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SS13 for experienced programmers

Other related guides: Understanding SS13 code and Guide to mapping

So you know how to write programs in other languages and would like a quick guide on how to understand and code for SS13? Good, this is the guide for you. It likely doesn't contain everything that you need to know but it's a start.


  • Semicolons at the end are not mandatory,
  • Loop, proc, object, variable etc. spans are determined by indentations (similar to Python, see examples below)

is the same as


which is inturn the same as


For this project use the following layout. (This layout makes searching for variable and proc definitions easier.)

   var/a = 5
   return a + i1    
   return i1
  • This guide uses the word 'object' for any defined type (see Variable types) and the word 'obj' for derivatives of atom/obj, which are all objects which can be placed on the map.
  • This guide uses the word 'AI controlled' for behavior to do with an AI player controlling an item. The term 'Game controlled' is used when refering to behavior which the script itself determins (Usually called AI controlled creatures or NPCs)
  • All things are inherited from parent objects. If a variable is defined in /obj/item, it doesn't need to be (actually can't be) redefined in /obj/item/weapon.


Variables are very general, Byond makes no difference in the declaration of strings, integers, etc. (Similar to PHP)

Predefined variables

There is a lot of predefined variables for objects in BYOND, but the most important are:

  • src - a variable equal to the object containing the proc or verb. It is defined to have the same type as that object. (Similar to "this" in Java or C++)
  • usr - a mob variable (var/mob/usr) containing the mob of the player who executed the current verb, or whose action ultimately called the current proc. A good rule of thumb is to never put usr in a proc. If src would not be the correct choice, it is better to send another argument to your proc with the information it needs.
  • args - a list of the arguments passed to the proc or verb.
  • vars - a list of object variables. If the variable name is used as an index into the list, the value of that variable is accessed.

For more SS13 specific variables see SS13 common variable meanings

Variable definition

Basic definitions
 var/i = 4
 var/a, b, c
Complex definitions

The general syntax is var/type/variable_name = value


 var/obj/item/I = new/obj/item
 I.name = "Some item"

Datum definition and declaration of a variable of that datum type:

   var/test_variable = 0 //declaration of the test_variable var
   proc/set_as(var/i) //proc definition within the test_datum datum
     test_variable = i //set the test_variable var to the value in the argument
 var/datum/test_datum/TD = new/datum/test_datum //TD will now be a reference to a datum of type test_datum
 TD.test_variable = 4  //Byond doesn't know of private variables, so you can set any variables like this
 world << TD.test_variable //will output 4 to all connected users
 TD.set_as(10) //Will call the set_as proc in the datum with the argument 10
 TD.test_variable //will output 10 to all connected users


See the main article at Binary flags.

Bitflags are variables which use bits instead of numbers to determine conditions. The bit operators are & and |. For now, you should know that bitflag operators use the binary value of numbers to determine the result. So 13 & 3 will result in 1. (1101 & 0011 = 0001) and 13 | 3 = 15 (1101 | 0011 = 1111) see if for uses

Variable types


  • datum - ordinary object type (class in java)
  • atom - atom derives into obj, turf, mob and area
  • turf - tiles which make up the floors, walls and space on SS13
  • area - areas are grouped locations. They combine many turfs and it gives some common properties. Power, atmosphere, etc. are determined by areas
  • mob - an object with life, be it game controlled or player controlled.
  • obj - objects which can be placed on the map
  • client - a new client object is created for each connected player
  • list - a list of elements. The first element in a list called L is L[1]
  • world - this is a variable where some global variables for the entire world can be set. World's contents var contains all atoms currently in the game world.

Outputting messages

The most basic way of outputting messages is with the '<<' output operator.

 world << "Hello World!" //Outputs a message to all clients in the world
 usr << "Hello usr" //Outputs a message to only the user who is tied to the calling of the proc which contains this.
Output with variables
 var/s1 = "Hello"
 var/s2 = "World"
 var/i = 2011
 world << "[s1] [s2], this guide was written in [i]" //Returns "Hello World, this guide was written in 2011"

Determining variable types in code

The istype() proc will come in handy


 var/obj/item/weapon/W = new/obj/item/weapon/baton
   world << "It's a baton!"

The second argument is optional, if it's omitted, the variable will be checked against its declared type, like

 var/obj/item/weapon/W = new/obj/item/weapon/baton
   world << "It's a weapon!"

