In order to enhance POJO-generation facility I have made some (yet rather minor) changes in org.hibernate.tool.hbm2x.POJOExporter

I rebuild the jar using standard ant task from hibernateExt and deployed it to eclipse\plugins\org.hibernate.eclipse_3.1.0.alpha5\lib\tools
(I unpacked the jar before)

After restarting eclipse hibernate-tools is not starting anymore. I don't know why since the methods changed by me have not even called so far.
There is no message in .log
I verfied contents of the jar - it seems ok.

Q: is there some signature that controls the version of the jar?

(I'm new to eclipse-plugin-development)

I have problems when add new plugins with old one in eclipse 3.1
try with -clean options or delete ECLIPSE_INSTALL/configuration/org.eclipse.*

you have to add hibernate-tools in lib/tools (not unpack it)

If it doesn't work try build org.hibernate.eclipse plugin again - in eclipse drop hibernate-tools.jar
in lib/tools and export new packages in MAINIFEST.MF, if you have new packages - then export hibernate feature

regards