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.
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.
Fresh and moving items are evaluated more frequently for responsive merging, while settled piles use a slower scan cadence to reduce unnecessary server work.
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.
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.
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:
When a logical mob needs to behave independently, Jar Stacker can safely extract it from the stack as its own physical entity.
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:
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:
Jar Stacker includes additional logic for gameplay systems that normally depend on individual mob state.
Examples include:
When an interaction cannot safely remain virtualized inside a stack, the affected mob can be extracted while preserving its logical state.
Jar Stacker provides configurable item and mob stacking behavior.
You can configure:
Configuration can be accessed through:
/jarstacker configYetAnotherConfigLib (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.
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 informationSome administrative commands require operator permissions.
Jar Stacker v0.7.0 supports 15 verified Minecraft runtimes using 9 release artifacts.
| Minecraft Version | Jar Stacker File | Java |
|---|---|---|
| 1.21.1 | jarstacker-0.7.0+mc1.21.1.jar |
Java 21 |
| 1.21.2 – 1.21.3 | jarstacker-0.7.0+mc1.21.2.jar |
Java 21 |
| 1.21.4 | jarstacker-0.7.0+mc1.21.4.jar |
Java 21 |
| 1.21.5 | jarstacker-0.7.0+mc1.21.5.jar |
Java 21 |
| 1.21.6 – 1.21.8 | jarstacker-0.7.0+mc1.21.6.jar |
Java 21 |
| 1.21.9 – 1.21.10 | jarstacker-0.7.0+mc1.21.9.jar |
Java 21 |
| 1.21.11 | jarstacker-0.7.0+mc1.21.11.jar |
Java 21 |
| 26.1 – 26.1.2 | jarstacker-0.7.0+mc26.1.jar |
Java 25 |
| 26.2 | jarstacker-0.7.0+mc26.2.jar |
Java 25 |
Install only ONE Jar Stacker JAR matching your Minecraft version.
Do not install multiple Jar Stacker version-specific JARs at the same time.
.jar file inside your Minecraft mods folder.Jar Stacker supports both single-player and dedicated server environments.
YACL and Mod Menu are optional and are not required for dedicated-server operation.
Jar Stacker includes an extensive automated integration test suite covering:
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.
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
Wiki / Installation / Config / Commands:
https://wiki-jarstacker.jarengjar.com
Reproducible bug reports and compatibility reports are welcome.
Jar Stacker is licensed under the MIT License.
