Diablo II Save File Format

Diablo II stores your game character on disk as a .d2s file. This
is a binary file format that encodes all of the stats, items, name,
and other pieces of data.

Integers are stored in little endian
byte order, which is the native byte ordering on a x86 architecture Diablo II
is based on.

Header

Each .d2s file starts with a 765 byte header, after which data
is of variable length.

Hex	Byte	Length	Desc
0x00	0	4	Signature (0xaa55aa55)
0x04	4	4	Version ID
0x08	8	4	File size
0x0C	12	4	Checksum
0x10	16	4	Active Weapon
0x14	20	16	Character Name
0x24	36	1	Character Status
0x25	37	1	Character Progression
0x26	38	2	?
0x28	40	1	Character Class
0x29	41	2	?
0x2B	43	1	Level
0x2C	44	4	?
0x30	48	4	Time
0x34	52	4	?
0x38	56	64	Hotkeys
0x78	120	4	Left Mouse
0x7C	124	4	Right Mouse
0x80	128	4	Left Mouse (weapon switch)
0x84	132	4	Right Mouse (weapon switch)
0x88	136	32	Character Menu Appearance
0xA8	168	3	Difficulty
0xAB	171	4	Map
0xAF	175	2	?
0xB1	177	2	Merc dead?
0xB3	179	4	Merc seed?
0xB7	183	2	Merc Name ID
0xB9	185	2	Merc Type
0xBB	187	4	Merc Experience
0xBF	191	144	?
0x14F	335	298	Quest
0x279	633	81	Waypoint
0x2CA	714	51	NPC
0x2FD	765		Stats
			Items

Versions

File version. The following values are known:

71 is 1.00 through v1.06
87 is 1.07 or Expansion Set v1.08
89 is standard game v1.08
92 is v1.09 (both the standard game and the Expansion Set.)
96 is v1.10+

Checksum

To calculate the checksum set the value of it in the .d2s data
to be zero and iterate through all the bytes in the data calculating
a 32-bit checksum:

code in C

C
    sum = (sum << 1) + data[i];

code in JavaScript

source: https://github.com/krisives/d2s-format/issues/5

js
const fs = require("fs");
const path = require("path");
const file = path.join(process.cwd(), "path_to_save.d2s");

function calculateSum(data) {
  let sum = 0;
  for (let i = 0; i < data.length; i++) {
    let ch = data[i];
    if (i >= 12 && i < 16) {
      ch = 0;
    }
    ch += sum < 0;
    sum = (sum << 1) + ch;
  }

  return sum;
}

function littleToBigEndian(number) {
  return new DataView(
    Int32Array.of(
      new DataView(Int32Array.of(number).buffer).getUint32(0, true)
    ).buffer
  );
}

function ashex(buffer) {
  return buffer.getUint32(0, false).toString(16);
}

async function readSafeFile() {
  return await new Promise((resolve, reject) => {
    fs.readFile(file, (err, data) => {
      if (err) return reject(err);
      return resolve(data);
    });
  });
}

async function writeCheckSumToSafeFile(data) {
  return await new Promise((resolve, reject) => {
    fs.writeFile(file, data, err => {
      if (err) reject(err);
      resolve();
    });
  });
}

readSafeFile().then(data => {
  const sum = calculateSum(data);
  const bufferSum = littleToBigEndian(sum);
  const hex = ashex(bufferSum);
  const newData = data;
  for (let i = 0; i < 4; i++) {
    newData[12 + i] = bufferSum.getInt8(i);
  }
  writeCheckSumToSafeFile(newData).then(() => console.log(hex));
});

code in golang

source: https://github.com/gucio321/d2d2s/blob/66f91e2af7b3949ca7f279aae397bd8904519e2d/pkg/d2s/d2s.go#L397

golang
// CalculateChecksum calculates a checksum and saves in a byte slice 
func CalculateChecksum(data *[]byte) {
        var sum uint32
        for i := range *data {
                sum = ((sum << 1) % math.MaxUint32) | (sum >> (int32Size*byteLen - 1))

                sum += uint32((*data)[i])
        }

        sumBytes := make([]byte, int32Size)
        binary.LittleEndian.PutUint32(sumBytes, sum)

        const (
                int32Size = 4
                checksumPosition = 12
        )
        for i := 0; i < int32Size; i++ {
                (*data)[checksumPosition+i] = sumBytes[i]
        }
}

If the checksum is invalid, Diablo II will not open the save file.

Active Weapon

TODO

Character Name

Character names are store as an array of 16 characters which contain
a null terminated string padded with 0x00 for the remaining bytes.
Characters are stored as 8-bit ASCII, but remember that valid must
follow these rules:

Must be 2-15 in length
Must begin with a letter
May contain up to one hyphen (-) or underscore (_)
May contain letters

Character Status

This is a 8-bit field:

Bit	Desc
0	?
1	?
2	Hardcore
3	Died
4	?
5	Expansion
6	?
7	?