Standard code for getting specific arguments from variables which have a type that is a subclass of the type the current proc treats them with (see any attackby() proc for examples). Note that the example below is of a proc which is globaly defined, not tied to the object. It doesn't make much sense to do it like this but it works for the purposes of the example. /obj objects don't have the 'amount' variable, it's defined in /obj/item/stack (as ilustrated by the oversimplified definition of classes below. Also note where var/ is used and where it isn't).

   var/name = "Object"
   name = "Item"
   name = "Stack"
   var/amount = 50
     var/obj/item/stack/S = O
     return S.amount

There is another way of doing this. I'll show you that it exists but it is NOT TO BE USED.

     return O:amount

The colon operator (:) in the example above tells the byond compiler: "I know what I'm doing, so ignore the fact the object doesn't have this variable, I'll make sure it works myself." The problem is that people will revise your code and use it in ways you never planed for. This means something might eventually make the O:amount throw exceptions in the form of runtime errors. Some variables might eventually need to be removed or replaced and this is impossible when they are used with object:variable as the compiler will not throw an error when the variable is removed. The error will only become apparent after the game is ran on the live server which might cause it to crash. So just don't use this method, ever.

There are some shortcuts to istype() proc:
isarea(variable) = istype(variable, /area)
isicon(variable) = istype(variable, /icon)
ismob(variable) = istype(variable, /mob)
isobj(variable) = istype(variable, /obj)
isturf(variable) = istype(variable, /turf)
isloc(variable) = ismob(variable) || isobj(variable) || isturf(variable) || isarea(variable)

Switching between variable types in code

Byond defined:

SS13 Defined:
dd_file2list(file_path, separator)
dd_text2list(text, separator, var/list/withinList)
dd_text2List(text, separator, var/list/withinList)
dd_list2text(var/list/the_list, separator)
(Defined in code/__HELPERS/type2type.dm)

For more useful procs see
code/defines/procs/helpers.dm (Dead link)
code/game/objects/items/helper_procs.dm (Dead link)


Ifs default to checking for true if not otherwise stated. True is defined for all variable types as empty, 0 or non-existant (null).


Common variable behavior in if statements:

Variable type False when True when
String (text / ascii) "" or null Anything else
Int / Real 0 or null Anything else
datum, atom null Anything else

Logical operators

Pretty standard:

 !statement1 //NOT statement1
 (statement1) && (statement2) //statement1 AND statement2
 (statement1) || (statement2) //statement1 OR statement2
 == //equals
 != //not equal
 < (<=) //less (or equal)
 > (>=) //more (or equal)
 & //bitflag AND operator. 13 & 3 = 1 (1101 & 0011 = 0001)
 | //bitflag OR operator. 13 | 3 = 15 (1101 | 0011 = 1111)

Byond does not recognize the === (identical) operator. More operators can be found in the left menu on the reference page


Byond will cancel a loop if it reaches a certain number of iteration and give a runtime error out of fear of infinite loops. Same applies for recursions. Same as anywhere else


All loops understand the continue and break commands


All loops understand the continue and break commands

For combines the for loop and foreach loop:

For loop

 for(var/i = 1; i <= 10; i++)
   world << i //Will write (each in a new line) 1 2 3 4 5 6 7 8 9 10

For each

 for(var/obj/item/weapon/baton/B in world)  //will iterate through world.contents (which contains all atoms in the world) and only pick those which are of the given type (/obj/item/weapon/baton)
   B.name = "Smelly baton" //Will apply the new name to the baton in the current iteration loop

Do - While

The Do while operator is not commonly used in SS13 code, Byond does support it though.

 var/i = 3
   world << i--

All loops understand the continue and break commands

Defining objects

Doesn't matter if you want a datum or atom, the definition of objects is the same and simple:

 /obj/item/weapon/item1 //will nmake a new object of type obj.
   var/item_property = 5 //Will define a new variable type for all item1 objs
   name = "Testing Item" //The name var is already defined in parent objects so it is not defined here, but only assigned a new valie.
 /obj/item/weapon/item1/New() //Constructor proc
   ..() //should always be present in New() procs, see ..() for more information
   item_property = 3 //An action that is performed in the object constructor.

