BandwidthOptimizer

BandwidthOptimizer is a client-and-server network bandwidth optimization mod for heavily modded Minecraft servers. It reduces repeated and compressible PLAY traffic while trying to preserve the original Minecraft packet stream after decoding.

It is designed for modpacks and public servers where login sync, custom payloads, machine networks, storage systems, and repeated chunk visits can generate large amounts of network traffic. It is not an FPS optimizer, and it should not be treated as a replacement for normal server, proxy, or network tuning.

!BandwidthOptimizer preview

Support

• Discord: https://discord.gg/qdMbM9Rq6B
• GitHub: https://github.com/duckgun13476/BandwidthOptimizer

Development Status

BandwidthOptimizer is still under active development. Bugs and mod compatibility issues are still possible, especially in large modpacks, proxy networks, and servers with heavy custom payload traffic.

The mod is designed to optimize network packets, not to modify world data or save files. When a packet, boundary, or mod interaction looks unsafe, BandwidthOptimizer tries to fall back to direct or bypass behavior instead of forcing optimization.

If you encounter an issue, please report it with client logs, server logs, proxy logs if applicable, and BandwidthOptimizer report files. Compatibility reports, suggestions, and contributions are welcome.

What It Does

• Wraps already encoded Minecraft packets into reversible transport frames.
• Compresses suitable packet payloads with streaming Zstd.
• Uses synchronized literal/template mapping for repeated packet structures.
• Batches safe small packet groups while respecting protocol and flush boundaries.
• Reuses chunk data through full, ref, and patch transport decisions.
• Keeps reusable chunk cache data across reconnects and compatible proxy server switches.
• Bypasses sensitive packets, protocol transitions, and unsafe timing boundaries instead of forcing every packet through the same optimization path.
• Provides HUD, server stats, source reports, bypass reports, and decoder dump files for debugging and reproducible measurements.

How It Works

BandwidthOptimizer works below normal gameplay logic. On the sending side, it observes packets after Minecraft or the loader has encoded a complete packet into bytes. The transport layer may then wrap, batch, compress, or bypass that encoded packet.

On the receiving side, the transport frame is unwrapped back into the original encoded packet bytes before normal packet handling continues. The design goal is packet-stream equivalence: after restoration, the receiver should see the same packet types, packet contents, and relative order that it would have seen without BandwidthOptimizer.

Layer	Purpose
Transparent transport	Carries already encoded packet bytes without rewriting gameplay logic.
Streaming Zstd	Compresses packet bodies that benefit from byte-level compression.
Literal/template mapping	Reduces repeated packet structures while keeping sender and receiver state synchronized.
Light batch path	Uses cheaper batch encoding for sensitive flush paths where full template work is too expensive.
Chunk transport	Chooses full, ref, patch, or bypass for chunk-related traffic based on available cache state and safety checks.
Boundary control	Forces flush, bypass, warmup, or reset around protocol transitions, login/config/play changes, proxy switches, and stale epochs.
Reports	Records raw traffic, optimized traffic, bypass causes, packet ranks, and decoder failures for troubleshooting.

Measured Results

Bandwidth reduction depends on the modpack, player activity, proxy setup, and which packets dominate the traffic. The examples below are from BandwidthOptimizer report files collected during real heavily modded server testing. They are examples, not guaranteed results.

The main metric for this mod is the compression ratio of traffic that actually enters BandwidthOptimizer's transport path. Whole-server raw/actual totals are useful context, but they also include direct packets, compatibility bypasses, cache reuse, and traffic from mods that should not or cannot be compressed. For example, some mod traffic such as WATUT/YSM-style presence or model updates may be bypassed or may compress poorly, so it should not be mixed into the main transport-compression claim.

Live HUD snapshots:

Environment	Client optimized flow	Server raw to actual	Server optimized flow	Direct flow	Players	Source
Create Delight Remake server 1	23.21 MB -> 3.93 MB (16.9%)	305.35 GB -> 51.12 GB (16.7%)	40.28 GB (13.2%)	49.46 GB (16.2%)	13	HUD snapshot, v2.7.6.10.
Create Delight Remake server 2	24.51 MB -> 4.15 MB (16.9%)	516.70 GB -> 83.24 GB (16.1%)	57.57 GB (11.1%)	57.01 GB (11.0%)	15	HUD snapshot, v2.7.6.10.