Character Progression

TODO

Character Class

ID	Class
0	Amazon
1	Sorceress
2	Necromancer
3	Paladin
4	Barbarian
5	Druid
6	Assassin

Level

This level value is visible only in character select screen
and must be the same as this in Stats section.

Hotkeys

TODO

32 byte structure which defines how the character looks in the menu
Does not change in-game look

Difficulty

3 bytes of data that indicates which of the three difficulties the character has unlocked.
Each byte is representitive of one of the difficulties. In this order:
Normal, Nightmare, and Hell.
Each byte is a bitfield structured like this:

7	6	5	4	3	2, 1, 0
Active?	Unknown	Unknown	Unknown	Unknown	Which act (0-4)?

Map

TODO

Quest

TODO

Waypoint

Waypoint data starts with 2 chars “WS” and
6 unknown bytes, always = {0x01, 0x00, 0x00, 0x00, 0x50, 0x00}

Three structures are in place for each difficulty,
at offsets 641, 665 and 689.

The contents of this structure are as follows

byte	bytesize	contents
0	2 bytes	{0x02, 0x01} Unknown purpose
2	5 bytes	Waypoint bitfield in order of least significant bit
7	17 bytes	unknown

In the waypoint bitfield, a bit value of 1 means that the waypoint is enabled
It is in an order from lowest to highest, so 0 is Rogue encampment (ACT I) etc.
The first waypoint in each difficulty is always activated.

NPC

TODO

Stats

TODO (9-bit encoding)

Items

Items are stored in lists described by this header:

Byte	Size	Desc
0	2	“JM”
2	2	Item Count

After this come N items. Each item starts with a basic 14-byte
structure. Many fields in this structure are not “byte-aligned”
and are described by their bit position and sizes.

Bit	Size	Desc
0	16	“JM” (separate from the list header)
16	4	?
20	1	Identified
21	6	?
27	1	Socketed
28	1	?
29	1	Picked up since last save
30	2	?
32	1	Ear
33	1	Starter Gear
34	3	?
37	1	Compact
38	1	Ethereal
39	1	?
40	1	Personalized
41	1	?
42	1	Runeword
43	15	?
58	3	Parent
61	4	Equipped
65	4	Column
69	3	Row
72	1	?
73	3	Stash
76	4	?
80	24	Type code (3 letters)
108		Extended Item Data

Extended Item Data

If the item is marked as Compact (bit 37 is set) no extended
item information will exist and the item is finished.

Items with extended information store bits based on information in the item header. For example, an item marked as Socketed will store an
extra 3-bit integer encoding how many sockets the item has.

	Bit	Size	Desc
	108		Sockets
			Custom Graphics
			Class Specific
			Quality
			Mods

Custom Graphics

Custom graphics are denoted by a single bit, which if
set means a 3-bit number for the graphic index follows. If the
bit is not set the 3-bits are not present.

Bit	Size	Desc
0	1	Item has custom graphics
1	3	Alternate graphic index

Class Specific

Class items like Barbarian helms or Amazon bows have special
properties specific to those kinds of items. If the first bit
is empty the remaining 11 bits will not be present.

Bit	Size	Desc
0	1	Item has class specific data
1	11	Class specific bits

Quality

Item quality is encoded as a 4-bit integer.

Low Quality

Mods

After each item is a list of mods. The list is a series of key value
pairs where the key is a 9-bit number and the value depends on the key.
The list ends when key 511 (0x1ff) is found which is all 9-bits
being set.

Using the file ItemStatCost.txt as a tab-delimited CSV file you can
extract the ID column which maps to the 9-bit keys. The columns
Save Bits and Param Bits describe how large the mod is.

The only exception is min-max style modifiers which use the next row
in the CSV to store the “max” portion of the mod. The bit sizes of
these two can be different and you should sum them to get the total
size.

Runeword

TODO

Parent

All items are located somewhere and have a “parent” which
can be another item, such as when inserting a jewel.

Value	Desc
0	Stored
1	Equipped
2	Belt
4	Cursor
6	Item

For items that are “stored” a 3-bit integer encoded starting at
bit 73 describes where to store the item:

Value	Desc
1	Inventory
4	Horadric Cube
5	Stash

Equipped

Items that are equipped describe their slot:

Value	Slot
1	Helmet
2	Amulet
3	Armor
4	Weapon (Right)
5	Weapon (Left)
6	Ring (Right)
7	Ring (Left)
8	Belt
9	Boots
10	Gloves
11	Alternate Weapon (Right)
12	Alternate Weapon (Left)

Diablo II Save File Format

Header

Versions

Checksum

Active Weapon

Character Name

Character Status

Character Progression

Character Class

Level

Hotkeys

Character Menu Appearance

Difficulty

Map

Quest

Waypoint

NPC

Stats

Items

Extended Item Data

Custom Graphics

Class Specific

Quality

Low Quality

Mods

Runeword

Parent

Equipped

Sockets