PRO File Format

PRO files are binary prototype records. A prototype describes the default properties of an object: its PID, art FID, name and description message id, flags, script id, material, and type-specific data such as weapon damage, critter stats, or door key codes.

Map objects and inventory entries usually store per-instance state separately. The PRO file is the shared template that the engine loads when it needs the object's base data.

Location and lookup

Prototype files are stored below proto\<type>. These paths are relative to master.dat or critter.dat when packed, or to the game's data directory when unpacked. The file name is not derived directly from the PID number at runtime; it is looked up through the matching .lst file.

Object type	PID high byte	Directory	List file	Message file
Item	0	proto\items	proto\items\items.lst	text\<language>\game\pro_item.msg
Critter	1	proto\critters	proto\critters\critters.lst	text\<language>\game\pro_crit.msg
Scenery	2	proto\scenery	proto\scenery\scenery.lst	text\<language>\game\pro_scen.msg
Wall	3	proto\walls	proto\walls\walls.lst	text\<language>\game\pro_wall.msg
Tile	4	proto\tiles	proto\tiles\tiles.lst	text\<language>\game\pro_tile.msg
Misc	5	proto\misc	proto\misc\misc.lst	text\<language>\game\pro_misc.msg

The low 24 bits of a PID are a 1-based line number in the relevant list file. For example, PID 0x02000031 has object type 2 (scenery) and list index 0x31 (49), so the engine reads line 49 from proto\scenery\scenery.lst and opens that file in proto\scenery.

When reading a list line, the engine cuts the line at the first space and then removes CR/LF. This allows comments after the filename, but it also means filenames cannot contain spaces.

Many vanilla PRO filenames follow an eight-digit decimal naming convention such as 00000032.pro, but the list file is authoritative. Tools should use the list entry rather than generating a filename from the PID.

PRO files stored inside save-game directories, for example data\savegame\slot##\proto, may be gzip-compressed like saved map objects. If a saved-game PRO does not parse as the binary format described here, try treating it as gzip data first. See Savegame Structure for how party-member PRO sidecars are copied into save slots.

Encoding and byte order

All numeric fields below are stored as big-endian 32-bit signed integers unless the table says uint8. The engine's file helpers write a 32-bit integer as high word first and high byte first.

There is no magic number or version field in a PRO file. The engine decides which structure to read from the high byte of the PID stored at the start of the file.

Type sizes

Type	Serialized size	Notes
Item	0x81, 0x7D, 0x7A, 0x51, 0x45, 0x41, or 0x3D	Depends on item subtype: armor, drug, weapon, ammo, misc, container, or key.
Critter	0x1A0 in Fallout 2, 0x19C in Fallout 1	Fallout 2 adds the native damage type at the end.
Scenery	0x31 or 0x2D	Door, stairs, and elevator have two subtype fields; ladders and generic scenery have one.
Wall	0x24	Fixed size.
Tile	0x1C	Fixed size.
Misc	0x1C	Fixed size.

Common header

Every PRO file starts with these three fields:

Offset	Type	Field	Description
0x00	int32	pid	Prototype id. High byte is the object type; low 24 bits are the list index.
0x04	int32	message_num	Base id in the type's pro_*.msg file.
0x08	int32	fid	Art FID. See LST File Format for the packed FID layout and FRM File Format for the art container it usually resolves to.

Prototype names and descriptions are not stored as strings in the PRO file. The engine uses message_num + 0 for the name and message_num + 1 for the description in the message file associated with the PID's object type. See MSG File Format for the message-list syntax and lookup behavior.

Shared object fields

Most object types continue with lighting, flags, extended flags, and a script id. Tiles are smaller and do not have light fields. Misc protos do not store a script id in the PRO file.

Field	Used by	Description
light_distance	Items, critters, scenery, walls, misc	Light radius emitted by the object.
light_intensity	Items, critters, scenery, walls, misc	Light intensity.
flags	All six PRO types	Main object flags.
flags_ext	All six PRO types	Extended flags. Some values control action availability.
sid	Items, critters, scenery, walls, tiles	Script id, or -1 for no script. This refers to scripts.lst.
material	Items, scenery, walls, tiles	Material type used by engine logic and editor UI.

