Jar Stacker

Jar Stacker is a performance-focused entity stacking mod for Minecraft Java Edition 1.21.1 through 26.2 (Fabric).

It reduces the number of physical dropped items and mobs in the world by consolidating compatible entities while preserving important Vanilla gameplay behavior and individual logical state.

Fewer physical entities. Less unnecessary entity processing. Vanilla-aware gameplay behavior.

📦 Item Stacking

Nearby compatible dropped items are automatically consolidated into a single pile.

Jar Stacker uses a Latest Entity Wins architecture: when compatible item piles merge, the newest dropped item remains as the physical entity and absorbs the count of nearby compatible piles.

Highlights

• Broad-radius item consolidation
• Adaptive scanning for newly dropped, moving, and settled items
• Exact item-count preservation
• Overflow protection
• Preserves item components, durability, enchantments, and custom data
• Natural Vanilla item position and velocity
• No artificial merge animation
• No survivor teleportation
• Configurable stack labels

Fresh and moving items are evaluated more frequently for responsive merging, while settled piles use a slower scan cadence to reduce unnecessary server work.

🐄 Mob Stacking

Compatible mobs can be represented by a single physical entity while Jar Stacker keeps track of the individual logical members inside the stack.

Unlike simple stacking systems that only store a number, Jar Stacker preserves gameplay-critical state for logical mob members.

Logical state includes

• Individual health
• Status effects
• Fire timers
• Growth state
• Breeding state
• Variant-sensitive state
• Equipment-sensitive behavior
• Mob interactions
• Combat and death state

Jar Stacker maintains strict logical-state consistency so that a stacked mob represents the same number of logical members as the state records stored for that stack.

This allows large groups of mobs to use fewer physical entities while keeping their gameplay behavior much closer to Vanilla Minecraft.

⚔️ Vanilla-Aware Combat

Stacked mobs are not treated as one giant health bar.

Jar Stacker tracks logical health and uses Vanilla combat behavior to determine what happened before expanding that result to the appropriate logical members of the stack.

Supported behavior includes:

• Single-target attacks
• Sweeping attacks
• Area damage
• Environmental damage
• Projectile damage
• Multiple logical deaths from one attack
• Loot and XP generation
• Player kill attribution
• Looting-aware death behavior
• Equipment-sensitive extraction

When a logical mob needs to behave independently, Jar Stacker can safely extract it from the stack as its own physical entity.

🧪 Status Effects & Fire

Status effects are tracked independently for logical members of a mob stack.

Jar Stacker includes handling for the full Vanilla status-effect registry across supported Minecraft versions, including effects with special hurt or death behavior such as:

• Infested
• Oozing
• Weaving
• Wind Charged

Minecraft 1.21.x contains 39 Vanilla status effects, while Minecraft 26.x contains 40 Vanilla status effects in the versions currently supported by Jar Stacker.

Fire duration is also tracked independently for logical mob members rather than being flattened into one shared timer.

Jar Stacker additionally handles:

• Persistent logical fire timers
• Sunlight burning for undead mobs
• Environmental ignition
• Targeted melee ignition
• Flaming projectiles
• Water, rain, and powder-snow extinguishing behavior

🐑 Animals, Growth & Interactions

Jar Stacker includes additional logic for gameplay systems that normally depend on individual mob state.

Examples include:

• Baby mob growth
• Feeding
• Breeding
• Breeding cooldowns
• Sheep wool regrowth
• Mooshroom interactions
• Saddling
• Mob transformations
• Equipment pickup
• Variant-aware compatibility checks

When an interaction cannot safely remain virtualized inside a stack, the affected mob can be extracted while preserving its logical state.

⚙️ Configuration

Jar Stacker provides configurable item and mob stacking behavior.

You can configure:

• Item stacking radius
• Mob stacking radius
• Maximum stack sizes
• Item and mob whitelists / blacklists
• Per-item rules
• Per-mob rules
• Stack labels
• Debug settings

In-Game Configuration

Configuration can be accessed through:

• /jarstacker config
• Mod Menu

YetAnotherConfigLib (YACL) and Mod Menu are optional but recommended for the best configuration experience.

Jar Stacker also provides a built-in fallback configuration interface when YACL is not installed.

Server configuration is authoritative in multiplayer.

📋 Commands

Useful Jar Stacker commands include:

• /jarstacker config — Open configuration
• /jarstacker inspect — Inspect a targeted stack
• /jarstacker status — View stacking information
• /jarstacker reload — Reload configuration
• /jarstacker items <on|off> — Toggle item stacking
• /jarstacker mobs <on|off> — Toggle mob stacking
• /jarstacker debug — Toggle debugging information

Some administrative commands require operator permissions.

🎮 Supported Minecraft Versions

Jar Stacker v0.7.0 supports 15 verified Minecraft runtimes using 9 release artifacts.

Install only ONE Jar Stacker JAR matching your Minecraft version.

Do not install multiple Jar Stacker version-specific JARs at the same time.

📦 Requirements

Required

• Minecraft Java Edition: 1.21.1 – 26.2
• Fabric Loader: 0.19.3+
• Fabric API
• Java 21: Minecraft 1.21.x
• Java 25: Minecraft 26.x

Optional

• YetAnotherConfigLib (YACL v3) — Enhanced configuration interface
• Mod Menu — Easy access to the configuration screen

🔧 Installation

1. Install Fabric Loader for your Minecraft version.
2. Install the matching version of Fabric API.
3. Make sure you are using:
   • Java 21 for Minecraft 1.21.x
   • Java 25 for Minecraft 26.x
4. Download the single Jar Stacker file matching your Minecraft version.
5. Place the .jar file inside your Minecraft mods folder.
6. Optionally install YACL and Mod Menu.

Jar Stacker supports both single-player and dedicated server environments.

YACL and Mod Menu are optional and are not required for dedicated-server operation.

✅ Verification

Jar Stacker includes an extensive automated integration test suite covering:

• Item stacking and count conservation
• Real block-drop behavior
• Mob logical state
• Health and damage
• Combat attribution
• Sweeping and projectile combat
• Status effects
• Persistent fire
• Sunlight and environmental ignition
• Breeding and growth
• Variant compatibility
• Mob transformations
• Save/load persistence
• Cross-version state preservation

Current v0.7.0 Results

• 360 / 360 automated server tests passing per runtime
• 15 supported runtimes verified
• 5,400 / 5,400 total server tests passing
• 15 / 15 client boot/linkage checks passing
• Minecraft 26.2 gameplay manually verified
• Minecraft 26.1.2 → 26.2 save upgrade verified

💾 Save Compatibility

Jar Stacker preserves its established logical stack and configuration formats across the supported release architecture.

Cross-version world upgrade from Minecraft 26.1.2 to 26.2 has been explicitly verified with Jar Stacker state preserved.

As with any Minecraft or mod upgrade:

Always back up your world before updating.

Minecraft world downgrades are not supported.

🐛 Source Code & Bug Reports

Jar Stacker is open source.

Source:
https://github.com/rametrree/Jar-Stacker

Releases:
https://github.com/rametrree/Jar-Stacker/releases

Issues:
https://github.com/rametrree/Jar-Stacker/issues

Reproducible bug reports and compatibility reports are welcome.

📜 License

Jar Stacker is licensed under the MIT License.