Save/Load Systems

JSON serialization, version migration, and PERSIST group patterns define robust data persistence.

Available Scripts

save_migration_manager.gd

Expert save file versioning with automatic migration between schema versions.

save_system_encryption.gd

AES-256 encrypted saves with compression to prevent casual save editing.

MANDATORY - For Production: Read save_migration_manager.gd before shipping to handle schema changes.

NEVER Do in Save Systems

• NEVER save without version field — Game updates, old saves break. MUST include "version": "1.0.0" + migration logic for schema changes.
• NEVER use absolute paths — FileAccess.open("C:/Users/...") breaks on other machines. Use user:// protocol (maps to OS-specific app data folder).
• NEVER save Node references — save_data["player"] = $Player? Nodes aren't serializable. Extract data via player.save_data() method instead.
• NEVER forget to close FileAccess — var file = FileAccess.open(...) without .close()? File handle leak = save corruption. Use close() OR GDScript auto-close on scope exit.
• NEVER use JSON for large binary data — 10MB texture as base64 in JSON? Massive file size + slow parse. Use binary format (store_var) OR separate asset files.
• NEVER trust loaded data — Save file edited by user? data.get("health", 100) prevents crash if field missing. VALIDATE all loaded values.
• NEVER save during physics/animation frames — _physics_process trigger save? File corruption if game crashes mid-write. Save ONLY on explicit events (level complete, menu).

Pattern 1: JSON Save System (Recommended for Most Games)

Step 1: Create SaveManager AutoLoad

# save_manager.gd
extends Node

const SAVE_PATH := "user://savegame.save"

## Save data to JSON file
func save_game(data: Dictionary) -> void:
    var save_file := FileAccess.open(SAVE_PATH, FileAccess.WRITE)
    if save_file == null:
        push_error("Failed to open save file: " + str(FileAccess.get_open_error()))
        return
    
    var json_string := JSON.stringify(data, "\t")  # Pretty print
    save_file.store_line(json_string)
    save_file.close()
    print("Game saved successfully")

## Load data from JSON file
func load_game() -> Dictionary:
    if not FileAccess.file_exists(SAVE_PATH):
        push_warning("Save file does not exist")
        return {}
    
    var save_file := FileAccess.open(SAVE_PATH, FileAccess.READ)
    if save_file == null:
        push_error("Failed to open save file: " + str(FileAccess.get_open_error()))
        return {}
    
    var json_string := save_file.get_as_text()
    save_file.close()
    
    var json := JSON.new()
    var parse_result := json.parse(json_string)
    if parse_result != OK:
        push_error("JSON Parse Error: " + json.get_error_message())
        return {}
    
    return json.data as Dictionary

## Delete save file
func delete_save() -> void:
    if FileAccess.file_exists(SAVE_PATH):
        DirAccess.remove_absolute(SAVE_PATH)
        print("Save file deleted")

Step 2: Save Player Data

# player.gd
extends CharacterBody2D

var health: int = 100
var score: int = 0
var level: int = 1

func save_data() -> Dictionary:
    return {
        "health": health,
        "score": score,
        "level": level,
        "position": {
            "x": global_position.x,
            "y": global_position.y
        }
    }

func load_data(data: Dictionary) -> void:
    health = data.get("health", 100)
    score = data.get("score", 0)
    level = data.get("level", 1)
    if data.has("position"):
        global_position = Vector2(
            data.position.x,
            data.position.y
        )

Step 3: Trigger Save/Load

# game_manager.gd
extends Node

func save_game_state() -> void:
    var save_data := {
        "player": $Player.save_data(),
        "timestamp": Time.get_unix_time_from_system(),
        "version": "1.0.0"
    }
    SaveManager.save_game(save_data)

func load_game_state() -> void:
    var data := SaveManager.load_game()
    if data.is_empty():
        print("No save data found, starting new game")
        return
    
    if data.has("player"):
        $Player.load_data(data.player)

Pattern 2: Binary Save System (Advanced, Faster)

