Diagnose Java server lag

Lag type	Common signs
Server-side	The world slows for everyone, mobs freeze, or mined blocks reappear.
Connection	One or more players have delayed actions or rubber-band while moving.
Client	One player’s display stutters or loses frames while the server continues normally.

Lag type

Common signs

Server-side

The world slows for everyone, mobs freeze, or mined blocks reappear.

Connection

One or more players have delayed actions or rubber-band while moving.

Client

One player’s display stutters or loses frames while the server continues normally.

Check server-side causes

Read the console for repeated errors, watchdog warnings, or overloaded messages.

Check whether the problem began after adding a plugin, mod, add-on, farm, redstone machine, or large group of entities.

Review view-distance, simulation-distance, and entity-broadcast-range-percentage in server.properties.

Test one change at a time and compare performance under similar player load.

Profile the server with spark

Use spark on compatible plugin server software to find expensive plugins, tasks, entities, and server threads.

Install spark

Install a compatible spark .jar by following Install Java plugins, then restart the server.

Start a profiler

Run the profiler during the lag you want to investigate.

spark profiler start

Stop and open the report

Let it collect representative activity, then stop it.

spark profiler stop

Open the generated report link.

Read the result

Check TPS, milliseconds per tick, memory and garbage collection, then inspect the plugin, mod, world, or thread consuming the most processing time.

A spark report may contain server details. Review it before sharing the link publicly.

Server properties

Adjust view, simulation, and entity broadcast distances.

Generate chunks before high-speed exploration.