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Pa11y is your automated accessibility testing pal. It runs HTML CodeSniffer from the command line for programmatic accessibility reporting.

NPM version Node.js version support Build status Dependencies LGPL-3.0 licensed

On the command line:


In JavaScript:

var pa11y = require('pa11y');
var test = pa11y(options);'', function (error, results) {
    /* ... */

✨ 🔜 ✨ The Pa11y team is very excited to announce plans for the successor to Pa11y Dashboard and Pa11y Webservice, codename "Sidekick". Help us define the features that you want to see by visiting the proposal. ✨

Table Of Contents


Pa11y requires Node.js 4+ to run.


On a Mac, you can install the required dependency with Homebrew:

$ brew install node

Alternatively download pre-built packages from the Node.js website.


Depending on your flavour of Linux, you should be able to use a package manager to install the required dependency. Alternatively download pre-built packages from the Node.js website.


On Windows 10, download a pre-built package from the Node.js website. Pa11y will be usable via the bundled Node.js application as well as the Windows command prompt.

Windows 7 and below users approach with caution – we've been able to get Pa11y running but only after installing Visual Studio and the Windows SDK (as well as Git, and Python). The Windows installation instructions for node-gyp are a good place to start. If you have had a better experience than this then please do share!

Command-Line Interface

Install Pa11y globally with npm:

npm install -g pa11y

This installs the pa11y command-line tool:

Usage: pa11y [options] <url>
    -h, --help                     output usage information
    -V, --version                  output the version number
    -n, --environment              output details about the environment Pa11y will run in
    -s, --standard <name>          the accessibility standard to use: Section508, WCAG2A, WCAG2AA (default), WCAG2AAA
    -r, --reporter <reporter>      the reporter to use: cli (default), csv, tsv, html, json
    -l, --level <level>            the level of message to fail on (exit with code 2): error, warning, notice
    -T, --threshold <number>       permit this number of errors, warnings, or notices, otherwise fail with exit code 2
    -i, --ignore <ignore>          types and codes of messages to ignore, a repeatable value or separated by semi-colons
    -R, --root-element <selector>  a CSS selector used to limit which part of a page is tested
    -E, --hide-elements <hide>     a CSS selector to hide elements from testing, selectors can be comma separated
    -c, --config <path>            a JSON or JavaScript config file
    -p, --port <port>              the port to run PhantomJS on
    -t, --timeout <ms>             the timeout in milliseconds
    -w, --wait <ms>                the time to wait before running tests in milliseconds
    -v, --verify-page <string>     HTML string to verify is present in the page source HTML
    -d, --debug                    output debug messages
    -H, --htmlcs <url>             the URL or path to source HTML_CodeSniffer from
    -e, --phantomjs <path>         the path to the phantomjs executable
    -S, --screen-capture <path>    a path to save a screen capture of the page to
    -A, --add-rule <rule>          WCAG 2.0 rules from a different standard to include, a repeatable value or separated by semi-colons

Running Tests

Run an accessibility test against a URL:


Run an accessibility test against a file (absolute paths only, not relative):

pa11y file:///path/to/your/file.html

Run a test with CSV reporting and save to a file:

pa11y --reporter csv > report.csv

Run a test with TSV reporting and save to a file:

pa11y --reporter tsv > report.tsv

Run Pa11y with the Section508 ruleset:

pa11y --standard Section508

Exit Codes

The command-line tool uses the following exit codes:

  • 0: Pa11y ran successfully, and there are no errors
  • 1: Pa11y failed run due to a technical fault
  • 2: Pa11y ran successfully but there are errors in the page

By default, only accessibility issues with a type of error will exit with a code of 2. This is configurable with the --level flag which can be set to one of the following:

  • error: exit with a code of 2 on errors only, exit with a code of 0 on warnings and notices
  • warning: exit with a code of 2 on errors and warnings, exit with a code of 0 on notices
  • notice: exit with a code of 2 on errors, warnings, and notices
  • none: always exit with a code of 0

Command-Line Configuration

The command-line tool can be configured with a JSON file as well as arguments. By default it will look for a pa11y.json file in the current directory, but you can change this with the --config flag:

pa11y --config ./path/to/config.json

For more information on configuring Pa11y, see the configuration documentation.