Procs (Methods, functions, procedures)

You're used to the standards of methods, functions and procedures, right? Well procs ignore some aspects of these. They can best be compared to Java methods, as they're tied to specific objects. They cannot be defined as static, private, public, etc. tho. You can write static methods, however the compiler will not restrict you from calling them in a non-static way or environment. Same applies for non-static methods.

 proc/proc_name(var/argument1, var/argument2)
   world << "[argument1] [argument2]"

The above would declare a global proc. If you wish to tie it to a certain level


Reference manual: .. proc

This is the same as super() in Java. It calls the parent object type's proc with the same name and same arguments.


   name = "Item"
 /obj/item/New() //New() is the proc that gets called whenever a new object of this type is created. A constructor if you will.
   src.name = "It's an item!"
   name = "Stack"
   src.name = "It's a stack!"

If you have the code from the example above and create a new object of type /obj/item/stack, it will first make the item in the game world with the name "Stack", because it's defined to be that by default. Then the New() proc will be called immedietally after. This will change the name to "It's a Stack!" but the call of the parent type's New() proc with the ..() command will then set it to "It's an item!". So in the end, the new object will be called "It's an item!". The ..() command is however very important in many cases as some things are defined only in the common parent's New() procs. In Del(), the proc which gets called prior to an object's deletion, it requires the code to get to the root Del() proc to even delete it. See examples of Del() in the code.

. = ..()
Reference manual: . var

This line can be read as: set the . variable (the return value) equal to the result of calling ..() (the parent proc).

. is a special variable that represents the return value of a proc. If control reaches the end of a proc, . is returned. Writing return with no value is like writing return .

. = ..() is used when a proc override should usually return the same thing that its parent does, for example in important system procs like Initialize or Destroy.

Important procs


This proc is called whenever a new instance of the object is created. It can have arguments if needed. It should call ..() where applicable so that parent constructors can be applied.

If you wish to create a New() proc for atoms with custom arguments, ensure the first argument is for the object's location. Example:

 obj/item/weapon/my_item/New(var/location, var/i)
   //Whatever else you need to do

To make a general object use

 new /datum/test_datum

To make an atom (which usually has a locaiton)

 new /obj/item/weapon(src.loc)

For the custom example above, the code to create a new such object would be: The 5 is just an example of a value which could be assigned to the var/i in the constructor.

 new /obj/item/weapon/my_item(src.loc, 5)

Where src is the proc owner, which contains the line above. src.loc is the locaiton of the src object.


This proc gets called before an object's delection. It MUST call ..() at the end as the actual deletion is done in the root Del() proc.

An object is deleted by using the del(O) proc with O being the object to be deleted.

attack_hand(mob/M as mob)

Whenever a user (M) clicks on the object with an empty active hand

attack_paw(mob/M as mob)

Whenever a monkey (M) clicks the object with an empty active hand

If a custom attack_paw(mob/user) proc is not written for an atom, it defaults to calling attack_hand(user)


Whenever an AI or cyborg clicks the object with an empty active hand

If a custom attack_ai(mob/user) proc is not written for an atom, it defaults to calling attack_hand(user)

attack(mob/M as mob, mob/user as mob)

When the object is used to attack mob M by mob user

attackby(obj/item/W, mob/user)

When the object is being attacked by user with W (Example: If you click on wires with wirecutters)


How the item reacts to explosions. Severity can either be 1, 2 or 3 with 1 being the most destructive.


How the item reacts to a blob (magma) attack


How the item reacts to an EMP. Severity can either be 1 or 2 with 1 being the more powerful EMP surge.

Topic(href, href_list)

This one's called when you click a link in a pop-up window. Like when you increase the output of SMES cells. The href_list variable is the important one as it's a parsed version of the arguments you add into a link. To make a link in the pop-up window, add the following line to the text you display (dat in the example):

 dat += text("<A href='?src=\ref[src];select=[i]'>[src.name]</a><br>")

Check the code for more examples of this.


This gets called for all objects on every tick. If possible, avoid it as it's processor heavy, but for some things it just can't be avoided.