For large save files or when human-readability isn't needed:

const SAVE_PATH := "user://savegame.dat"

func save_game_binary(data: Dictionary) -> void:
    var save_file := FileAccess.open(SAVE_PATH, FileAccess.WRITE)
    if save_file == null:
        return
    
    save_file.store_var(data, true)  # true = full objects
    save_file.close()

func load_game_binary() -> Dictionary:
    if not FileAccess.file_exists(SAVE_PATH):
        return {}
    
    var save_file := FileAccess.open(SAVE_PATH, FileAccess.READ)
    if save_file == null:
        return {}
    
    var data: Dictionary = save_file.get_var(true)
    save_file.close()
    return data

Pattern 3: PERSIST Group Pattern

For auto-saving nodes with the persist group:

# Add nodes to "persist" group in editor or via code:
add_to_group("persist")

# Implement save/load in each persistent node:
func save() -> Dictionary:
    return {
        "filename": get_scene_file_path(),
        "parent": get_parent().get_path(),
        "pos_x": position.x,
        "pos_y": position.y,
        # ... other data
    }

func load(data: Dictionary) -> void:
    position = Vector2(data.pos_x, data.pos_y)
    # ... load other data

# SaveManager collects all persist nodes:
func save_all_persist_nodes() -> void:
    var save_nodes := get_tree().get_nodes_in_group("persist")
    var save_dict := {}
    
    for node in save_nodes:
        if not node.has_method("save"):
            continue
        save_dict[node.name] = node.save()
    
    save_game(save_dict)

Best Practices

1. Use user:// Protocol

# ✅ Good - platform-independent
const SAVE_PATH := "user://savegame.save"

# ❌ Bad - hardcoded path
const SAVE_PATH := "C:/Users/Player/savegame.save"

user:// paths:

• Windows: %APPDATA%\Godot\app_userdata\[project_name]
• macOS: ~/Library/Application Support/Godot/app_userdata/[project_name]
• Linux: ~/.local/share/godot/app_userdata/[project_name]

2. Version Your Save Format

const SAVE_VERSION := "1.0.0"

func save_game(data: Dictionary) -> void:
    data["version"] = SAVE_VERSION
    # ... save logic

func load_game() -> Dictionary:
    var data := # ... load logic
    if data.get("version") != SAVE_VERSION:
        push_warning("Save version mismatch, migrating...")
        data = migrate_save_data(data)
    return data

3. Handle Errors Gracefully

func save_game(data: Dictionary) -> bool:
    var save_file := FileAccess.open(SAVE_PATH, FileAccess.WRITE)
    if save_file == null:
        var error := FileAccess.get_open_error()
        push_error("Save failed: " + error_string(error))
        return false
    
    save_file.store_line(JSON.stringify(data))
    save_file.close()
    return true

4. Auto-Save Pattern

var auto_save_timer: Timer

func _ready() -> void:
    # Auto-save every 5 minutes
    auto_save_timer = Timer.new()
    add_child(auto_save_timer)
    auto_save_timer.wait_time = 300.0
    auto_save_timer.timeout.connect(_on_auto_save)
    auto_save_timer.start()

func _on_auto_save() -> void:
    save_game_state()
    print("Auto-saved")

Testing Save Systems

func _ready() -> void:
    if OS.is_debug_build():
        test_save_load()

func test_save_load() -> void:
    var test_data := {"test_key": "test_value", "number": 42}
    save_game(test_data)
    var loaded := load_game()
    assert(loaded.test_key == "test_value")
    assert(loaded.number == 42)
    print("Save/Load test passed")

Common Gotchas

Issue: Saved Vector2/Vector3 not loading correctly

# ✅ Solution: Store as x, y, z components
"position": {"x": pos.x, "y": pos.y}

# Then reconstruct:
position = Vector2(data.position.x, data.position.y)

Issue: Resource paths not resolving

# ✅ Store resource paths as strings
"texture_path": texture.resource_path

# Then reload:
texture = load(data.texture_path)

Reference

• Godot Docs: Saving Games
• Godot Docs: File System

Related

• Master Skill: godot-master