Source-report managed transport totals:

Environment	Managed transport	Without WATUT/YSM-like streams	Notes
Create-focused core server	38976.09 MiB -> 9455.03 MiB (24.3%)	34580.44 MiB -> 5236.56 MiB (15.1%)	Real mixed traffic with large already-compressed/poorly-compressible sources.
Create-focused mirror server	1046.16 MiB -> 253.89 MiB (24.3%)	902.82 MiB -> 113.55 MiB (12.6%)	Smaller mixed sample; WATUT-like traffic is visible.
Create-focused test server	1174.31 MiB -> 112.24 MiB (9.6%)	same sample	No WATUT/YSM exception in this TopN sample.
Create Delight	7865.72 MiB -> 1622.43 MiB (20.6%)	7774.54 MiB -> 1539.90 MiB (19.8%)	Public modpack source-report snapshot.
Create Delight secondary snapshot	4567.66 MiB -> 603.15 MiB (13.2%)	not separated	Earlier report snapshot.

High-impact traffic-source examples:

Source	Environment	Raw observed	Actual transmitted	Actual/raw ratio
ClientboundLevelChunkWithLightPacket	Create-focused core server	9062.88 MiB	481.85 MiB	5.3%
ClientboundLevelChunkWithLightPacket	Create-focused test server	713.65 MiB	16.84 MiB	2.4%
ClientboundTabListPacket	Create-focused core server	6354.97 MiB	655.45 MiB	10.3%
lightmanscurrency:network	Create-focused core server	8206.80 MiB	593.69 MiB	7.2%
create:deployer block entity data	Create Delight	510.41 MiB	71.61 MiB	14.0%

Low-benefit traffic-source examples:

Source	Environment	Raw observed	Actual transmitted	Actual/raw ratio	Path
watut:main	Create-focused core server	4157.94 MiB	3974.80 MiB	95.6%	BATCH_DIRECT_FALLBACK
yes_steve_model:2_6_0	Create-focused core server	514.63 MiB	510.50 MiB	99.2%	BATCH_TRANSPORT_SHARE
watut:main	Create-focused mirror server	146.07 MiB	143.07 MiB	97.9%	BATCH_TRANSPORT_SHARE
watut:main	Create Delight	91.18 MiB	82.53 MiB	90.5%	BATCH_TRANSPORT_SHARE

These streams are already compressed, encrypted, or near-random enough that a second compression layer has little room to help. They are still shown here because they explain why mixed-server totals can look worse than the high-impact packet families above.

To reproduce comparable measurements on your own server:

1. Install the same BandwidthOptimizer version on the server and clients.
2. Run the same activity pattern for a fixed period, such as login bursts, repeated chunk travel, machine-heavy areas, or normal online play.
3. Prefer the HUD optimized flow line, or filter source reports to rows whose path enters transport, such as BATCH_TRANSPORT_*, SINGLE_TRANSPORT, or chunk transport rows.
4. Keep direct/bypass rows separate. Do not count bandwidthoptimizer:transport carrier packets as new raw source traffic.
5. Include the modpack, loader, Minecraft version, player count, and test duration when sharing results.

Important report locations:

bandwidthoptimizer-native/transport-source-report/latest-source-report.md
bandwidthoptimizer-native/transport-bypass-report/latest-bypass-report.md
bandwidthoptimizer-native/decoder-exception-dump/

Mechanomania was also checked with BandwidthOptimizer diagnostic output in the current test set. The available snapshot contained bypass and packet-rank reports but not a source raw/actual summary, so it is listed as a tested environment rather than used as a compression-ratio claim.

Tested Modpack Environments

The author has tested BandwidthOptimizer in several heavily modded environments, including:

• Create Delight
• Brass Concerto
• Aeronautics
• Mechanomania

This means these environments have been used for compatibility testing. It does not guarantee that every possible mod combination, proxy topology, or server configuration is covered.

Supported Versions

Choose the build that matches both your Minecraft version and loader.

Loader	Minecraft	Notes
Forge	1.19.2	Forge 43.x target.
Forge	1.20.1	Forge 47.x target.
Fabric / Quilt	1.20.1	Requires Fabric API. Published for Fabric and Quilt loaders.
Fabric / Quilt	1.21.1	Requires Fabric API. Published for Fabric and Quilt loaders.
NeoForge	1.21.1	NeoForge 21.x target.

