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Poltergeist - A PhantomJS driver for Capybara

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Poltergeist is a driver for Capybara. It allows you to run your Capybara tests on a headless PhantomJS browser. If you would like to run your tests on headless Chrome there's another project Cuprite claims to be compatible with Poltergeist.

If you're viewing this at, you're reading the documentation for the master branch. View documentation for the latest release (1.18.1).

Getting help

Questions should be posted on Stack Overflow, using the 'poltergeist' tag.

Bug reports should be posted on GitHub (and be sure to read the bug reporting guidance below).


Add this line to your Gemfile and run bundle install:

gem 'poltergeist'

In your test setup add:

require 'capybara/poltergeist'
Capybara.javascript_driver = :poltergeist

If you were previously using the :rack_test driver, be aware that your app will now run in a separate thread and this can have consequences for transactional tests. See the Capybara README for more detail.

Installing PhantomJS

You need at least PhantomJS 1.8.1. There are no other external dependencies (you don't need Qt, or a running X server, etc.)


  • Homebrew: brew tap homebrew/cask && brew cask install phantomjs
  • MacPorts: sudo port install phantomjs
  • Manual install: Download this


  • Download the 32 bit or 64 bit binary.
  • Extract the tarball and copy bin/phantomjs into your PATH

DO NOT use phantomjs from the official Ubuntu repositories, since it doesn't work well with poltergeist. More information here.


Manual compilation

Do this as a last resort if the binaries don't work for you. It will take quite a long time as it has to build WebKit.

(See also the PhantomJS building guide.)


Poltergeist runs on MRI 1.9+, JRuby 1.9+ and Rubinius 1.9+. Poltergeist and PhantomJS are currently supported on Mac OS X, Linux, and Windows platforms.

Ruby 1.8 is no longer supported. The last release to support Ruby 1.8 was 1.0.2, so you should use that if you still need Ruby 1.8 support.

PhantomJS does not support ES6 features at the time of writing this document. Setting js_errors to true can help determine if failing tests require Polyfills, although a bug in PhantomJS can cause silent failures if using ES6 features like let, const, etc.

Running on a CI

There are no special steps to take. You don't need Xvfb or any running X server at all.

Travis CI, CircleCI, Codeship and Semaphore have PhantomJS pre-installed.

Depending on your tests, one thing that you may need is some fonts. If you're getting errors on a CI that don't occur during development then try taking some screenshots - it may well be missing fonts throwing things off kilter. Your distro will have various font packages available to install.

What's supported?

Poltergeist supports all the mandatory features for a Capybara driver, and the following optional features:

  • page.evaluate_script and page.execute_script
  • page.within_frame
  • page.status_code
  • page.response_headers
  • page.save_screenshot
  • page.driver.render_base64(format, options)
  • page.driver.scroll_to(left, top)
  • page.driver.basic_authorize(user, password)
  • element.send_keys(*keys)
  • page.driver.set_proxy(ip, port, type, user, password)
  • window API
  • cookie handling
  • drag-and-drop

There are some additional features:

Taking screenshots with some extensions

You can grab screenshots of the page at any point by calling save_screenshot('/path/to/file.png') (this works the same way as the PhantomJS render feature, so you can specify other extensions like .pdf, .gif, etc.) Just in case you render pdf it's might be worth to set driver.paper_size= with settings provided by PhantomJS in here

By default, only the viewport will be rendered (the part of the page that is in view). To render the entire page, use save_screenshot('/path/to/file.png', :full => true).

You also have an ability to render selected element. Pass option selector with any valid CSS element selector to make a screenshot bounded by that element save_screenshot('/path/to/file.png', :selector => '#id').

If you need for some reasons base64 encoded screenshot you can simply call render_base64 that will return you encoded image. Additional options are the same as for save_screenshot except the first argument which is format (:png by default, acceptable :png, :gif, :jpeg).

Clicking precise coordinates

Sometimes its desirable to click a very specific area of the screen. You can accomplish this with, y), where x and y are the screen coordinates.

Remote debugging (experimental)

If you use the :inspector => true option (see below), remote debugging will be enabled.

When this option is enabled, you can insert page.driver.debug into your tests to pause the test and launch a browser which gives you the WebKit inspector to view your test run with.