The ignore flag can be used in several different ways. Separated by semi-colons:

pa11y --ignore "warning;notice"

or by using the flag multiple times:

pa11y --ignore warning --ignore notice

Pa11y can also ignore notices, warnings, and errors up to a threshold number. This might be useful if you're using CI and don't want to break your build. The following example will return exit code 0 on a page with 9 errors, and return exit code 2 on a page with 11 errors.

pa11y --threshold 10


The command-line tool can report test results in a few different ways using the --reporter flag. The built-in reporters are:

  • cli: output test results in a human-readable format
  • csv: output test results as comma-separated values
  • tsv: output test results as tab-separated values
  • html: output test results as an HTML document
  • json: output test results as a JSON array
  • markdown: output test results as a Markdown document

You can also write and publish your own reporters. Pa11y looks for reporters in the core library, your node_modules folder (with a naming pattern), and the current working directory. The first reporter found will be loaded. So with this command:

pa11y --reporter rainbows

The following locations will be checked:


A Pa11y reporter should export the following methods, and these should make use of console to send output:

begin(url); // Called when pa11y starts 
error(message); // Called when a technical error is reported 
debug(message); // Called when a debug message is reported 
info(message); // Called when an information message is reported 
results(resultsArray, url); // Called with the results of a test run 

Reporters may also optionally export a process method. This should accept the same arguments as the results method but return the processed results rather than outputting them:

process(resultsArray, url); // Called with results by a user 

You may find the following reporters useful:

  • 1.0-json: output test results in the Pa11y 1.0 JSON format

JavaScript Interface

Install Pa11y with npm or add to your package.json:

npm install pa11y

Require Pa11y:

var pa11y = require('pa11y');

Create a tester by initialising Pa11y with some options:

var test = pa11y(options);

The function can then be used to run your test function against a URL:'', function(error, results) {
    // ... 

The results that get passed into your test callback come from HTML CodeSniffer, and look like this:

        code: 'WCAG2AA.Principle1.Guideline1_1.1_1_1.H30.2',
        context: '<a href=""><img src="example.jpg" alt=""/></a>',
        message: 'Img element is the only content of the link, but is missing alt text. The alt text should describe the purpose of the link.',
        selector: 'html > body > p:nth-child(1) > a',
        type: 'error',
        typeCode: 1
        code: 'WCAG2AA.Principle1.Guideline1_3.1_3_1.H49.B',
        context: '<b>Hello World!</b>',
        message: 'Semantic markup should be used to mark emphasised or special text so that it can be programmatically determined.',
        selector: '#content > b:nth-child(4)',
        type: 'warning',
        typeCode: 2
        code: 'WCAG2AA.Principle2.Guideline2_4.2_4_4.H77,H78,H79,H80,H81',
        context: '<a href="">Hello World!</a>',
        message: 'Check that the link text combined with programmatically determined link context identifies the purpose of the link.',
        selector: 'html > body > ul > li:nth-child(2) > a',
        type: 'notice',
        typeCode: 3

If you wish to transform these results with the command-line reporters, then you can do so in your code by requiring them in. The csv, tsv, html, json, and markdown reporters all expose a process method:

// Assuming you've already run tests, and the results 
// are available in a `results` variable: 
var htmlReporter = require('pa11y/reporter/html');
var html = htmlReporter.process(results, url);

Validating Actions

Pa11y exposes a function which allows you to validate action strings before attempting to use them.

This function accepts an action string and returns a boolean indicating whether it matches one of the actions that Pa11y supports:

pa11y.validateAction('click element #submit');  // true 
pa11y.validateAction('open the pod bay doors'); // false 


Pa11y has lots of options you can use to change the way PhantomJS runs, or the way your page is loaded. Options can be set either on the Pa11y instance when it's created or the individual test runs. This allows you to set some defaults which can be overridden per-test:

// Set the default Foo header to "bar" 
var test = pa11y({
    page: {
        headers: {
            Foo: 'bar'
// Run a test with the Foo header set to "bar"'', function(error, results) { /* ... */ });
// Run a test with the Foo header overridden'', {
    page: {
        headers: {
            Foo: 'hello'
}, function(error, results) { /* ... */ });

Below is a reference of all the options that are available:

actions (array) BETA

Actions to be run before Pa11y tests the page. There are quite a few different actions available in Pa11y, the Actions documentation outlines each of them.

Note: actions are currently in a beta state and the API may change while we gather feedback.

    actions: [
        'set field #username to exampleUser',
        'set field #password to password1234',
        'click element #submit',
        'wait for path to be /myaccount'

Defaults to an empty array.

allowedStandards (array)

The accessibility standards that are allowed to be used. This can be modified to allow for custom HTML CodeSniffer standards.

    allowedStandards: ['WCAG2AA', 'My Custom Standard']

Defaults to Section508, WCAG2A, WCAG2AA, and WCAG2AAA.

beforeScript (function)

Note: unless you're doing something particularly complicated, it's much easier and less error prone to use actions rather than beforeScript. If you specify both, the beforeScript will be dropped with a warning.

A function to be run before Pa11y tests the page. The function accepts three parameters:

    beforeScript: function(page, options, next) {
        // Make changes to the page 
        // When finished call next to continue running Pa11y tests 

Defaults to null.

hideElements (string)

A CSS selector to hide elements from testing, selectors can be comma separated. Elements matching this selector will be hidden from testing by styling them with visibility:hidden.

    hideElements: '.advert, #modal, div[aria-role=presentation]'

htmlcs (string)

The path or URL to source HTML CodeSniffer from.

    htmlcs: ''

Defaults to a local copy of HTML CodeSniffer, found in lib/vendor/HTMLCS.js.

ignore (array)

An array of result codes and types that you'd like to ignore. You can find the codes for each rule in the console output and the types are error, warning, and notice.

    ignore: [

Defaults to an empty array.

log (object)

An object which implements the methods debug, error, and info which will be used to report errors and test information.

    log: {
        debug: console.log.bind(console),
        error: console.error.bind(console),

Each of these defaults to an empty function.

page.headers (object)

A key-value map of request headers to send when testing a web page.

    page: {
        headers: {
            Cookie: 'foo=bar'

Defaults to an empty object.

page.settings (object)

A key-value map of settings to add to the PhantomJS page. For a full list of available settings, see the PhantomJS page settings documentation.

    page: {
        settings: {
            loadImages: false,
            userName: 'nature',
            password: 'say the magic word'

Defaults to:

    userAgent: 'pa11y/<version> (truffler/<version>)'

page.viewport (object)

The viewport width and height in pixels. The viewport object must have both width and height properties.

    page: {
        viewport: {
            width: 320,
            height: 480

Defaults to:

    width: 1024,
    height: 768

phantom (object)

A key-value map of settings to initialise PhantomJS with. This is passed directly into the phantom module – documentation can be found here. You can pass PhantomJS command-line parameters in the phantom.parameters option as key-value pairs.

    phantom: {
        port: 1234,
        parameters: {
            'ignore-ssl-errors': 'false',
            'ssl-protocol': 'tlsv1'

Defaults to:

    parameters: {
        'ignore-ssl-errors': 'true'

If phantom.port is not specified, a random available port will be used.

rootElement (element)

The root element for testing a subset of the page opposed to the full document.

    rootElement: '#main'

Defaults to null, meaning the full document will be tested.

rules (array)

An array of WCAG 2.0 guidelines that you'd like to include to the current standard. Note: THese won't be applied to Section508 standard. You can find the codes for each guideline in the HTML Code Sniffer WCAG2AAA ruleset .

    rules: [

screenCapture (string)

A file path to save a screen capture of the tested page to. The screen will be captured immediately after the Pa11y tests have run so that you can verify that the expected page was tested.

    screenCapture: __dirname + '/my-screen-capture.png'

Defaults to null, meaning the screen will not be captured.

standard (string)

The accessibility standard to use when testing pages. This should be one of Section508, WCAG2A, WCAG2AA, or WCAG2AAA (or match one of the standards in the allowedStandards option).

    standard: 'Section508'

Defaults to WCAG2AA.

timeout (number)

The time in milliseconds that a test should be allowed to run before calling back with a timeout error.

    timeout: 500

Defaults to 30000.

wait (number)

The time in milliseconds to wait before running HTML CodeSniffer on the page.

    wait: 500

Defaults to 0.

verifyPage (string)

HTML string to verify is present in the page source HTML. Could be used to ascertain that intended page is being tested (as opposed to error page) by using <title> tags and content (as below), or that a specific element is present.

    verifyPage: '<title>Nature Research: science journals, jobs, information and services.</title>'

Defaults to null.