Known shared values

Main flags

Flag	Name	Meaning
0x00000008	Flat	Rendered early, just after tiles.
0x00000010	NoBlock	Does not block the tile.
0x00000800	MultiHex	Uses more than one hex.
0x00001000	No Highlight	Does not draw the object highlight outline.
0x00004000	TransRed	Red transparency mode.
0x00008000	TransNone	Opaque transparency mode.
0x00010000	TransWall	Wall transparency mode.
0x00020000	TransGlass	Glass transparency mode.
0x00040000	TransSteam	Steam transparency mode.
0x00080000	TransEnergy	Energy transparency mode.
0x10000000	WallTransEnd	Changes wall transparency logic.
0x20000000	LightThru	Light passes through.
0x80000000	ShootThru	Projectiles can pass through.

Materials

Value	Material
0	Glass
1	Metal
2	Plastic
3	Wood
4	Dirt
5	Stone
6	Cement
7	Leather

Script ids

Script ids are stored as packed 32-bit values. 0xFFFFFFFF means no script. For normal object scripts the high byte is the script type and the low 16 bits are the line number in scripts\scripts.lst.

Script type	Value
System	0
Spatial	1
Time	2
Item	3
Critter	4

Older format notes often describe the packed form as 0x0Y00XXXX, where Y is the script type and XXXX is the script-list index. This matches the practical values used by normal item, scenery, and critter scripts.

File layouts

The following tables list the serialized field order after the common header. They intentionally describe the file order, not the in-memory C struct padding.

Item

Order	Field	Notes
1	0x000C-0x001F	light_distance, light_intensity, flags, flags_ext, sid.
2	0x0020	type. Item subtype: armor, container, drug, weapon, ammo, misc, or key.
3	0x0024-0x0037	material, size, weight, cost, inv_fid. inv_fid is the inventory art FID, or -1.
4	0x0038	field_80 (uint8). Older notes identify this as an item sound id.
5	0x0039 onward	Subtype payload. Depends on type.

Older notes split item flags_ext into lower flag bytes plus an attack-mode byte for weapons. Fallout 2 CE reads and writes it as one 32-bit flags_ext value, so this split is best treated as a UI/editor interpretation of the same four bytes.

Extended flag	Meaning
0x00000100	Big gun.
0x00000200	Two-handed weapon.
0x00000800	Can be used.
0x00001000	Can be used on another object.
0x00008000	Container can be picked up.
0x08000000	Hidden or integral item, for example natural claws or robot weapons.

Item subtype	Value	Size	Payload fields
Armor	0	0x81	ac, 7 damage resistances, 7 damage thresholds, perk, male_fid, female_fid.
Container	1	0x41	max_size, open_flags.
Drug	2	0x7D	3 affected stats, 3 immediate amounts, first duration, 3 first delayed amounts, second duration, 3 second delayed amounts, addiction chance, withdrawal effect, withdrawal onset.
Weapon	3	0x7A	Animation code, max damage, min damage, damage type, two ranges, projectile PID, minimum strength, two AP costs, critical failure type, perk, burst rounds, caliber, ammo type PID, ammo capacity, sound code byte.
Ammo	4	0x51	Caliber, quantity, AC modifier, DR modifier, damage multiplier, damage divisor.
Misc	5	0x45	Power type PID, power type, charges.
Key	6	0x3D	Key code.

Weapon attack modes are often shown in editors as two 4-bit values: 0 none, 1 punch, 2 kick, 3 swing, 4 thrust, 5 throw, 6 fire single, 7 fire burst, and 8 flame. The lower nibble is attack mode 1 and the upper nibble is attack mode 2.

Weapon animation codes select the critter weapon animation set: 0 none, 1 knife, 2 club, 3 sledgehammer, 4 spear, 5 pistol, 6 SMG, 7 rifle, 8 big gun, 9 minigun, and 10 rocket launcher.

Critter

Critter PRO files are fixed-size in normal Fallout 2 data: 0x1A0 bytes. After the common header they store:

Field group	Contents
Shared fields	light_distance, light_intensity, flags, flags_ext, sid.
Critter identity	head_fid, ai_packet, team_num.
Critter data	d.flags, 35 base stats, 35 bonus stats, 18 skills, body type, experience, kill type, native damage type.

The player character has a special built-in PID, 0x01000000. For normal critter PRO files, the high PID byte is still 1.

Critter base and bonus stat arrays each contain 35 values in engine stat order: seven SPECIAL stats, hit points, action points, armor class, unarmed damage, melee damage, carry weight, sequence, healing rate, critical chance, better criticals, seven damage thresholds, nine damage resistances, age, and gender. The skill array contains 18 values in skill order from Small Guns through Outdoorsman.

