Economy System

Decoupled logic for handling buy/sell exchanges between the Wallet and Inventory systems.

dynamic_price_modifier.gd

Injection pattern for applying temporary discounts or markups based on world state (e.g. Sales).

currency_label_sync.gd

Reactive UI hook for automatically updating currency displays when balances change.

loot_drop_economy_bridge.gd

Bridge node for capturing loot events and adding funds to the player's wallet.

economy_persistence_handler.gd

Expert logic for serializing financial states into secure, loadable dictionaries.

currency_pickup_effect.gd

Visual feedback controller that triggers particles or animations upon financial gain.

trade_contract_resource.gd

Advanced barter system definition for multi-item "Quid Pro Quo" transactions.

NEVER Do in Economy Systems

• NEVER use int for large-scale premium economies — Standard 32-bit integers cap at 2.1 billion. For massive quantities, use float or a custom BigInt structure [12].
• NEVER forget to implement a Buy/Sell price spread — Allowing players to sell items for the same price they bought them creates infinite money exploits [13].
• NEVER skip "Currency Sinks" — Without mandatory costs (repairs, taxes, consumables), the game economy will suffer from hyper-inflation [14].
• NEVER perform currency validation only on the client — In multiplayer or persistent games, the server MUST be the source of truth for all financial transactions [15].
• NEVER hardcode loot drop percentages inside scripts — Changing drop rates should not require a recompile. Use Resources or outside data files for easy balancing [16].
• NEVER allow negative balances via underflow — Always check if current >= amount BEFORE subtracting. Negative gold can break logic and save files.
• NEVER modify the wallet balance directly from the UI — The UI should only request a transaction. The WalletManager should decide if it's valid and update the state.
• NEVER use floating point math for exact currency counts — 0.1 + 0.2 might equal 0.30000000000000004, leading to discrepancies. Use int for cents/smallest units.
• NEVER ignore "Transaction Logs" in serious RPGs — If money disappears, you need a history of events to debug whether it was a bug or a legitimate game event.
• NEVER give rewards without checking "Max Limit" — If a player is capped at 999,999 gold, adding 1,000 should result in 999,999, not a wrapped negative number.

Currency Manager

# economy_manager.gd (AutoLoad)
extends Node

signal currency_changed(old_amount: int, new_amount: int)

var gold: int = 0

func add_currency(amount: int) -> void:
    var old := gold
    gold += amount
    currency_changed.emit(old, gold)

func spend_currency(amount: int) -> bool:
    if gold < amount:
        return false
    
    var old := gold
    gold -= amount
    currency_changed.emit(old, gold)
    return true

func has_currency(amount: int) -> bool:
    return gold >= amount

Shop System

# shop_item.gd
class_name ShopItem
extends Resource

@export var item: Item
@export var buy_price: int
@export var sell_price: int
@export var stock: int = -1  # -1 = infinite

func can_buy() -> bool:
    return stock != 0

# shop.gd
class_name Shop
extends Resource

@export var shop_name: String
@export var items: Array[ShopItem] = []

func buy_item(shop_item: ShopItem, inventory: Inventory) -> bool:
    if not shop_item.can_buy():
        return false
    
    if not EconomyManager.has_currency(shop_item.buy_price):
        return false
    
    if not EconomyManager.spend_currency(shop_item.buy_price):
        return false
    
    inventory.add_item(shop_item.item, 1)
    
    if shop_item.stock > 0:
        shop_item.stock -= 1
    
    return true

func sell_item(item: Item, inventory: Inventory) -> bool:
    # Find matching shop item for sell price
    var shop_item := get_shop_item_for(item)
    if not shop_item:
        return false
    
    if not inventory.has_item(item, 1):
        return false
    
    inventory.remove_item(item, 1)
    EconomyManager.add_currency(shop_item.sell_price)
    return true

func get_shop_item_for(item: Item) -> ShopItem:
    for shop_item in items:
        if shop_item.item == item:
            return shop_item
    return null

Pricing Formula

func calculate_sell_price(buy_price: int, markup: float = 0.5) -> int:
    # Sell for 50% of buy price
    return int(buy_price * markup)

func calculate_dynamic_price(base_price: int, demand: float) -> int:
    # Price increases with demand
    return int(base_price * (1.0 + demand))

Loot Tables

# loot_table.gd
class_name LootTable
extends Resource

@export var drops: Array[LootDrop] = []

func roll_loot() -> Array[Item]:
    var items: Array[Item] = []
    
    for drop in drops:
        if randf() < drop.chance:
            items.append(drop.item)
    
    return items

# loot_drop.gd
class_name LootDrop
extends Resource

@export var item: Item
@export var chance: float = 0.5
@export var min_amount: int = 1
@export var max_amount: int = 1

Best Practices

1. Balance - Test economy carefully
2. Sinks - Provide money sinks (repairs, etc.)
3. Inflation - Control money generation

Reference

• Related: godot-inventory-system, godot-save-load-systems

Related

• Master Skill: godot-master