Running Tests from the Local System

The tests are designed to be run from your local computer.

System Setup

The test environment requires Python 2.7+ (but not Python 3.x).

On Windows, be sure to add the Python directory (c:\python2x, by default) to your %Path% Environment Variable, and read the Windows Notes section below.

Install pip. On many systems, this can be achieved with the command python -m ensurepip. If this is not possible, use your system’s package manager to install the python-pip package.

Next, install virtualenv using the following command:

pip install virtualenv

To get the tests running, you need to set up the test domains in your hosts file.

The necessary content can be generated with ./wpt make-hosts-file; on Windows, you will need to preceed the prior command with python or the path to the Python binary (python wpt make-hosts-file).

For example, on most UNIX-like systems, you can setup the hosts file with:

./wpt make-hosts-file | sudo tee -a /etc/hosts

And on Windows (this must be run in a PowerShell session with Administrator privileges):

python wpt make-hosts-file | Out-File %SystemRoot%\System32\drivers\etc\hosts -Encoding ascii -Append

If you are behind a proxy, you also need to make sure the domains above are excluded from your proxy lookups.

The Ahem font is used to test precise rendering behavior. This font should be loaded as a web font in tests, using the /fonts/ahem.css stylesheet, as follows:

<link rel="stylesheet" type="text/css" href="/fonts/ahem.css" />

Windows Notes

Generally Windows Subsystem for Linux will provide the smoothest user experience for running web-platform-tests on Windows.

The standard Windows shell requires that all wpt commands are prefixed by the Python binary i.e. assuming python is on your path the server is started using:

python wpt serve

Via the browser

The test environment can then be started using

./wpt serve

This will start HTTP servers on two ports and a websockets server on one port. By default the web servers start on ports 8000 and 8443 and the other ports are randomly-chosen free ports. Tests must be loaded from the first HTTP server in the output. To change the ports, create a config.json file in the wpt root directory, and add port definitions of your choice e.g.:

  "ports": {
    "http": [1234, "auto"],

After your hosts file is configured, the servers will be locally accessible at:

https://web-platform.test:8443/ *

To use the web-based runner point your browser to:

https://web-platform.test:8443/tools/runner/index.html *

This server has all the capabilities of the publicly-deployed version–see Running the Tests from the Web.

*See Trusting Root CA

Via the command line

Many tests can be automatically executed in a new browser instance using

./wpt run [browsername] [tests]

This will automatically load the tests in the chosen browser and extract the test results. For example to run the dom/historical.html tests in a local copy of Chrome:

./wpt run chrome dom/historical.html

Or to run in a specified copy of Firefox:

./wpt run --binary ~/local/firefox/firefox firefox dom/historical.html

For details on the supported products and a large number of other options for customising the test run:

./wpt run --help

A complete listing of the command-line arguments is available here.

Additional browser-specific documentation: