This module lets you add debugging instructions which look like comments and do nothing unless you 'use' this module. use Devel::StealthDebug; my $foo = 0; # ... Several processing on $foo my $bar = 1 / $foo; #!assert($foo != 0)! my %myhash; #!watch(%myhash)! sub func1 { #!emit(Entering func1)! #... } WWW: https://metacpan.org/release/Devel-StealthDebug