Diablo II Item Format

for Diablo II v1.13d Expansion Set: Lord of Destruction

This file was originally written by Trevin Beattie, whose site is no more (his latest version of this file is available here though).

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Introduction

Having searched the web, I found very few references to the Diablo II .d2s file format, and most of them covered the old (pre-1.08) version. Diablo II v1.09 has significantly changed the file format. I have started another page which details the layout of the major parts of the .d2s file. This document focuses specifically on the item structure — all those pieces of the file tagged "JM".

Rather than describe everything in terms of byte offsets, I'm going to define the layout as a series of variable-length bit fields. This is a critical part of the item format, because the position of many of the fields can change depending on what comes before it. If I say a certain value is a 3-bit field starting at bit position 150, for example, this translates to bits 6 and 7 of the byte 18 and bit 0 of byte 19 in the data structure. You can read an arbitrary bit field programatically using the following code (in C):

#define read_bits(start,size) \
    ((*((unsigned long *) &data[(start) / 8])
      >> ((start) & 7)) & ((1 << (size)) - 1))

Item List Header

An item list begins with the following simple header:

Your item list ends with another 4-byte structure similar to the above, except the second field is zero (i.e., { 0x4A, 0x4D, 0x00, 0x00 }).

In the Expansion Set, your hireling has his/her own item list. This list is separated from yours by the 2-character identifier "jf". This is followed by an item list header for the hireling, and then his/her items. The second item list is not terminated with the same 4-byte structure as the first; instead, it is followed by the 2-character identifier "kf".

Item Structure part 1: Simple Items

There are still many fields in the item structure which I haven't figured out yet, but I'll leave placeholders for them in case I find out what they mean in the future. All sizes are in bits unless otherwise specified.

Item Variant: Player Ears

If the item is a Player Ear, its structure is slightly different than the Simple Items above. The last two fields in the Simple Item structure are replaced by the following:

Following the end of the name, the rest of the final byte will be padded with 0's if necessary, and the Player Ear structure ends there.

Item Structure part 2: Extended Items

By "extended items" I mean any items which are not simple. Simple items are those which need no further information than that given above — such as gems, potions, and small quest items — and their structure length is fixed at 14 bytes. Everything else has an extended structure with a possibly variable length set of bit fields. First, I'll describe the part of the structure that appears to be the same for all extended items. From that point on, there will be no more "bit positions"; only "this field follows that field, if it exists".

WARNING: DATA BELOW THIS POINT MAY CONTAIN ERRORS

Ring Data

After the above data, if the item is a ring, amulet, jewel, or charm, then it has a 1 bit followed by three more bits. All other items (that I've seen) have just a single 0 bit.

Size	Contents
1	If this bit is set, the item has one of multiple pictures associated with it; the next field determines which picture a particular item uses. If this bit is 0, the next field is absent. The picture field is used for rings, amulets, jewels, and charms.
3	Picture. Optional; only present if the previous bit is 1. This field chooses the particular graphic used to display the ring.

From this point on, my information is very iffy.

Unknown Field

Low Quality Item Data

If the item is one of low quality, it has 3 more bits that give the quality details:

Size	Contents
3	Quality: 0 Crude 1 Cracked 2 Damaged 3 Low Quality I haven't recorded any instances of other values, but that doesn't mean there won't be any. Also, I'm certain the value has something to do with mods on an item's inherent (non-recorded) properties, such as weapon damage, but I haven't figured out yet what the correlation is.

Normal Item Data

Normal items have no extra quality data.

High Quality ("Superior") Item Data

If the item is one of high quality, it has 3 additional bits.

Magically Enhanced Item Data

Magically enhanced items have two 11-bit fields representing the item's prefix and suffix. Either one (but not both) may be omitted. The prefix and suffix each are used in choosing the magical enhancements for an item (although the enhancements are modifiable), and can also increase the minimum level required to use them item and affect the item's color.