SS13 common variable meanings


Datums have the smallest number of pre-defined variables. These are present in all objects in the game:

 type //The type of an object. If your object is of type /obj/item/weapon/shovel writing the following: new src.type(src.loc) will make another shovel in the same tile.
 parent_type //Parent type of /obj/item/weapon/shovel is /obj/item/weapon... seems streight-foward enough.
 tag //The tag is used to help you identify things when using several instances. It has to be set manually for each instance tho. Lazy coders and mappers resulted in not many tags being used. Instances in the map editor are sorted by tag.
 vars //List of object vars the datum has defined


These variables are shared by all areas, mobs, objs and turfs.

 contents //List of contents. Closets store their contents in this var as do all storage items. All the items on a turf are in the turf's contents var.
 density //If density is at 0, you can walk over the object, if it's set to 1, you can't.
 desc //Description. When you right-click and examine an object, this will show under the name.
 dir //Object direction. Sprites have a direction variable which can have 8 'legal' states. More info
 gender //not used
 icon //The dmi file where the sprite is saved. Must be written in single quotations (Example: 'items.dmi')
 icon_state //The name of the sprite in the dmi file. If it's not a valid name or is left blank, the sprite without a name in the dmi file will be used. If such a sprite doesn't exist it will default to being blank.
 invisibility //Invisibility is used to determine what you can and what you can't see. Check the code or wait for someone who knows how exactly this works to write it here.
 infra_luminosity //Only mecha use this
 underlays //List of images (see image() proc) which are underlayed under the current sprite
 overlays //List of images (see image() proc) which are overlayed over the current sprite
 loc //Contains a reference to the turf file where the object currently is.
 layer //A numerical variable which determins how objects are layered. Tables with a layer of 2.8 are always under most items which have a layer of 3.0. Layers go up to 20, which is reserved for HUD items.
 luminosity //How much the item will glow. Note that the picking up and dropping of luminous items needs to be specially handled. See flashlight code for an example.
 mouse_over_pointer //not used
 mouse_drag_pointer //(almost) not used
 mouse_drop_pointer //not used
 mouse_drop_zone //not used
 mouse_opacity //Used in a few places. Check the description in the reference page
 name //The name of the object which is displayed when you right click the object and in the bottom left of the screen when you hover your mouse over it.
 opacity //Whether you can see through/past it (glass, floor) when set to 0 or whether you can't (walls, mecha) when set to 1.
 pixel_x //How many pixels in the x direction should the sprite be offset from the starting set. See the APC's New() proc for an example and how fire alarms are defined on the map. pixel_x = -5 will move it 5 pixels to the left and pixel_x = 5 will move it 5 pixels to the right
 pixel_y //Same as pixel_y but in the y direction. Positive values move it to the north, negative to the south.
 pixel_z //Used in isometric maps, so it's not used in SS13
 suffix //Rarely used. See the reference page for more information
 text //How to represent the object on text clients. Not used.
 type //The type of the object
 vars //See Datum above
 verbs //The verbs you can use with the item. Verbs are the options in the right click menu.
 x //X position, read only. Set the loc variable to move it or use the inbulit functions.
 y //Y position, read only. 
 z //Z position (Which z-level it's on), read only.


 var/requires_power = 1 //Areas which are to work without an APC (Such as centcom areas) should have this at 0. All other areas should have it at 1.
 var/music = null //Music to be played when you enter the area.
 luminosity = 0 //Areas which should be lit at all times (such as space and centcom) should have this at 1 as well as the sd_lighting var at 0
 var/sd_lighting = 0 //This var determines whether dynamic lighting is to be calculated for the area's tiles. Turn this to off only for areas which have the luminosity var set to 1

Most other variables exist only for technical reasons and should not be messed with unless done through existing procs, they are defined in:

 code/game/area/Space Station 13 areas.dm


There is a huge amount of variables for mobs. Take a look at the following files:


There are also additional files for aliens, larva, facehuggers and more there, but the files above will have most of the variables you might need.


 var/m_amt = 0	// How much metal the item has. Used to determine how much metal you get when feeding it into an autolathe and how much it costs to produce it at the lathe
 var/g_amt = 0	// How much glass the item has. Used to determine how much glass you get when feeding it into an autolathe and how much it costs to produce it at the lathe
 var/w_amt = 0	// waster amounts. Not used
 var/origin_tech = null //Used by R&D to determine what research bonuses it grants. See examples in item definitions in code.
 var/reliability = 100	//Used by SOME devices to determine how reliable they are. The number represents the percentual chance for them to work properly.
 var/unacidable = 0 //universal "unacidabliness" var, objects with this set to 1 cannot be destroyed by acids.
 var/throwforce = 0 //The amount of damage applies to a target when they're hit by the item.

More variables are defined in:



Items are objs which can be picked up. They're divided into several categories according to their function.

