spark: How to Find What's Causing Lag on Your Minecraft Server

What spark is and where to find it

spark is a profiler: it looks many times per second at what the server is doing and adds it up. At the end you get a tree with the percentage of time each thing takes, like the Windows Task Manager, but inside Minecraft.

On Paper it's included since 1.21: it's the official profiler and replaces the old “timings”, which Paper switched off. There's nothing to install; the commands start with /spark and require admin (op).

On Fabric, Forge or NeoForge it's a mod you install only on the server (players don't need it). It's on Modrinth under the name spark.

First, the pulse: /spark tps

It shows TPS (ticks per second) for the last minute, the last 5 and the last 15, and MSPT: the milliseconds each tick takes. Minecraft wants 20 ticks per second, so each tick has 50 ms. With MSPT below 50, the server has headroom even though TPS says 20; above 50, TPS starts to drop and you notice it.

If TPS is at 20 and someone still stutters, the problem isn't the server but that player's connection or computer (the lag guide explains it).

/spark health gives a fuller snapshot: TPS, MSPT, memory used, CPU and disk usage. It's the first thing worth pasting if you ask someone for help.

Find the culprit: the profiler

1. Wait until there's lag

   Profiling an empty server is pointless. Do it when the lag is noticeable: with people online, while exploring or when the farms are loaded.

2. Start it with a fixed duration

   /spark profiler start --timeout 300 leaves it measuring for 5 minutes and it stops on its own. With less than a couple of minutes the report comes out too noisy.

3. Open the link

   When it finishes, spark uploads the report and gives you a link to its web viewer. There's nothing to download; you can pass the link to whoever is helping you.

4. If the lag comes in spikes

   For one-second freezes that come and go, it's better to use /spark profiler start --only-ticks-over 100 --timeout 300: that way it only records ticks that took longer than 100 ms, and the culprit doesn't get diluted among the good ticks.

How to read the report without being a programmer

At the top there's a tree starting at “Server thread”, the main thread where the whole game happens. Keep expanding the branch with the highest percentage, without stopping at the small ones.

If, as you go down, the name of a plugin or mod appears (spark marks it on the right of each line) with a large percentage, you have a suspect. Plugins normally take very little; one that takes 20 or 30 % of the tick has a problem or a configuration that asks too much.

If what weighs most has “entity” or “chunk” in its name, it's the world: too many animals, items on the ground, villagers or hoppers. If chunk generation is heavy, you're exploring new areas.

And if nothing stands out but the report shows a lot of time in “GC” (Java's garbage collector), memory is tight: the server spends its time cleaning it up.

What to do with what you find

A plugin or a mod: check whether there's a newer version, review its configuration (many have tasks every few ticks that can be spaced out) or replace it with another that does the same job. Make a backup before removing anything.

Entities: limit the size of farms, clear up loose items and don't cram villagers together. Lowering “simulation-distance” in server.properties reduces what's simulated around each player and usually makes a big difference.

World generation: pregenerate the world with Chunky and set a border with /worldborder. Once an area has been explored, it no longer costs anything.

Memory: if GC pauses are long and frequent, the server needs more RAM or fewer mods. That's the case where more RAM does fix the lag.

On NapNodes

Minecraft servers come on Paper with the latest version, so spark is already there: open the server's “Console” in the panel and type spark tps (in the console, without the slash). On “Home”, the server screen, you see how much memory and CPU it's using at the same time, and under “Advanced settings” → “Performance”, its graphs.

Your plan's RAM is yours alone, with no overselling: if spark says the lag is your world or your plugins, you fix it on your server; it doesn't depend on what other customers do on the same machine. And if it turns out you're short of memory, you give it more without reinstalling anything or losing the world: “More RAM” in “My plan & invoices” or “Buy RAM” in “My servers” (the guide to giving it more RAM explains it).

On Fabric, Forge or NeoForge, search for it in the panel's “Mods & plugins” and it installs in one click.

Frequently asked questions