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
- W3C Web Content Accessibility Guidelines
(WCAG) 2.0, including A, AA and AAA levels (understanding levels of
- U.S. Section 508 legislation,
- W3C HTML5 Recommendation.
Table of contents
- Roadmap and board
- Authors and license
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.
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
$ docker run -v $PWD:/var/output liip/the-a11y-machine -o /var/output http://example.org
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. --ignore-robots-txt Ignore robots.txt file.
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.
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 -
-: It means “Read URLs from STDIN please”.
When reading several URLs, the
--maximum-depth option will be forced to 1.
The index of the reports:
Report of a specific URL:
The dashboard of all reports:
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
$ ./a11ym --standards WCAG2AAA http://example.org/
WCAG2AA along with
$ ./a11ym --standards WCAG2AA,HTML http://example.org/
How does it work?
The pipe looks like this:
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,
- For each URL found, 2 kind of tests are applied:
- Finally, results from different tools are normalized, and enhanced and easy
to use reports are produced.
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
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
option. To build your own sniffers, simply copy the
somewhere as a basis, complete it, then compile it with the
$ ./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
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
127.0.0.1:8080 (by default) to see the dashboard!
Or to generate static files:
$ ./a11ym-dashboard --root my_reports --static-output
my_reports/index.html, and do the same!
Bonus: Use the
--open option to automatically open the dashboard in your
Roadmap and board
The roadmap is public:
The board is publicly available at the following URL: https://waffle.io/liip/TheA11yMachine.
Authors and license
Copyright (c), Ivan Enderlin and Liip
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