Set Item Data

Size	Contents
12	Set identifier; i.e., all items which are part of the set will have the same value in this field. Since I've only identified a few set items, I'll give their ID's here: 2 Cleglaw's Brace 3 Iratha's Finery 4 Isenhart's Armory 6 Milabrega's Regalia 7 Cathan's Traps 11 Berserker's Arsenal 12 Death's Disguise 13 Angelic Raiment

Rare Item Data

This is by far the worst beast to decode. Rare items have a variable number of bits before we get to the item contents, and this number can vary anywhere from 55 to 88!

Update 3/14/2002: EUREKA!! I've finally figured out the variable fields!; See the table below.

Unique Item Data

Unique items have an additional 12 bit field, which in most cases is the unique item ID. The few exceptions are certain quest items (e.g., the Horadric Malus).

Size	Contents
12	Item identifier. Since I've only identified a few unique items, I'll give their ID's here: 13 Ume's Lament Grim Wand 31 Hellplague Long Sword 75 Wormskull Bone Helm 77 Undead Crown Crown (no, that is not a typo!) 91 Goldskin Full Plate Mail 120 Nagelring Ring (not a typo either; I checked) 123 Amulet of the Viper 125 Horadric Staff 126 Hell Forge Hammer 4095 (0xFFF) (other; probably a quest item)

Crafted Item Data

Crafted items appear to be coded exactly like rare items, having a rare name (two parts) and six optional prefixes / suffixes.

Rune Word

If the item has a rune word (indicated by bit 42 being set), there is an additional field at this point.

Personalization

The following segment is present if and only if the item is personalized (i.e., bit 40 is set). Only armor and weapons (except for quest items) can be personalized.

Unknown Field

All items have this field between the personalization (if it exists) and the item-specific data:

Item Structure part 3: Item-Specific Data

The presence of the following fields depends on the item type. Fields which are present will be stored in the order shown. Unfortunately there is no means of telling which fields are present from the item data itself; you need to look up the item type in a table to figure out whether it is a weapon, armor, or stack, and read the fields accordingly.

Armor: Defense Rating

Armor and Weapons: Durability

Even though stacked weapons don't show any durability rating in the game, they still have two 8-bit fields in the same spot. This includes bombs (exploding and gas potions). The values in such cases are very small, so I'm not sure what they mean.

Armor and (non-stacked) Weapons: Sockets

The following field is present if and only if the item is socketed (i.e., bit 27 is set).

Size	Contents
4	Number of sockets Note that even though this field is 4 bits wide, each item type has a built-in upper limit to the total number of sockets. This limit is built into the game. The most I've ever seen is 6 for, e.g., a gothic axe.

Tomes:

Tomes have an extra 5 bits inserted at this point. I have no idea what purpose they serve. It looks like the value is 0 on all of my tomes.

Stacked Weapons, Quivers, Keys, and Tomes: Quantity

Item Structure part 3: Magical Enhancements

Item Structure part 2^bis: Set Item Data Revisited

Items which are part of a set have an additional 5 bits following the item-specific data.

Following the item-specific data are a variable number of variable length bit fields describing any magical enhancements placed on the item. Each property begins with a 9-bit identifier. An identifier of 0x1FF (all 1's) indicates the end of the property list ... except in the event the item belongs to a set, in which case there will be another one or two groups of magical properties following, depending on whether the set item data (above) is 1 or 3, respectively. Also, if an item has been given a Rune Word, it appears that the Rune Word's properties begin with a 0x1FF identifier (presumably to set them apart from the item's normal properties... but I need to examine more items to be certain.)

Because the number of bits (and fields) after the 9-bit identifier varies, I do not give a field width here. Instead, check my table of magic properties for field sizes. I'm sure it's not complete, but it does have most of the common properties.

Following the last 9-bit value of 0x1FF, the rest of the final byte will be padded with 0's if necessary, and the item structure ends there. For example, if the item had 341 bits of data, the last (43^rd) byte will be 0x1F. If the item had 248 bits of data, the last (31^st) byte will be 0xFF.