Forge Server Tools · every failure mode · guides
Server failed to initialise — look for the Caused by — FATAL
A generic wrapper thrown when startup aborted. The vanilla frames in this trace are just the call path; they never name the cause.
Search this report for 'Caused by:' and read the LAST one -- that is the real throwable. If there is no Caused by, the cause was logged earlier: open latest.log and read the ERROR lines immediately BEFORE the crash timestamp. A failed datapack, a bad config or a mod that threw during server-start events are the usual three.
Search your crash report or latest.log for any of these:
java.lang.IllegalStateException: Failed to initialize server
The free edition covers the six most common startup failures, and this is not one of them — it is in the paid tool, which checks all 24 and names the mod jar from the stack trace. The fix above is the same one it prints, so you do not need it to solve this.