The critter kill type field selects the target table used by critical hit effects. For example, men, ghouls, robots, and deathclaws each have different critical rows for the same hit location. The player character is special: incoming criticals against gDude use a separate player critical table instead of the critter PRO kill type path.

Critter data flag	Meaning
0x00000002	Can barter.
0x00000020	Cannot be stolen from.
0x00000040	Does not drop items.
0x00000080	Cannot lose limbs.
0x00000100	Corpse does not age away.
0x00000200	Does not heal damage over time.
0x00000400	Invulnerable.
0x00000800	Leaves no dead body.
0x00001000	Special death behavior.
0x00002000	Melee attack can be used at range.
0x00004000	Cannot be knocked down.

Scenery

Order	Field	Notes
1	light_distance, light_intensity, flags, flags_ext, sid	Shared non-tile fields.
2	type	Scenery subtype.
3	material	Named field_2C in Fallout 2 CE.
4	field_34 (uint8)	Stored as one byte.
5	Subtype payload	Depends on type.

The one-byte scenery field at 0x0028 is commonly treated as a sound id by older tools. Typical sound ids include 0x21, 0x23, 0x24, and values in the range 0x30 through 0x5A.

Scenery subtype	Value	Payload fields
Door	0	open_flags, key_code.
Stairs	1	lower_tile, upper_tile.
Elevator	2	Elevator type, elevator level. The type selects the built-in or external elevator table.
Ladder up	3	One destination field.
Ladder down	4	One destination field.
Generic	5	One generic field.

For stairs and ladders, destination tile values are packed together with elevation in a single 32-bit value in the traditional documentation. Valid destination tiles are normal map tile numbers. Map-instance data can also carry destination map ids for some scenery objects, so do not assume every travel target is fully described by the PRO file alone.

Wall, tile, and misc

Type	Fields after common header	Serialized size
Wall	light_distance, light_intensity, flags, flags_ext, sid, material.	0x24
Tile	flags, flags_ext, sid, material.	0x1C
Misc	light_distance, light_intensity, flags, flags_ext.	0x1C

Older format notes split wall and scenery flags_ext into two 16-bit halves: wall-light type flags and action flags. The serialized file still contains the same four bytes as the 32-bit flags_ext field used by the CE source.

Wall-light value	Meaning
0x0000	North / South
0x0800	East / West
0x1000	North corner
0x2000	South corner
0x4000	East corner
0x8000	West corner

Action value	Meaning
0x0001	Kneel down when using.
0x0008	Use.
0x0010	Use on another object.
0x0020	Look.
0x0040	Talk.
0x0080	Pick up.

Action behavior

Several common interactions are inferred from the PID type and flags rather than from a single named field:

• An object can be used if extended flag 0x0800 is set, or if it is an item container.
• An object can be used on another object if extended flag 0x1000 is set, or if it is an item drug.
• An object can be talked to if it is a critter, or if extended flag 0x4000 is set.
• Items can normally be picked up, but item containers require extended flag 0x8000.

Editing notes

• Keep pid, list position, directory, and object type consistent. The engine uses all of them during lookup.
• Changing a PRO filename requires updating the matching proto\<type>\<type>.lst line.
• Changing message_num changes which name and description are loaded from pro_*.msg.
• Script ids refer to scripts.lst; inserting or deleting script-list lines can retarget existing protos.
• FID fields use the same packed object-art identifiers described on the LST page, and usually resolve to FRM art.

Minimal parser subset

A tool that only needs to enrich MAP objects can often get useful classifications without parsing every subtype payload. The high-value subset is:

• 0x0000-0x0014: PID, message id, FID, light radius, light intensity, and main flags.
• 0x001C: script id for items, critters, scenery, and walls.
• 0x0020: item subtype for item PRO files and scenery subtype for scenery PRO files.
• PID high-byte object types 0 through 5: item, critter, scenery, wall, tile, misc.

This subset is enough to distinguish many MAP object categories and script-bearing object kinds, but it is not enough to fully model item stats, critter combat data, scenery destinations, or other subtype-specific behavior.

Source References

• Fallout 2 CE - proto.cc
• Fallout 2 CE - proto.h
• Fallout 2 CE - proto_types.h
• Fallout 2 CE - db.cc

History

2026-05-01 - Added source-backed local documentation based on Fallout 2 CE by OpenAI

Original public documentation: https://falloutmods.fandom.com/wiki/PRO_File_Format