Dear Maintainer,
It seems like grep-available, grep-aptavail (and possibly the other tools) search only the first line of the Description field.
The manual claims the search is as per 'apt-cache', which would be more powerful and it sounds to me as the desired behavior.

Quoting manpage grep-dctrl(1):
    % grep-available -F Package -F Description foo
    This kind of search is the exactly same that apt-cache does.
Actual behaviour:
    $ grep-available -F Package -F Description foo | wc     # manpage-verbatim, except for 'wc'
        0   0   0
but apt-cache finds results even for "foo"
    $  apt-cache search foo | wc
        440    3702   27827
    $ apt-cache search --names-only foo | wc  # just a double-check I tried
        25     210    1657

As another example, the string 'grep-aptavail' occurs deep in the Description of dctrl-tools, so we get:
    $ apt-cache search grep-available
       dctrl-tools - Command-line tools to process Debian package information
    $ grep-aptavail -F Package -F Description grep-aptavail
       -> (it finds nothing)
    $ grep-available -F Package -F Description grep-available
       -> (it finds nothing)

It seems to me that searching only the 1st line reduces the power of the tool(s), but if the above behavior is correct, I would suggest updating the manpage.

Thank you for your attention.
R.P.