Icelandic crossword game website
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Netskrafl - an Icelandic crossword game website

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English summary

This repository contains the implementation of an Icelandic crossword game inspired by SCRABBLE(tm). The game, which is free-to-play, is accessible on the web at and

Screenshot from mobile UI

The game backend is implemented in Python 2.7 for Google App Engine but the core code is also compatible with Python 3.x and PyPy.

The frontend is a tablet- and smartphone-friendly web client in HTML5 and JavaScript connecting via Ajax to a Flask-based web server on the backend.

The game contains a robot crossword player written in Python. The algorithm is based on Appel & Jacobson's classic paper "The World's Fastest Scrabble Program". At maximum strength level, the robot always plays the highest-scoring move possible but additional and alternative strategies can be plugged in relatively easily. At the lowest strength level, the robot is limited to a set of common words, about a quarter of the size of the entire word database.

The software has a range of features such as immediate tile-by-tile feedback on word validity and score, real-time synchronized games with clocks, Elo scoring of players, an online chat window, and the ability to view player track records.

The game uses a word database encoded in a Directed Acyclic Word Graph (DAWG). For Icelandic, the graph contains almost 2.3 million word forms. Further information about the DAWG implementation can be found in in the Skrafl repository on GitHub.

The game mechanics are mostly found in

The robot player is implemented in

The DAWG navigation code is in

Particulars to the Icelandic language are found in

The main Flask web server is in

The Game and User classes are found in

The persistence layer, using the schemaless App Engine NDB database, is in

The client JavaScript code is in static/netskrafl.js.

The various Flask HTML templates are found in templates/*.html.

The word database is in resources/ordalisti.text.dawg.

To build and run locally

Follow these steps:

  1. Install Python 2.7, possibly in a virtualenv.

  2. Download the Google App Engine SDK (GAE) for Python and follow the installation instructions.

  3. git clone to your GAE application directory.

  4. Run pip install -t lib -r requirements.txt to install required Python packages so that they are accessible to GAE.

  5. Run python to generate the DAWG *.pickle files. This takes a couple of minutes.

  6. Create a secret session key for Flask in resources/secret_key.bin (see How to generate good secret keys, you need to scroll down to find the heading).

  7. Install Node.js if you haven't already. Run npm install to install Node dependencies.

  8. In a separate terminal window, but in the Netskrafl directory, run grunt make. Then run grunt to start watching changes of js and css files.

  9. Run either runserver.bat or

Or, alternatively:

Run ./ (tested on Debian based Linux and OS X).

Generating a new vocabulary file

To generate a new vocabulary file (ordalistimax15.sorted.txt), assuming you already have the BÍN database in PostgreSQL (here in table ord), invoke psql, log in to your database and create the following views:

create or replace view isl as
	select stofn, utg, ordfl, fl, ordmynd, beyging from ord
  	where ordmynd ~ '^[aábdðeéfghiíjklmnoóprstuúvxyýþæö]+$';

create or replace view disl as
	select distinct ordmynd from isl
	where fl not in ('fyr','örn','ffl','bibl') and length(ordmynd) > 2 and length(ordmynd) <= 15
	order by ordmynd;

Then, to generate the vocabulary file from the psql command line:

\copy (select * from disl) to '/home/username/github/Netskrafl/resources/ordalistimax15.sorted.txt';

Original Author

Vilhjálmur Þorsteinsson, Reykjavík, Iceland.

Contact me via GitHub for queries or information regarding Netskrafl.

Please contact me if you have plans for using Netskrafl as a basis for your own game website and prefer not to operate under the conditions of the GNU GPL v3 license (see below).


Netskrafl - an Icelandic crossword game website

Copyright (C) 2017 Miðeind ehf.

This set of programs is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This set of programs is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

The full text of the GNU General Public License is available here:


SCRABBLE is a registered trademark. This software or its author are in no way affiliated with or endorsed by the owners or licensees of the SCRABBLE trademark.