The A11y Machine

The A11y Machine (or a11ym for short, spelled “alym”) is an automated accessibility testing tool which crawls and tests pages of any Web application to produce detailed reports. It validates pages against the following specifications/laws:

• W3C Web Content Accessibility Guidelines (WCAG) 2.0, including A, AA and AAA levels (understanding levels of conformance),
• U.S. Section 508 legislation,
• W3C HTML5 Recommendation.

Table of contents

• Why?
• Installation
• Usage
  • List of URLs instead of crawling
  • Possible output
  • How does it work?
  • Write your custom rules
  • Watch the dashboard
• Roadmap and board
• Authors and license

Why?

If privacy matters for you, you're likely to install The A11y Machine over any SaaS services: It runs locally so you don't need to send your code somewhere, you can test all parts of your application including the ones which require an authentification (like a checkout, a back-office etc.)…

Here are some pros and cons compared to SaaS solutions:

Properties | The A11y Machine | SaaS services -----------|------------------|--------------- Can run locally | yes | no Can test each patch | yes | no (except if deployed) Reduce the test loop | yes | no (the loop is longer) Can test private code | yes | no (you must send your code) Can test auth-required parts | yes | no Can crawl all your pages | yes | yes (but it can be pricey)

Accessibility is not only a concern for disabled people. Bots can be considered as such, like DuckDuckGo, Google or Bing. By respecting these standards, you're likely to have a better ranking. Also it helps to clean your code. Accessibility issues are often left unaddressed for budget reasons. In fact most of the cost is spent looking for errors on your website. The A11y Machine greatly help with this task, you can thus focus on fixing your code and reap the benefits.

Installation

NPM is required. Then, execute the following lines:

$ npm install -g the-a11y-machine

If you would like to validate your pages against the HTML5 recommendation, then you need to install Java.

As an alternative you can run a Docker image instead, which will ensure the image is available locally:

$ docker build -t liip/the-a11y-machine .
$ docker run liip/the-a11y-machine --help

To get access to a report you will need to:

• Mount a path into the container,
• Specifify that internal path in your a11ym CLI options.

For example:

$ docker run -v $PWD:/var/output liip/the-a11y-machine -o /var/output http://example.org

Usage

As a prelude, see the help:

  Usage: a11ym [options] url …

  Options:

    -h, --help                                 output usage information
    -b, --bootstrap <path>                     Bootstrap file, i.e. the configuration file. All CLI options will overwrite options defined in the configuration file.
    -e, --error-level <error_level>            Minimum error level: In ascending order, `notice` (default), `warning`, and `error` (e.g. `warning` includes all warnings and errors).
    -c, --filter-by-codes <codes>              Filter results by comma-separated WCAG codes (e.g. `H25,H91,G18`).
    -C, --exclude-by-codes <codes>             Exclude results by comma-separated WCAG codes (e.g. `H25,H91,G18`).
    -d, --maximum-depth <depth>                Explore up to a maximum depth (hops).
    -m, --maximum-urls <maximum_urls>          Maximum number of URLs to compute.
    -o, --output-directory <output_directory>  Output directory.
    -r, --report <report>                      Report format: `cli`, `csv`, `html` (default), `json` or `markdown`.
    -s, --standards <standards>                Standard to use: `WCAG2A`, `WCAG2AA` (default), ` WCAG2AAA`, `Section508`, `HTML` or your own (see `--sniffers`). `HTML` can be combined with any other by a comma.
    -S, --sniffers <sniffers>                  Path to the sniffers file, e.g. `resource/sniffers.js` (default).
    -u, --filter-by-urls <urls>                Filter URL to test by using a regular expression without delimiters (e.g. 'news|contact').
    -U, --exclude-by-urls <urls>               Exclude URL to test by using a regular expression without delimiters (e.g. 'news|contact').
    -w, --workers <workers>                    Number of workers, i.e. number of URLs computed in parallel.
    --http-auth-user <http_auth_user>          Username to authenticate all HTTP requests.
    --http-auth-password <http_auth_password>  Password to authenticate all HTTP requests.
    --http-tls-disable                         Disable TLS/SSL when crawling or downloading pages.
    -V, --no-verbose                           Make the program silent.

