IDT date format on connection level (oracle)

When running below query on SQL Developer it works fine:

select * from [table_name] where DATE = '15-OCT-18'

But when running sql on connection level in IDT or free hand SQL in BO I get no results.

Only below reformatting worked:

to_date('10/15/18', 'MM/DD/YY')

I would like to understand how to check how IDT is formatting date to MM/DD/YY format because when I ran freehand SQL on BO level (with different filter) I got date with that format.