Writing DuckDuckGo instant answers is easy

Editor note: some of the information in this article is out of date, see our new DuckDuckGo article for details.

A few weeks ago, I attended NYC Quack & Hack, and learned how to write DuckDuckGo instant answers. Instant answers are really cool: they are micro apps that trigger when a user searches for specific terms. For example if you search for help tmux, you’ll see a tmux cheatsheet displayed. This is a awesome - you can commit code that will go live on DuckDuckGo.com and the good news is that you don’t have to wait until the next Quack & Hack to learn how to write one yourself; DuckDuckGo provide great tools that make it easy.

Setting up the development environment

DuckDuckGo support several different types of instant answers, but today I’m going to focus on creating a cheatsheet, which is displayed by the search engine whenever a user searches for a matching set of keywords.

To get going you’ll need Perl 5.18 or higher and have installed App::DuckPAN, which you can do with cpan or cpanminus:

$ cpan App::DuckPAN
# or
$ cpanm App::DuckPAN

You’ll also need a local copy of DuckDuckGo’s goodies instant answers repo repo, which you can clone with Git:

$ git clone https://github.com/duckduckgo/zeroclickinfo-goodies.git

With both App::DuckPAN and the goodies repo installed, change into the zeroclickinfo-goodies repo, and launch the duckpan server:

$ cd zeroclickinfo-goodies
$ duckpan server

When you run duckpan server, there will probably be a lot of output, but you should see this:

Checking asset cache...
Starting up webserver...
You can stop the webserver with Ctrl-C
HTTP::Server::PSGI: Accepting connections at http://0:5000/

If you open your browser and navigate to http://localhost:5000, you’ll be greeted with the DuckDuckGo search page (try http://0:5000 if localhost doesn’t work). Search for “help tmux” and you should see the same instant answer cheatsheet appear as on the live website.

Creating the instant answer

So now you’ve got the development environment setup, you’re ready to create an instant answer. I’m going to create an instant answer for perldoc (taken from my perldoc article). I can get a headstart on this by creating the skeleton instant answer code with duckpan new:

$ duckpan new PerldocCheatSheet

This creates the basic files required for the instant answer:

Created file: lib/DDG/Goodie/PerldocCheatSheet.pm
Created file: t/PerldocCheatSheet.t
Successfully created Goodie: PerldocCheatSheet

All of the logic for the instant answer is in PerldocCheatSheet.pm, and duckpan has already created a good skeleton:

package DDG::Goodie::PerldocCheatSheet;
# ABSTRACT: Write an abstract here
# Start at https://duck.co/duckduckhack/goodie_overview if you are new
# to instant answer development

use DDG::Goodie;

zci answer_type => "perldoc_cheat_sheeet";
zci is_cached   => 1;

# Metadata.  See https://duck.co/duckduckhack/metadata for help in filling out this section.
name "PerldocCheatSheeet";
description "Succinct explanation of what this instant answer does";
primary_example_queries "first example query", "second example query";
secondary_example_queries "optional -- demonstrate any additional triggers";
# Uncomment and complete: https://duck.co/duckduckhack/metadata#category
# category "";
# Uncomment and complete: https://duck.co/duckduckhack/metadata#topics
# topics "";
code_url "https://github.com/duckduckgo/zeroclickinfo-goodies/blob/master/lib/DDG/Goodie/PerldocCheatSheet.pm";
attribution github => ["GitHubAccount", "Friendly Name"],
            twitter => "twitterhandle";

# Triggers
triggers any => "triggerWord", "trigger phrase";

# Handle statement
handle remainder => sub {

    # optional - regex guard
    # return unless qr/^\w+/;

    return unless $_; # Guard against "no answer"

    return $_;


I’ll fill in the answers for the abstract, metadata and triggers, and the handle subroutine:

package DDG::Goodie::PerldocCheatSheet;
# ABSTRACT: A cheat sheet for perldoc, the Perl documentation program

use DDG::Goodie;

zci answer_type => "perldoc_cheat_sheet";
zci is_cached   => 1;

# Metadata
name "PerldocCheatSheet";
source "http://perltricks.com/article/155/2015/2/26/Hello-perldoc--productivity-booster";
description "A cheat sheet for perldoc, the Perl documentation program";
primary_example_queries "help perldoc", "perldoc cheatsheet", "perldoc commands", "perldoc ref";
category "programming";
topics qw/computing geek programming sysadmin/;
attribution github  => ["dnmfarrell", "David Farrell"],
            twitter => "perltricks",
            web     => 'http://perltricks.com';

# Triggers
triggers startend => (
        "perldoc help",
        "help perldoc",
        "perldoc cheat sheet",
        "perldoc cheatsheet",
        "perldoc commands",
        "perldoc ref");

