Lightning Profiler

Found a bug or have an idea? Please post it on GitHub Issues instead of the comments. That's where every report gets read and tracked.

Lightning finds out what's making your game slow and tells you in plain English. A profiler for frames, ticks, graphics, memory and mods, for Minecraft 1.21.1 with NeoForge.

Type /lightning report, play for a minute, and a report opens in your browser. Its first page lists the biggest problems with the evidence underneath.

What it records

• Frames and server ticks on one timeline, with stalls, garbage-collection pauses and log lines marked where they happened.
• Graphics card time per render step, including shader packs (Iris) and distant terrain.
• Which mod is behind slow code, memory use and memory churn.
• Chunks, mobs and machines that cost the most server time, with a chunk map.
• Phases: mark moments like "boss fight" and compare them side by side.

Slow start-up or world joins

Every loading step is timed from the moment Java starts: the slowest resource loaders, which mods' mixins slow loading, and what the game sat waiting on. Add this to the game's Java arguments, launch, and open the report's Loading tab:

-Dlightning.startup=join -XX:StartFlightRecording=name=lightning,settings=profile,class-loading=true

Use title instead of join to stop at the title screen.

Commands

Lightning reports its own overhead, and if the game crashes mid-recording the report is rebuilt the next time you start. Each recorder can be turned on or off in Mods → Lightning → Config.

Credits

Source code on GitHub, licensed LGPL-3.0-only.

Made with AI assistance.