You can register this debugger driver with a different name and set it as the current javascript driver. By example, in your helper file:

Capybara.register_driver :poltergeist_debug do |app|, :inspector => true)

# Capybara.javascript_driver = :poltergeist
Capybara.javascript_driver = :poltergeist_debug

Read more here

Manipulating request headers

You can manipulate HTTP request headers with these methods:

page.driver.headers # => {}
page.driver.headers = { "User-Agent" => "Poltergeist" }
page.driver.add_headers("Referer" => "")
page.driver.headers # => { "User-Agent" => "Poltergeist", "Referer" => "" }

Notice that headers= will overwrite already set headers. You should use add_headers if you want to add a few more. These headers will apply to all subsequent HTTP requests (including requests for assets, AJAX, etc). They will be automatically cleared at the end of the test. You have ability to set headers only for the initial request:

page.driver.headers = { "User-Agent" => "Poltergeist" }
page.driver.add_header("Referer", "", permanent: false)
page.driver.headers # => { "User-Agent" => "Poltergeist", "Referer" => "" }
page.driver.headers # => { "User-Agent" => "Poltergeist" }

This way your temporary headers will be sent only for the initial request, and related 30x redirects. All subsequent request will only contain your permanent headers. If the temporary headers should not be sent on related 30x redirects, specify permanent: :no_redirect.

Headers set with any of these methods will be set within all windows in the session, with the exception of temporary headers, which are only set within the current window.

Inspecting network traffic

You can inspect the network traffic (i.e. what resources have been loaded) on the current page by calling page.driver.network_traffic. This returns an array of request objects. A request object has a response_parts method containing data about the response chunks.

You can inspect requests that were blocked by a whitelist or blacklist by calling page.driver.network_traffic(:blocked). This returns an array of request objects. The response_parts portion of these requests will always be empty.

Please note that network traffic is not cleared when you visit new page. You can manually clear the network traffic by calling page.driver.clear_network_traffic or page.driver.reset

Manipulating cookies

The following methods are used to inspect and manipulate cookies:

  • page.driver.cookies - a hash of cookies accessible to the current page. The keys are cookie names. The values are Cookie objects, with the following methods: name, value, domain, path, secure?, httponly?, samesite, expires.
  • page.driver.set_cookie(name, value, options = {}) - set a cookie. The options hash can take the following keys: :domain, :path, :secure, :httponly, :samesite, :expires. :expires should be a Time object.
  • page.driver.remove_cookie(name) - remove a cookie
  • page.driver.clear_cookies - clear all cookies

Sending keys

There's an ability to send arbitrary keys to the element:

element = find('input#id')

or even more complicated:

element.send_keys('H', 'elo', :left, 'l') # => 'Hello'
element.send_keys(:enter) # triggers Enter key

Since it's implemented natively in PhantomJS this will exactly imitate user behavior. See more about sendEvent and PhantomJS keys


You can customize the way that Capybara sets up Poltergeist via the following code in your test setup:

Capybara.register_driver :poltergeist do |app|, options)

options is a hash of options. The following options are supported:

  • :phantomjs (String) - A custom path to the phantomjs executable
  • :debug (Boolean) - When true, debug output is logged to STDERR. Some debug info from the PhantomJS portion of Poltergeist is also output, but this goes to STDOUT due to technical limitations.
  • :logger (Object responding to puts) - When present, debug output is written to this object
  • :phantomjs_logger (IO object) - Where the STDOUT from PhantomJS is written to. This is where your console.log statements will show up. Default: STDOUT
  • :timeout (Numeric) - The number of seconds we'll wait for a response when communicating with PhantomJS. Default is 30.
  • :inspector (Boolean, String) - See 'Remote Debugging', above.
  • :js_errors (Boolean) - When false, JavaScript errors do not get re-raised in Ruby.
  • :window_size (Array) - The dimensions of the browser window in which to test, expressed as a 2-element array, e.g. [1024, 768]. Default: [1024, 768]
  • :screen_size (Array) - The dimensions the window size will be set to when Window#maximize is called. Expressed as a 2-element array, e.g. [1600, 1200]. Default: [1366, 768]
  • :phantomjs_options (Array) - Additional command line options to be passed to PhantomJS, e.g. ['--load-images=no', '--ignore-ssl-errors=yes']
  • :extensions (Array) - An array of JS files to be preloaded into the phantomjs browser. Useful for faking unsupported APIs.
  • :port (Fixnum) - The port which should be used to communicate with the PhantomJS process. Defaults to a random open port.
  • :host (String) - The name or IP of the PhantomJS host. Default is ''.
  • :url_blacklist (Array) - Default session url blacklist - expressed as an array of strings to match against requested URLs.
  • :url_whitelist (Array) - Default session url whitelist - expressed as an array of strings to match against requested URLs.
  • :page_settings (Hash) - PhantomJS web page settings (

