Skyrim Mod:Mod File Format

Mod files (Plugin files) are collections of records, which are further divided into fields.

Records generally correspond to objects (e.g., a creature, a game setting, a dialog entry), with the fine details of the object (e.g., health of a creature, a dialog entry test) being handled by the fields of the record. Records themselves are organized into groups.

At the highest grouping level, a plugin file is generally:

• A single TES4 record (plugin information).
• A collection of top groups.

Dawnguard

The following had sub-record order changes and updates. Also pre-existing or new records were added.

• LCTN, INFO, NPC_, RACE, NAVI, QUST, REFR, WRLD

New SubRecords:

• LCTN added: ACID, ACSR, ACUN, ACEC, ACEP, RCPR
• NAVI added: NVSI
• REFR added: XATR

Record Types

Type Data Object AACT Action ACHR Actor Reference ACTI Activator ADDN Addon Node ALCH Potion AMMO Ammo ANIO Animated Object APPA Apparatus (probably unused) ARMA Armature (Model) ARMO Armor ARTO Art Object ASPC Acoustic Space ASTP Association Type AVIF Actor Values/Perk Tree Graphics BOOK Book BPTD Body Part Data CAMS Camera Shot CELL Cell CLAS Class CLFM Color CLMT Climate COBJ Constructible Object (recipes) COLL Collision Layer CONT Container CPTH Camera Path CSTY Combat Style DEBR Debris DIAL Dialog Topic DLBR Dialog Branch DLVW Dialog View

Type Data Object DOBJ Default Object Manager DOOR Door DUAL Dual Cast Data (possibly unused) ECZN Encounter Zone EFSH Effect Shader ENCH Enchantment EQUP Equip Slot (flag-type values) EXPL Explosion EYES Eyes FACT Faction FLOR Flora FLST Form List (non-leveled list) FSTP Footstep FSTS Footstep Set FURN Furniture GLOB Global Variable GMST Game Setting GRAS Grass GRUP Form Group HAZD Hazard HDPT Head Part IDLE Idle Animation IDLM Idle Marker IMAD Image Space Modifier IMGS Image Space INFO Dialog Topic Info INGR Ingredient IPCT Impact Data IPDS Impact Data Set KEYM Key

Type Data Object KYWD Keyword LAND Landscape LCRT Location Reference Type LCTN Location LGTM Lighting Template LIGH Light LSCR Load Screen LTEX Land Texture LVLI Leveled Item LVLN Leveled Actor LVSP Leveled Spell MATO Material Object MATT Material Type MESG Message MGEF Magic Effect MISC Misc. Object MOVT Movement Type MSTT Movable Static MUSC Music Type MUST Music Track NAVI Navigation (master data) NAVM Nav Mesh NPC_ Actor (NPC, Creature) OTFT Outfit PACK AI Package PERK Perk PGRE Placed grenade PHZD Placed hazard PROJ Projectile QUST Quest

Type Data Object RACE Race / Creature type REFR Object Reference REGN Region (Audio/Weather) RELA Relationship REVB Reverb Parameters RFCT Visual Effect SCEN Scene SCRL Scroll SHOU Shout SLGM Soul Gem SMBN Story Manager Branch Node SMEN Story Manager Event Node SMQN Story Manager Quest Node SNCT Sound Category SNDR Sound Reference SOPM Sound Output Model SOUN Sound SPEL Spell SPGD Shader Particle Geometry STAT Static TACT Talking Activator TES4 Plugin info TREE Tree TXST Texture Set VTYP Voice Type WATR Water Type WEAP Weapon WOOP Word Of Power WRLD World Space WTHR Weather

Groups

GRUPs are collections of records, and are used to improve scanning of files to make it easier to skip over records that the reading program is not interested in. In addition to this, subgroups for WRLD and CELLS provide some useful structural information (e.g., the division of cell data into persistent and non-persistent references.)

File Format

Name	Type/Size	Info
type	char[4]	Always "GRUP"
groupSize	uint32	Size of the entire group, including the group header (24 bytes). This is in contrast to records and fields, whose sizes does not include their header sizes.
label	uint8[4]	Format depends on group type.
groupType	int32	Group type... Type Info Label Type Description 0 Top (Type) char[4] Record type 1 World Children formid Parent (WRLD) 2 Interior Cell Block long Block number 3 Interior Cell Sub-Block long Sub-block number 4 Exterior Cell Block short[2] Grid Y, X (Note the reverse order) 5 Exterior Cell Sub-Block short[2] Grid Y, X (Note the reverse order) 6 Cell Children formid Parent (CELL) 7 Topic Children formid Parent (DIAL) 8 Cell Persistent Childen formid Parent (CELL) 9 Cell Temporary Children formid Parent (CELL) 10 Cell Visible Distant Children formid Parent (CELL)
stamp	uint16	Date stamp, presumably of the last file modification. Low byte = day; high byte = number of months since December 2002 (i.e., 1 = January 2003).
unknown	uint16
version	uint16
unknown	uint16
data	uint8[groupSize-24]	Records and subgroups.

