> It's part of Java/Jakarta EE.

If it's part of J2EE, it's in practice "part of Java" since the JDK comes with the J2EE packages built-in...

That is, it came with the J2EE packages built-in, until Java 11 decided to break everything, and force people to get each piece of J2EE from a separate upstream project, with AFAIK no "all of J2EE" uber-jar you could simply copy into your project to restore the status quo. It's no wonder so many projects are to this day stuck on Java 8.

> since the JDK comes with the J2EE packages built-in...

Are you sure about that? I just downloaded the Java 8 JDK, and javax.json is not there. And the documentation doesn't mention it either. What am I missing?

The JDK doesn't include all the J2EE goodness: https://docs.oracle.com/javaee/7/api/javax/json/package-summ...