Difference between JAVA_OPTS and JAVA_TOOL_OPTIONS?

JAVA_TOOL_OPTIONS is read by some JDK tools, but has limited applicability.

JAVA_OPTS is a convention used by Apache Tomcat and some other apps, but is not read directly by any JDK tools published by Sun/Oracle, AFAIK.

From: https://forums.oracle.com/forums/thread.jspa?messageID=6438415

JAVA_OPTS is not an environment variable that the java executable will recognize on it's own. Instead, various scripts which wrap the start up of java will often use an environment variable named JAVA_OPTS to configure the java executable (for example, the tomcat startup script does this).

see "what is" doc and "tool options" doc

Basically, the JAVA_TOOL_OPTIONS is intended for use by development tools, monitoring tools and the like whereas JAVA_OPTS is used for running 'general' Java programs, I think people tend to mix and match somewhat (from what Google has shown me example wise).