/obj/item is defined in the following file:


It adds the following variables (Look at the file for more, but these are the more important ones):

 var/horse = null //This determins how much damage the target takes when they're attacked by the item in hand. Small items usually have it at 0, medium ones between 5 and 10, rare and powerful items around 10-15 and two-handed items at 15 and more. Syndicate items have it even higher at 40 and more.
 var/item_state = null //This it the var that determines which sprite will be used for the item from icons/mob/items_lefthand.dmi and items_righthand.dmi.
 var/damtype = "brute" //Determines what damage type the item produces.
 var/health = null //Some items use this to determine when they'll break from use or damage. Not common tho.
 var/hitsound = null //Sound that's played when you hit something with the item. Not commonly used.
 var/w_class = 3.0 //Weight class.
   // w_class = 1 means it's an item that can fit in a pocket (diskette, pen, cigarette packet)
   // w_class = 2 means the item can't fit in pockets but can fit in a box (clipboard, analyzer, cleaner)
   // w_class = 3 means the item can't fit in a box but can fit in backpacks (box, rods, metal)
   // w_class = 4 means the item can't even fit in a backpack (packpack, pickaxe, fireaxe)
   // w_class = 5 is used but not for weight classes.
 var/wielded = 0 //Used for double-handed items which can be carried in one hand but needs to be wielded by two hands before they can be used. This is determined by code when wielding and unwielding. All items should start with this at 0.
 var/twohanded = 0 ///Set this to 1 if your item is two-handed.
 flags = FPRINT | TABLEPASS //Flags


Defined in:


Machinery are objs which cannot be picked up and generally require power to operate. They have the following vars defined for all of them:

 var/use_power = 0 //Determines if and how much power the machine will use each tick.
   //use_power = 0 - no power is used
   //use_power = 1 - idle power is used
   //use_power = 2 - active power is used
 var/idle_power_usage = 0 //How many watts of power the machine will use each tick when use_power is set to 1
 var/active_power_usage = 0 //How many watts of power the machine will use each tick when use_power is set to 2
 var/power_channel = EQUIP //Determines which APC power category the device falls under. EQUIP, ENVIRON or LIGHT
 var/list/component_parts = null //A list of parts needed to construct the machine from a machine frame.


 var/intact = 1 //This determines if the turf will hide pipes, cable and such. Set to 1 to hide and to 0 to not hide them. Only pipes and wire with level set to 1 will be hidden. Set their level var to 2 to keep them from being hidden.
 var/blocks_air = 0 //Determines if the turf prevents air from passing (walls) if set to 1.

Other variables exist but they're tied to atmospherics code which is not to be touched as whenever anything is changed in it it results in a million things breaking.



Simulated floors are tiles which simulate air movement and temperature. The station is made entirely from these while centcom is made from unsimulated floors to prevent massive and unneeded lag.

 var/wet = 0 //If this it a positive number, it is wet and you'll slip on it if you run.
 var/thermite = 0 //Will be set to 1 when thermite is poured on it.
Simulated floors
 var/icon_regular_floor = "floor" //Determines what icon the steel version of the floor should have. Determined at floor creation (New() proc). If the icon_state of the floor at that point is one from the global icons_to_ignore_at_floor_init var, then this variable is assigned the value "floor". The icons_to_ignore_at_floor_init list contains broken, plating, burnt and non-steel icon_states from icons/turf/floors.dmi
 heat_capacity = 10000 //When a fire (hotspot) on the tile exceeds this number, the floor has a chance of melting. The more the number is exceeded, the higher the chance of melting.
 var/broken = 0 //This mostly only determins if you'll get the tile back when you use the crowbar
 var/burnt = 0 //This mostly only determins if you'll get the tile back when you use the crowbar
 var/obj/item/stack/tile/floor_tile = new/obj/item/stack/tile/steel //What floor tile is on the tile

Simulated floors are defined in:

Simulated walls

Doesn't really contain any special new variables.

Defined in:


Performance References

Rastaf0: https://raw.githubusercontent.com/rastaf0/-tg-station/faels/code/LIGHTING/performance_notes.txt

Hosting Hosting a serverSetting up the databaseWorking with /tg/station as an upstream repository
Contributing Guide to contributing to the gameSetting up gitDownloading the source codeReporting issuesChangelogs
Coding Understanding SS13 codeSS13 for experienced programmersCode docsCoding standardsGetting Your Pull AcceptedBinary flags‎Text FormattingMySQL
Mapping Guide to mappingMap mergerGuide to door access
Spriting Guide to spritingResolving icon conflicts
Wiki Guide to contributing to the wikiWikicode