Actions are additional interactions that you can make Pa11y perform before the tests are run. They allow you to do things like click on a button, enter a value in a form, wait for a redirect, or wait for the URL fragment to change:

    actions: [
        'click element #tab-1',
        'set field #fullname to John Doe',
        'check field #terms-and-conditions',
        'uncheck field #subscribe-to-marketing',
        'wait for fragment to be #page-2',
        'wait for path to not be /login',
        'wait for url to be'

Below is a reference of all the available actions and what they do on the page. Some of these take time to complete so you may need to increase the timeout option if you have a large set of actions.

Click Element

This allows you to click an element by passing in a CSS selector. This action takes the form click element <selector>. E.g.

    actions: [
        'click element #tab-1'

You can use any valid query selector, including classes and types.

Set Field Value

This allows you to set the value of a text-based input or select box by passing in a CSS selector and value. This action takes the form set field <selector> to <value>. E.g.

    actions: [
        'set field #fullname to John Doe'

Check/Uncheck Field

This allows you to check or uncheck checkbox and radio inputs by passing in a CSS selector. This action takes the form check field <selector> or uncheck field <selector>. E.g.

    actions: [
        'check field #terms-and-conditions',
        'uncheck field #subscribe-to-marketing'

Wait For Fragment/Path/URL

This allows you to pause the test until a condition is met, and the page has either a given fragment, path, or URL. This will wait until Pa11y times out so it should be used after another action that would trigger the change in state. You can also wait until the page does not have a given fragment, path, or URL using the to not be syntax. This action takes one of the forms:

  • wait for fragment to be <fragment> (including the preceding #)
  • wait for fragment to not be <fragment> (including the preceding #)
  • wait for path to be <path> (including the preceding /)
  • wait for path to not be <path> (including the preceding /)
  • wait for url to be <url>
  • wait for url to not be <url>


    actions: [
        'wait for path to be /login'


Basic Example

Run Pa11y on a URL and output the results. See the example, or run it with:

node example/basic

Multiple Example

Use async to run Pa11y on multiple URLs in series, and output the results. See the example, or run it with:

node example/multiple

Multiple Concurrent Example

Use async to run Pa11y on multiple URLs in parallel, with a configurable concurrency. Then output the results. See the example, or run it with:

node example/multiple-concurrent

Actions Example

Step through some actions before Pa11y runs. This example logs into a fictional site then waits until the account page has loaded before running Pa11y. See the example.

Before Script Example

Inject a script before Pa11y runs. This example logs into a fictional site then waits until the account page has loaded before running Pa11y. See the example.

Common Questions and Troubleshooting

See our Troubleshooting guide to get the answers to common questions about Pa11y, along with some ideas to help you troubleshoot any problems.


There are many ways to contribute to Pa11y, we cover these in the contributing guide for this repo.

If you're ready to contribute some code, clone this repo locally and commit your code on a new branch.

Please write unit tests for your code, and check that everything works by running the following before opening a PR:

make ci

You can also run verifications and tests individually:

make verify              # Verify all of the code (ESLint) 
make test                # Run all tests 
make test-unit           # Run the unit tests 
make test-unit-coverage  # Run the unit tests with coverage 
make test-integration    # Run the integration tests 

Support and Migration

Pa11y major versions are normally supported for 6 months after their last minor release. This means that patch-level changes will be added and bugs will be fixed. The table below outlines the end-of-support dates for major versions, and the last minor release for that version.

We also maintain a migration guide to help you migrate.

Major Version Last Minor Release Node.js Versions Support End Date
❤️ 4 N/A 4+ N/A
💀 3 3.8 0.12–6 2016-12-05
💀 2 2.4 0.10–0.12 2016-10-16
💀 1 1.7 0.10 2016-06-08

If you're opening issues related to these, please mention the version that the issue relates to.


Pa11y is licensed under the Lesser General Public License (LGPL-3.0).
Copyright © 2013–2017, Team Pa11y