Which key packages used compat 4?

# Data file compat-4-packages (one *source* package per line)
$ curl --silent --data-binary @compat-4-packages \
  https://udd.debian.org/cgi-bin/select-key-packages.cgi
alsamixergui
apg
[...]
sgml-base
wwwconfig-common

Also useful for things like bug#830997, which was my excuse for requesting this. :)

Is package foo a key package (yet)?

$ is-key-pkg() {
 RES=$(echo "$1" | curl --silent --data-binary @- \
    https://udd.debian.org/cgi-bin/select-key-packages.cgi)
 if [ "$RES" ]; then
   echo yes
 else
   echo no
 fi
}
$ is-key-pkg bash
yes
$ is-key-pkg mscgen
no
$ is-key-pkg NotAPackage
no

Above shell snippets might need tweaking for better error handling, etc.

Once again, thanks to Lucas for the server-side UDD script. :)