Start a recording
/jfr startBegins recording; the game confirms with JFR profiling started.
/jfr command in Minecraft
/jfr starts and stops a Java Flight Recorder session on the server. The recording captures detailed performance data, which developers and server admins later open in a JFR analysis tool to find the real source of lag.
Syntax
/jfr start/jfr stop// In single player with cheats on, you have level 4, so it works there too.
Examples
Stop and save
/jfr stopEnds the recording and prints the path of the saved file.
Build your commandFill in the fields, then copy the command.
Command generatorHow a recording works
jfr start answers JFR profiling started. Reproduce the lag, then run jfr stop: the game saves the recording and shows the path of the file in chat. The file uses the standard JFR format, readable with tools such as JDK Mission Control.
Who uses it
/jfr needs permission level 4, the highest. Run it while the lag happens, not afterwards, so the recording captures the problem. For a quicker check without external tools, /perf makes a 10 second report and /debug measures ticks per second.
✓ Checked in Java Edition 26.3 · updated 2 November 2026
/jfr: FAQ
Where is the JFR file saved?
The path appears in chat after /jfr stop, at the end of the message JFR profiling stopped and dumped to.
How do I open a .jfr file?
Use a tool that reads Java Flight Recorder files, such as JDK Mission Control. The file is not meant to be read in the game.
How do I use /jfr?
In single player with cheats on, or on a server as an operator or from the server console: /jfr start.
Who can use /jfr?
Server owner or console, level 4. In single player with cheats on, you have level 4, so it works there too.
Since when does /jfr exist?
It is in the official command tree since Java Edition 1.18.