It's included in the message for the constructor, but not accessors...
$ perl -Ilib -E'package Foo; use Moo; use Types::Standard -types; has foo => (is=>"rw",isa=>Int); Foo->new(foo => 1.1)'
Value "1.1" did not pass type constraint "Int" (in $self->{"foo"}) at (eval 223) line 40
Value "1.1" did not pass type constraint "Int" (in $self->{"foo"})
"Int" is defined as: (defined $_ and $_ =~ /\A-?[0-9]+\z/)
$ perl -Ilib -E'package Foo; use Moo; use Types::Standard -types; has foo => (is=>"rw",isa=>Int); Foo->new->foo(1.1)'
Value "1.1" did not pass type constraint "Int" at (eval 224) line 15
Value "1.1" did not pass type constraint "Int"
"Int" is defined as: (defined $_ and $_ =~ /\A-?[0-9]+\z/)