it also allows you to run arbitrary perl code

you're supposed to be able to view vars at each stackframe , but that doesn't work -- and that is only other functionality that is anything like perl5db.pl

Not surprising, those things are hard to reinvent, require a lot of work ... Miyagawa can't do everything, someone has to pick up the slack, speaking of which, another abandoned proof of concept is Plack::Middleware::Scrutiny ... had more potential (its based on Devel::ebug)

Then see Plack::Debugger / LPW2014 Stevan Little ‎stevan‎ ‎Plack::Debugger A new debugger for Plack Applications‎ - YouTube

Debuggers are a lot of work, a lot of them get started ...

I always found using debuggers more work than actual work