The JDiagnose Core project contains the JDiagnose framework and a library of a few basic Diagnostics. The Core project has no dependencies and will work on Java 1.3 and above. This to allow for easy embedding in projects. Diagnostics in the Core project include:

Basic JDBC DiagnosticTests a database through a JDBC connection
Check ClassPath DiagnosticMakes sure that all items listed on the ClassPath exist
HTTP(S) URL DiagnosticTests a HTTP(S) URL
Java Version DiagnosticEnsure that you're running with the correct Java Version
JDK DiagnosticTries to make sure that you're running with the JDK
Pingable DiagnosticPings objects that implement the Pingable interface
Tcp DiagnosticTests a Socket
Succeeding DiagnosticTest diagnostic that always succeeds
Failing DiagnosticTest Diagnostic that always fails