The current custom close reason for application development question reads:
Questions about web application development are off-topic here, but can be asked on Stack Overflow.
We're doing our compatriots at Stack Overflow a disservice. Most of these questions are crap.
I suggest rephrasing it:
Questions about web application development are off-topic here; they might be on-topic for Stack Overflow.
Perhaps a link to the Stack Overflow Help Center would be good, too.
Or, from Sathya's suggestion...
It is a question about creating/developing a web application.