your mission to the Endless tab in the mission chooser.
	// Should not be used on the same mission as "bonus" or for missions in a campaign.
	// It is recommended that you tag survival missions with a pre-defined number of waves as "bonus"
	// and then add the "Survival" tag when uploading to the Workshop instead of using this tag.
	// Speedruns for missions with this tag are sorted in descending order on the leaderboard.
	"tag" "endless"

	// This tag will make your mission's leaderboard show points in descending order instead of time in ascending order.
	// Use the AddPoints input on asw_gamerules to award points to the squad.
	"tag" "points"

	// Allows your mission to upload leaderboard scores even when the mission fails. Sometimes useful with "endless".
	"tag" "upload_on_failure"

	// For Deathmatch maps. Adds your mission to the Deathmatch tab in the mission chooser.
	// Should not be part of a campaign. The map must contain an asw_deathmatch_mode entity.
	"tag" "deathmatch"


Campaigns are collections of missions that are not otherwise visible in the mission chooser with a VDF file located in resource/campaigns.

The file should have a .txt extension and have a unique name, but the name doesn’t need to match anything else in your add-on.

	"CampaignName" "Cookie9's Cool Campaign"
	"CampaignDescription" "Shoot many guns at many bugs in this cool campaign!"
	"CustomCreditsFile" "script/cookie9_cool_campaign_credits"

	// The icon that will appear in the mission chooser.
	"ChooseCampaignTexture" "swarm/campaigns/cookie9_cool_campaign"

	// These should be between 0 and 1023, but are not currently used in the game.
	// If they were, they would determine the location of the campaign on a galactic map.
	"GalaxyX" "123"
	"GalaxyY" "456"

	// These next fields determine how the campaign map looks.
	// These are safe defaults, but it is highly recommended that you make something unique for your campaign.
	"CampaignTextureName" "swarm/campaign/jacob_galacticmap"
	"CampaignTextureLayer1" "swarm/Campaign/CampaignMap_EmptyLayer"
	"CampaignTextureLayer2" "swarm/Campaign/CampaignMap_EmptyLayer"
	"CampaignTextureLayer3" "swarm/Campaign/CampaignMap_EmptyLayer"

	// Search lights appear on the campaign map. Set Searchlight*X to 0 to hide the search light.
	// Coordinates are from 0 to 1023; angles are in degrees counterclockwise from the right.
	"Searchlight1X" "217"
	"Searchlight1Y" "860"
	"Searchlight1Angle" "80"
	"Searchlight2X" "263"
	"Searchlight2Y" "751"
	"Searchlight2Angle" "100"
	"Searchlight3X" "92"
	"Searchlight3Y" "446"
	"Searchlight3Angle" "90"
	"Searchlight4X" "580"
	"Searchlight4Y" "266"
	"Searchlight4Angle" "90"

	// The first mission in a campaign file is the "starting point", only shown on the map.
		"MapName" "start_area"

		// Location coordinates are from 0 to 1023. Description is shown on the campaign map.
		"LocationX" "330"
		"LocationY" "780"
		"LocationDescription" "Atmospheric Entry"

		// The starting point should be linked to the first mission in your campaign.
		"Links" "cookie9_coolcampaign_01"

		"MissionName" "Ice Cold"

		// MapName should match the name of your bsp file.
		"MapName" "cookie9_coolcampaign_01"

		"LocationX" "525"
		"LocationY" "700"
		"LocationDescription" "Ice Cream Factory"
		"ShortBriefing" "Go to the ice cream factory."

		// DifficultyModifier changes the mission difficulty.
		// 3 is about equivalent to increasing the skill level by one tier, eg. from normal to hard.
		"DifficultyModifier" "0"

		// ThreatString is not currently used, but can be any text.
		"ThreatString" "Low"

		"AlwaysVisible" "1"
		"NeedsMoreThanOneMarine" "0"

		// Link your first mission to the starting point and to the second mission.
		"Links" "start_area cookie9_coolcampaign_02"

		"MissionName" "Unfrozen Warehouse"
		"MapName" "cookie9_coolcampaign_02"
		"LocationX" "360"
		"LocationY" "506"
		"LocationDescription" "Road Salt Storage"
		"DifficultyModifier" "0"
		"ThreatString" "Medium"
		"AlwaysVisible" "1"
		"NeedsMoreThanOneMarine" "0"

		// The short briefing is shown on the campaign transition screen.
		"ShortBriefing" "Find the salt at the salt store."

		// Missions in the middle of your campaign should link to the mission immediately before and after them.
		"Links" "cookie9_coolcampaign_01 cookie9_coolcampaign_03"

		"MissionName" "Cold Fusion"
		"MapName" "cookie9_coolcampaign_03"
		"LocationX" "820"
		"LocationY" "200"
		"LocationDescription" "Ice Cream Reactor"
		"DifficultyModifier" "0"
		"ThreatString" "High"
		"AlwaysVisible" "1"
		"NeedsMoreThanOneMarine" "0"
		"ShortBriefing" "Turn off the reactor."

		// The last mission in your campaign only has one link.
		"Links" "cookie9_coolcampaign_02"

	// The game doesn't currently understand any tags for campaigns.

Publishing an add-on on the Steam Workshop

Before you can publish an add-on on the Steam workshop, you need:

Publishing a new add-on

  1. Go to Workshop › Manage on the main menu.
  2. Select “Create New Add-On”. If this is your first time or you have cleared your settings, you may need to enter a console command, which the game will inform you of.
  3. Select “New Workshop Add-On” from your list of add-ons, then click “Edit”.
  4. Select the VPK and JPEG files for your add-on.
  5. Enter the title, tags, and description for your add-on.
  6. If you are updating an existing add-on, enter some change notes in the Change Log section. These notes are added as a post on the Change Notes tab on the Steam Workshop page for your add-on.
  7. When the form is filled out, select “Publish”. Your add-on will initially be uploaded as hidden (only visible to you, people you invite as co-authors, and admins), and you can change the visibility and description at any time on the Steam Workshop website. Tags can only easily be edited by uploading a new version of the add-on.
  8. The Steam Overlay or your browser will open to the page for your add-on. From there, you can edit the title, description, and visibility, add links to other add-ons that must also be installed for yours to work, add other players as co-authors, and add preview images or video.

Preview Screenshots

If you are uploading preview screenshots of missions, it is very important to upload them in a specific order so the stats website will display the correct image for each mission.

If your add-on contains multiple types of missions, the preview images must be sorted with campaign missions first, then bonus, endless, and finally deathmatch maps.

Campaign missions are first sorted by campaign filename in alphabetical order, then by their placement within the campaign. Other maps are in alphabetical order by their filename within their map type’s section of the list.

If you want to include multiple preview images for each mission, each mission should have the same number of preview images. The first preview image for each mission will be used by the stats website.

If you have a number of preview images on your add-on that is not a multiple of the number of missions or the preview images are not in this order, the stats website may display the wrong image for a mission’s leaderboard.