What are the best JVM flags for a Minecraft server?

Aikar's flags (a tuned G1GC configuration) are the community standard. Set -Xms and -Xmx to the same value matching your plan's RAM, then add the G1GC flags.

Should Xms and Xmx be the same?

Yes — setting -Xms equal to -Xmx avoids the JVM resizing the heap, which reduces lag spikes. Match both to your server plan RAM (leaving a little headroom on small plans).

Optimization Guide

Best Minecraft
Server JVM Flags

The community-standard "Aikar flags" tune Java's garbage collector to smooth out lag spikes. Copy, set your RAM, done.

-Xms6G -Xmx6G -XX:+UseG1GC -XX:+ParallelRefProcEnabled -XX:MaxGCPauseMillis=200 -XX:+UnlockExperimentalVMOptions -XX:+DisableExplicitGC -XX:+AlwaysPreTouch -XX:G1NewSizePercent=30 -XX:G1MaxNewSizePercent=40 -XX:G1HeapRegionSize=8M -XX:G1ReservePercent=20 -XX:+UseStringDeduplication

Replace 6G with your plan's RAM (keep -Xms and -Xmx equal). Not sure how much? Calculate it →

Set -Xms and -Xmx equal

These set the minimum and maximum heap. Making them equal stops the JVM from resizing memory mid-game, which is a common cause of lag spikes. Match them to your plan's RAM.

Why G1GC + these flags

G1GC is the garbage collector best suited to Minecraft's memory pattern. The extra flags shorten and smooth GC pauses so you get steadier TPS instead of periodic freezes — especially on modded servers.

Most hosts set these for you

On a managed host, these flags are often applied automatically or via a one-click "optimized flags" toggle. If you self-host, paste them into your start script. See our reduce-lag guide for the rest.

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