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Performance tuning

Laggy game, slow startup, slow downloads? Adjust these spots as needed; they resolve most performance problems.

Pick the right Java

The launcher offers Java 8 / 11 / 17 / 21 / 25 / 26 and several other versions, choosing automatically per game version: 1.16 uses Java 11, 1.17 uses Java 16, 1.18–1.20.4 use Java 17, 1.20.5+ use Java 21, and 26.1+ uses Java 25 (older versions use Java 8).
  • Prefer letting the launcher download it: Settings → Java runtime → Download. JDKs downloaded automatically have the best game compatibility
  • Java already on your machine can be adopted by scanning, but JREs of unknown origin (for example, ones bundled by some adware) may be broken; remove them when they are flagged as abnormal

Memory allocation

Settings → Java runtime → Default configuration: Automatic allocation gives the game 70% of available memory (512MiB minimum); manual allocation ranges from 512MiB up to available memory in steps of 256MiB. An oversized Java heap makes garbage collection pauses longer and produces regular stutters in game. Give it just enough.

Launch arguments

Settings → Java runtime → Default configuration → JVM arguments. If the modpack author provides recommended arguments, follow the modpack; otherwise keep the defaults (the launcher already includes sensible garbage collection arguments). Tuning by hand is advanced territory — write down the original values before you change anything.

Downloads and network

  • Slow downloads: turn on Automatically select the fastest download source / Automatically select download source. For the mirror path mapping, see Download mirrors
  • Web pages or the resource center will not load: configure a proxy (Settings → Network settings); it affects only the launcher, not the game
  • Certificate errors behind a proxy: temporarily enable Ignore SSL certificate verification while troubleshooting, then turn it off once the issue is confirmed

Interface smoothness

On low-end machines, do these three things first (Settings → Appearance):
  • Set Component material back to default (liquid glass, acrylic, and frosted glass all cost compositing work)
  • Lower or disable Page animations
  • Limit the frame rate cap to 60 (saves power and reduces overheating)

Data and cache

  • Version list cache (Settings → Storage and cache): extend the cache duration when CurseForge/NeoForge lists load slowly
  • Clear the download task list, export or clear logs: the Toolbox and logs section in Settings