# Handle statement
my $HTML = share("perldoc_cheat_sheet.html")->slurp(iomode => '<:encoding(UTF-8)');
my $TEXT= share("perldoc_cheat_sheet.txt")->slurp(iomode => '<:encoding(UTF-8)');

handle remainder => sub {
        heading => 'Perldoc Cheat Sheet',
        html    => $HTML,
        answer  => $TEXT,


The handle subroutine will return a plain text and an HTML version of the cheat sheet to the user. The share function loads static files from the share/goodie/ directory. These files should be created in the share/goodie/perldoc_cheat_sheet/ directory, and it is essential that the filenames are lowercased versions of the instant answer name, separated by underscores. So “PerldocCheatSheet” becomes “perldoc_cheat_sheet”. You can view the files on GitHub. Note that the CSS file is not referenced directly by any code: it is automagically loaded by DuckDuckGo (this is why the directory and filename must be correct). I copied the CSS from the tmux example, it provides two columns of text that will display side-by-side or wrap to a single column if the screen width is too narrow.

Testing the instant answer

The quickest way to test that the instant answer is working, is with the duckpan query command. I can run it in the terminal:

$ duckpan query

This launches an interactive command line program. I can enter one of the triggers for my perldoc instant answer, and see if the server responds as expected:

Query: perldoc ref
  You entered: perldoc ref
DDG::ZeroClickInfo  {
    Parents       WWW::DuckDuckGo::ZeroClickInfo
    public methods (4) : DOES, has_structured_answer, new, structured_answer
    private methods (0)
    internals: {
        answer        "perldoc [option]

Module Options

Looking good! (I’ve cut the output as it’s verbose). The next thing I can try is a browser test using duckpan server:

$ duckpan server

Then I point my browser at http://localhost:5000, and enter a trigger query for the instant answer. That works as well. Finally, I need to complete a unit test script for the instant answer. I’ve already got a skeleton test script which was created by duckpan new at the start:

#!/usr/bin/env perl

use strict;
use warnings;
use Test::More;
use DDG::Test::Goodie;

zci answer_type => "perldoc_cheat_sheet";
zci is_cached   => 1;

    [qw( DDG::Goodie::PerldocCheatSheeet )],
    # At a minimum, be sure to include tests for all:
    # - primary_example_queries
    # - secondary_example_queries
    'example query' => test_zci('query'),
    # Try to include some examples of queries on which it might
    # appear that your answer will trigger, but does not.
    'bad example query' => undef,


I’ll update the test file, and add some comments:

#!/usr/bin/env perl

use strict;
use warnings;
use Test::More;
use DDG::Test::Goodie;

zci answer_type => "perldoc_cheat_sheet";
zci is_cached   => 1;

# all responses for this goodie are the same
my @test_zci = (
  # regex for the plain text response
  qr/^perldoc \[option\].*Module Options.*Search Options.*Common Options.*Help.*$/s,
  # check the heading
  heading => 'Perldoc Cheat Sheet',
  # check the html pattern
  html    => qr#$#s,

    # name of goodie to test

    # At a minimum, be sure to include tests for all:
    # - primary_example_queries
    # - secondary_example_queries
    'help perldoc'        => test_zci(@test_zci),
    'help perldoc'        => test_zci(@test_zci),
    "perldoc"             => test_zci(@test_zci),
    "perldoc help"        => test_zci(@test_zci),
    "help perldoc"        => test_zci(@test_zci),
    "perldoc cheat sheet" => test_zci(@test_zci),
    "perldoc cheatsheet"  => test_zci(@test_zci),
    "perldoc commands"    => test_zci(@test_zci),

    # Try to include some examples of queries on which it might
    # appear that your answer will trigger, but does not.
    'perl doc help'     => undef,
    'perl documentaton' => undef,
    'perl faq'          => undef,
    'perl help'         => undef,


Most of this is easy to follow; but there are a few gotchas; @test_zci is a variable that stores the expected output from a successful trigger of the instant answer. It’s a bit of a hack: its passed to the test_zci() function which expects a scalar which matches the plain text response, followed by 2 key/pairs, one for the heading and one for the HTML response (see the docs for more detail). I can run this script at the command line:

$ prove -I t/PerldocCheatSheet.t
t/PerldocCheatSheet.t .. ok
All tests successful.
Files=1, Tests=12,  0 wallclock secs ( 0.02 usr  0.00 sys +  0.17 cusr  0.01 csys =  0.20 CPU)
Result: PASS

All the tests pass, so I’m ready to issue a pull request to the DuckDuckGo community!

Where to go for help

Whilst the DuckDuckGo tools are great, there is also good documentation available and a friendly community supporting development when you need it. I spent some time on the Gitter chatroom for the instant answers repo, and the people there were friendly and responsive (and more importantly, they have commit bits :).

This article was originally posted on PerlTricks.com.


David Farrell

David is a professional programmer who regularly tweets and blogs about code and the art of programming.

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