Dependencies

• Minecraft and the matching mod loader for the downloaded build.
• Fabric API for Fabric and Quilt builds.
• The same BandwidthOptimizer version on both the server and every client.

Forge and NeoForge builds use loader config files generated under config/. Fabric and Quilt builds include matching runtime code and still require Fabric API.

Installation

1. Download the BandwidthOptimizer jar for your loader and Minecraft version.
2. Put the jar into the server mods folder.
3. Put the same BandwidthOptimizer version into each client mods folder.
4. Install Fabric API when using the Fabric or Quilt build.
5. Restart the server and clients.

If client and server versions do not match, the transport channel may be disabled or fail to negotiate correctly.

Configuration

Main loader-generated config files:

config/bandwidthoptimizer-common.toml
config/bandwidthoptimizer-client.toml

Important areas:

Area	Purpose
PLAY batch options	Controls reference deduplication, SHA-256 dictionary, template dictionary, Zstd, streaming Zstd, and async batch encoding.
Template dictionary limits	Caps packet size, entry count, payload bytes, diff runs, and changed bytes for mapping work.
Chunk cache budget	Controls client-side chunk cache memory and persistent backup behavior.
Debug analysis	Enables heavier manual analysis commands such as transport reports and packet ranks.
Decoder dump	Writes detailed packet dumps when decoder failures are detected.
Runtime properties	Advanced overrides such as bandwidthoptimizer.transport.batchWindowMillis, bandwidthoptimizer.transport.mappingEnabled, and bandwidthoptimizer.transport.zstdEnabled.

Most servers should start with the default configuration and only change these options while comparing report output before and after the change.

Commands

Command	Description
/bandwidthoptimizer	Shows available BandwidthOptimizer commands.
/bandwidthoptimizer hud	Toggles the client HUD.
/bandwidthoptimizer stats	Shows server bandwidth totals.
/bandwidthoptimizer stats total	Shows persisted total server bandwidth stats.
/bandwidthoptimizer stats players [limit]	Shows top player/channel bandwidth stats.
/bandwidthoptimizer stats reset	Resets persisted server bandwidth stats.
/bandwidthoptimizer test transportreport run [ticks]	Starts a short transport compression report. Requires debug analysis.
/bandwidthoptimizer test transportreport status	Shows transport report capture status.
/bandwidthoptimizer test packetrank run [ticks]	Starts a packet-rank capture. Requires debug analysis.
/bandwidthoptimizer test packetrank status	Shows packet-rank capture status.

Compatibility Scope

BandwidthOptimizer intentionally bypasses or flushes around packets and states where optimization could change observable timing or ordering. This includes protocol transitions, strong timing boundaries, stale transport epochs, unsafe serverbound carrier sizes, selected compatibility cases, and packets where direct delivery is safer than wrapping.

Velocity proxy setups are supported and tested, but proxy switching and reconnect behavior can expose timing-sensitive bugs in any transport layer. When reporting a proxy issue, include client logs, backend server logs, proxy logs, and the generated BandwidthOptimizer report files.

Limitations

• Both the client and server must install the mod.
• Results vary by modpack, online count, traffic source, and activity pattern.
• Already-compressed, encrypted, or near-random streams such as WATUT/YSM-style presence or model data may have little or no additional compression benefit.
• Some packets are deliberately sent directly because optimizing them would cost more than it saves or could risk compatibility.
• Large login or reconnect bursts can still create network pressure even when compressed.
• BandwidthOptimizer reduces network traffic; it does not directly optimize FPS, TPS, world generation, database latency, or proxy routing.

Reporting Issues

When reporting a problem, please include:

• Minecraft version, loader, and BandwidthOptimizer version.
• Whether a proxy such as Velocity is used.
• Client logs and server logs around the issue time.
• Proxy logs when the problem involves server switching or reconnects.
• latest-source-report.md and latest-bypass-report.md if available.
• Decoder dump files if a packet decoder error was reported.
• The modpack name or a short list of major networking-heavy mods.

Acknowledgments

Thanks to the server owners, modpack maintainers, and players who provided logs, packet dumps, compatibility reports, and real traffic samples from heavily modded servers. Those reports are what make the optimization and compatibility rules practical instead of theoretical.

License

This project is licensed under GNU LGPL 2.1-only.