/jfr

Starts or stops a Java Flight Recorder (JFR) profiling session. JFR is a diagnostic tool built into the JVM that captures detailed performance data.

Syntax

/jfr (start|stop)

Name	Required	Description
start\|stop	Yes	Whether to begin or end the profiling session.

/jfr start
/jfr stop

Requires permission level 4 (server owner).
Added in Java Edition 1.18 (snapshot 21w40a).
The resulting JFR recording is saved as a .jfr file that can be analyzed with tools like JDK Mission Control.
Minecraft adds custom JFR events for world generation, chunk loading, tick durations, and network traffic.
Primarily intended for advanced debugging and performance analysis.

This command is not typically used from command blocks. It requires the highest permission level and is a diagnostic tool for server operators.