MOO3 Save Editor

Save game editor for Master of Orion 3. Parses the binary save format and lets you scan and replace species populations on any planet.

Built to solve the Ithkul problem (Harvesters eating your population), but works as a general-purpose species replacement tool.

Features

• Scan your galaxy for any species' populations
• Replace one species with another on specific planets or galaxy-wide
• Auto-detects save folder on Linux, Windows, and macOS
• Interactive species picker or command-line flags
• Dry run mode to preview changes
• Creates .bak backups before any modification
• No dependencies beyond Python 3.10+

Quick Start

# Scan for all species populations
python3 moo3_species.py

# Replace Ithkul with Klackons on shared planets (the classic use case)
python3 moo3_replace.py

# Replace Ithkul with Darloks on a specific planet
python3 moo3_replace.py --replace-with darlok --planet "Alrisha VII"

# Turn everyone on a planet into Humans
python3 moo3_replace.py --target klackon --replace-with human --planet "Psi Tauri I"

# Preview without changing anything
python3 moo3_replace.py --dry-run

Usage: moo3_species.py

Scans a save file and reports all species populations, with emphasis on planets where Ithkul cohabit with (and are eating) other species.

python3 moo3_species.py                     # auto-detect latest save
python3 moo3_species.py path/to/save.gam    # specific save file

Usage: moo3_replace.py

Replaces one species with another. Creates a .bak backup before patching.

# Replace Ithkul (default target) with interactive species picker
python3 moo3_replace.py

# Target a specific species to replace
python3 moo3_replace.py --target klackon --replace-with human

# Only replace on specific planets
python3 moo3_replace.py --planet "Alrisha VII"
python3 moo3_replace.py --planet "Alrisha VII" --planet "Phelot II"
python3 moo3_replace.py --planet "Alrisha"          # partial match: all planets in system

# Only replace where a specific species is at risk
python3 moo3_replace.py --protect klackon            # only on planets with Klackons

# Replace ALL instances galaxy-wide
python3 moo3_replace.py --target ithkul --replace-with darlok --all

# Preview changes without modifying
python3 moo3_replace.py --dry-run

# Specify a save file
python3 moo3_replace.py path/to/save.gam

Flags

Flag	Description
--target <species>	Species to replace (default: Ithkul)
--replace-with <species>	Species to replace with (interactive if omitted)
--planet "<name>"	Only affect this planet (repeatable, partial match)
--protect <species>	Only affect planets where this species is present
--all	Replace target species galaxy-wide
--dry-run	Preview changes without modifying the save

Windows

1. Install Python 3.10+ (check "Add to PATH" during install)
2. Download/clone this repo
3. Double-click moo3_replace.py or run python moo3_replace.py in a terminal

The tool auto-detects your Steam save folder and keeps the window open on Windows.

Save File Locations

The tools auto-detect saves in common locations:

Platform	Path
Linux (Steam)	~/.steam/steam/steamapps/common/Master of Orion 3/SaveGameFiles/
Windows (Steam)	C:\Program Files (x86)\Steam\steamapps\common\Master of Orion 3\SaveGameFiles\
macOS (Steam)	~/Library/Application Support/Steam/steamapps/common/Master of Orion 3/SaveGameFiles/

AutoSave files are in the AutoSaveHistory/ subdirectory.

The Ithkul Problem

Ithkul are the Harvester species in MOO3. When they share a planet with other species, they bioharvest (eat) the other populations. This is hardcoded and cannot be turned off through diplomacy or game settings.

Ithkul appear on your planets via FLU Generator planetary specials, conquest, or migration. Once present, they'll consume your population with no in-game way to remove them selectively.

The default behavior of moo3_replace.py (no flags) targets exactly this: find Ithkul on planets shared with other species and replace them.

Species IDs

From racemodifiers.txt in the game data:

race1	Species	Type
0	Human	Humanoid (Human, Evon, Psilon)
1	Imsaeis	Etherean (Imsaeis, Eoladi)
2	Silicoid	Lithic (immune to bioharvesting)
3	Meklar	Cybernetic (Meklar, Cynoid)
4	Trilarian	Ichthytosian (Trilarian, Nommo)
5	Ithkul	Harvester - eats other populations
6	Klackon	Insecta (Klackon, Tachidi)
7	Sakkra	Saurian (Sakkra, Raas, Grendarl)
8	Darlok	Metashifter (Shapeshifter)
9	NonCorporeal	Non-corporeal beings
10	Protoplasmic	Protoplasmic
11	Plant	Plant species
12	Fungal	Fungal species
13	Avian	Avian (includes Alkari)
14	Gargantua	Giant species
15	Bulrathi	Ursoid
16	Mrrshan	Feline
17	Elerian	Telepathic humanoid
18	Gnolam	Trader species
19	Elder	Elder Civilization
20	ComBot	Combat robots

How It Works

MOO3 saves are binary files with big-endian integers, UTF-16BE strings, and a custom fixed-point number format. The format was reverse-engineered from Bhruic's MOO3 Save Editor and the game binary.

Each planet has regions, and each region has a population with a species type (race1) and sub-race/magnate (race2). The replacement tool changes race1 at region_offset+10 and sets race2 to 0 at region_offset+11.

Key format details

• Header magic: VS3RDAEH / Galaxy marker: VSYXALAG
• Custom doubles: 6-byte BE signed integer + 2-byte BE uint16 fraction
• Planet slot types: H (0x48) = 31 extra bytes, L/O = 30 extra bytes, 0xFF = empty orbit
• Special record tags stored reversed (e.g., SpFLUGen stored as neGULFpS)

License

MIT