URL Blacklisting & Whitelisting

Poltergeist supports URL blacklisting, which allows you to prevent scripts from running on designated domains:

page.driver.browser.url_blacklist = ['']

and also URL whitelisting, which allows scripts to only run on designated domains:

page.driver.browser.url_whitelist = ['']

If you are experiencing slower run times, consider creating a URL whitelist of domains that are essential or a blacklist of domains that are not essential, such as ad networks or analytics, to your testing environment.


Unfortunately, the nature of full-stack testing is that things can and do go wrong from time to time. This section aims to highlight a number of common problems and provide ideas about how you can work around them.

DeadClient errors

Sometimes PhantomJS crashes during a test. There are basically two kinds of crashes: those that can be reproduced every time, and those that occur sporadically and are not easily reproduced.

If your crash happens every time, you should read the PhantomJS crash reporting guide and file a bug against PhantomJS. Feel free to also file a bug against Poltergeist in case there are workarounds that can be implemented within Poltergeist. Also, if lots of Poltergeist users are experiencing the same crash then fixing it will move up the priority list.

If your crash is sporadic, there is less that can be done. Often these issues are very complicated and difficult to track down. It may be that the crash has already been fixed in a newer version of WebKit that will eventually find its way into PhantomJS. It's still worth reporting your bug against PhantomJS, but it's probably not worth filing a bug against Poltergeist as there's not much we can do.

If you experience sporadic crashes a lot, it may be worth configuring your CI to automatically re-run failing tests before reporting a failed build.

MouseEventFailed errors

When Poltergeist clicks on an element, rather than generating a DOM click event, it actually generates a "proper" click. This is much closer to what happens when a real user clicks on the page - but it means that Poltergeist must scroll the page to where the element is, and work out the correct co-ordinates to click. If the element is covered up by another element, the click will fail (this is a good thing - because your user won't be able to click a covered up element either).

Sometimes there can be issues with this behavior. If you have problems, it's worth taking screenshots of the page and trying to work out what's going on. If your click is failing, but you're not getting a MouseEventFailed error, then you can turn on the :debug option and look in the output to see what co-ordinates Poltergeist is using for the click. You can then cross-reference this with a screenshot to see if something is obviously wrong.

If you can't figure out what's going on and just want to work around the problem so you can get on with life, consider using a DOM click event. For example, if this code is failing:

click_button "Save"

Then try:


Timing problems

Sometimes tests pass and fail sporadically. This is often because there is some problem synchronising events properly. It's often straightforward to verify this by adding sleep statements into your test to allow sufficient time for the page to settle.

If you have these types of problems, read through the Capybara documentation on asynchronous JavaScript which explains the tools that Capybara provides for dealing with this.

Memory leak

If you run a few capybara sessions manually please make sure you've called session.driver.quit when you don't need session anymore. Forgetting about this causes memory leakage and your system's resources can be exhausted earlier than you may expect.

General troubleshooting hints

  • Configure Poltergeist with :debug turned on so you can see its communication with PhantomJS.
  • Take screenshots to figure out what the state of your page is when the problem occurs.
  • Use the remote web inspector in case it provides any useful insight
  • Consider downloading the Poltergeist source and using console.log debugging to figure out what's going on inside PhantomJS. (This will require an understanding of the Poltergeist source code and PhantomJS, so it's only for the committed!)

Filing a bug

If you can provide specific steps to reproduce your problem, or have specific information that might help other help you track down the problem, then please file a bug on Github.

Include as much information as possible. For example:

  • Specific steps to reproduce where possible (failing tests are even better)
  • The output obtained from running Poltergeist with :debug turned on
  • Screenshots
  • Stack traces if there are any Ruby on JavaScript exceptions generated
  • The Poltergeist and PhantomJS version numbers used
  • The operating system name and version used


Version history and a list of next-release features and fixes can be found in the changelog.


Copyright (c) 2011-2015 Jonathan Leighton

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.