Thus, the simplest use is to run a11ym with a URL:

$ ./a11ym http://example.org/

All URLs accessible from http://example.org/ will be tested against the WCAG2AA standard. See the --maximum-urls options to reduce the number of URLs to test.

Then open a11ym_output/index.html and browser the result!

List of URLs instead of crawling

You can compute several URLs by adding them to the command-line, like this:

$ ./a11ym http://example.org/A http://example.org/B http://example.org/C

Alternatively, this is possible to read URLs from STDIN, as follows:

$ cat URLs.lists | ./a11ym -

Note the -: It means “Read URLs from STDIN please”.

When reading several URLs, the --maximum-depth option will be forced to 1.

Possible output

The index of the reports:

Report of a specific URL:

The dashboard of all reports:

Selecting standards

As mentionned, the following standards are supported:

• W3C WCAG,
• U.S. Section 508 legislation,
• W3C HTML5 recommendation.

You cannot combine standards between each other, except HTML5 that can be combined with any other. So for instance, to run WCAG2AAA:

$ ./a11ym --standards WCAG2AAA http://example.org/

To run WCAG2AA along with HTML:

$ ./a11ym --standards WCAG2AA,HTML http://example.org/

How does it work?

The pipe looks like this:

1. The node-simplecrawler tool is used to crawl a Web application based on the given URLs, with our own specific exploration algorithm to provide better results quickly, in addition to support parallelism,
2. For each URL found, 2 kind of tests are applied:
   1. Accessibility: PhantomJS runs and HTML_CodeSniffer is injected in order to check the page conformance; This step is semi-automated by the help of pa11y, which is a very thin layer of code wrapping PhantomJS and HTML_CodeSniffer,
   2. HTML: The Nu Html Checker (v.Nu) is run on the same URL.
3. Finally, results from different tools are normalized, and enhanced and easy to use reports are produced.

PhantomJS and HTML_CodeSniffer are widely-used, tested and precise tools. pa11y simplifies the use of these two latters. The Nu Html Checker is the tool used by the W3C to validate documents online. However, in this case, we do all validations offline! Nothing is sent over the network. Again, privacy.

Write your custom rules

HTML_CodeSniffer is build in a way that allows you to extend existing rules or write your own. A rule is represented as a sniffer (this is another terminology). The resource/sniffers/ directory contains an example of a custom sniffer.

The A11y Machine comes with a default file containing all the sniffers: resource/sniffers.js. You can provide your own by using the --sniffers option. To build your own sniffers, simply copy the resource/sniffers/ somewhere as a basis, complete it, then compile it with the a11ym-sniffers utility:

$ ./a11ym-sniffers --directory my/sniffers/ --output-directory my_sniffers.js

Then, to effectively use it:

$ ./a11ym --sniffers my_sniffers.js --standard MyStandard http://example.org/

Watch the dashboard

Run the a11ym-dashboard command to serve the dashboard. The dashboard is an overview of several reports generated by the a11ym command. The command can serves the dashboard over HTTP, or over static files. In addition to requiring a root directory, it requires: In the first case, an address, and a port, in the second, nothing more than just a flag. For instance, if the reports are generated with the following command:

$ ./a11ym --output-directory my_reports/`date +%s`/ http://example.org/A http://example.org/B

Then, the root directory is my_reports/ and thus the dashboard will be started over HTTP with the following command:

$ ./a11ym-dashboard --root my_reports

Browse 127.0.0.1:8080 (by default) to see the dashboard!

Or to generate static files:

$ ./a11ym-dashboard --root my_reports --static-output

Open my_reports/index.html, and do the same!

Bonus: Use the --open option to automatically open the dashboard in your favorite browser.

Roadmap and board

The roadmap is public:

• See the incoming milestones,
• See the in progress issues.

The board is publicly available at the following URL: https://waffle.io/liip/TheA11yMachine.

Authors and license

Original author is Ivan Enderlin, accompagnied by Gilles Crettenand and David Jeanmonod. This software is backed by Liip.

BSD-3-Clause:

Copyright (c), Ivan Enderlin and Liip All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.