Top Groups

In Skyrim.esm, the top, or highest level groups are stored in the following order:

GMST, KYWD, LCRT, AACT, TXST, GLOB, CLAS, FACT, HDPT, HAIR, EYES, RACE, SOUN, ASPC, MGEF, SCPT, LTEX, ENCH, SPEL, SCRL, ACTI, TACT, ARMO, BOOK, CONT, DOOR, INGR, LIGH, MISC, APPA, STAT, SCOL, MSTT, PWAT, GRAS, TREE, CLDC, FLOR, FURN, WEAP, AMMO, NPC_, LVLN, KEYM, ALCH, IDLM, COBJ, PROJ, HAZD, SLGM, LVLI, WTHR, CLMT, SPGD, RFCT, REGN, NAVI, CELL, WRLD, DIAL, QUST, IDLE, PACK, CSTY, LSCR, LVSP, ANIO, WATR, EFSH, EXPL, DEBR, IMGS, IMAD, FLST, PERK, BPTD, ADDN, AVIF, CAMS, CPTH, VTYP, MATT, IPCT, IPDS, ARMA, ECZN, LCTN, MESG, RGDL, DOBJ, LGTM, MUSC, FSTP, FSTS, SMBN, SMQN, SMEN, DLBR, MUST, DLVW, WOOP, SHOU, EQUP, RELA, SCEN, ASTP, OTFT, ARTO, MATO, MOVT, HAZD, SNDR, DUAL, SNCT, SOPM, COLL, CLFM, REVB

Whether the game engine expects this order is unknown, but it's probably safer to use this order than not.

All top groups contain records matching their label (e.g., the GMST top group contains GMST records). For most top groups, only the matching record types are present. However, in the CELL, WRLD and DIAL top groups, each main record can be followed by one or more child groups which contain additional records of a different type. Unlike Oblivion, WRLD groups in Skyrim no longer contain ROAD records.

The following groups are only found in subgroups of other records:

REFR, ACHR, NAVM, PGRE, PHZD, LAND, INFO

Notes:

• 6 record types have a GRUP but have no records:CLDC, HAIR, RGDL, SCPT, SCOL, PWAT.
• There are 2 HAZD groups, the second one has no records.

Records

Name	Type/Size	Info
type	char[4]	Type
dataSize	uint32	Size of data field.
flags	uint32	Flags... Flag Meaning 0x00000001 (TES4 record only) Master (ESM) file. 0x00000020 Deleted 0x00000040 Constant / (REFR) Hidden From Local Map (Needs Confirmation: Related to shields) 0x00000080 (TES4) Localized / Is Perch / (PHZD) Turn off fire (TES4 record only) Is localized. This will make Skyrim load the .STRINGS, .DLSTRINGS, and .ILSTRINGS files associated with the mod. If this flag is not set, lstrings are treated as zstrings. 0x00000100 Must Update Anims / (REFR) Inaccessible 0x00000200 (REFR) Hidden from local map / (ACHR) Starts dead /(REFR) MotionBlurCastsShadows 0x00000400 Quest item / Persistent reference / (LSCR) Displays in Main Menu 0x00000800 Initially disabled 0x00001000 Ignored 0x00008000 Visible when distant 0x00010000 (ACTI) Random Animation Start 0x00020000 (ACTI) Dangerous / Off limits (Interior cell) Dangerous Can't be set withough Ignore Object Interaction 0x00040000 Data is compressed 0x00080000 Can't wait 0x00100000 (ACTI) Ignore Object Interaction Ignore Object Interaction Sets Dangerous Automatically 0x00800000 Is Marker 0x02000000 (ACTI) Obstacle / (REFR) No AI Acquire 0x04000000 NavMesh Gen - Filter 0x08000000 NavMesh Gen - Bounding Box 0x10000000 (FURN) Must Exit to Talk / (REFR) Reflected By Auto Water 0x20000000 (FURN/IDLM) Child Can Use / (REFR) Don't Havok Settle 0x40000000 NavMesh Gen - Ground / (REFR) NoRespawn 0x80000000 (REFR) MultiBound
id	uint32	Record (form) identifier. TES4 records have a FormId of 0.
revision	uint32	Used for revision control by the CS (only if enabled) Probably the same format as Oblivion's
version	uint16
unknown	uint16	unknown
data	uint8[dataSize]	Data For uncompressed records, this is a sequence of fields. Compressed data is the same, except that the fields are compressed using ZLIB, and stored into the data field like so... Name Type/Size Info decompSize uint32 Size of decompressed data. compData uint8[dataSize-4] Compressed collection of fields.

Fields

Name	Type/Size	Info
type	char[4]	Field type.
dataSize	uint16	Size of data field. †
data	uint8[dataSize]	Data. Format depends on record and field type.

^†If the preceding field has the type XXXX, then dataSize will be 0 and the size of the data is in fact the 32 bit quantity stored in the XXXX field. This feature is commonly used to store large navmesh fields in Skyrim.esm.

Commonly used fields and their definitions can be found here.

See Also

• Raw Data: a dump of all records/subrecords in Skyrim.esm and their associated counts/sizes.
• Raw Function Data: a dump of all script/console functions and events in TESV.exe.