Use Capybara to drive Chrome in headless mode via the debugging protocol.


Add this line to your application's Gemfile:

gem 'capybara-chrome'

And then execute:

$ bundle

Or install it yourself as:

$ gem install capybara-chrome

Using Docker

Add this line to your Dockerfile to install Chrome:

  RUN curl -sL -o chrome-stable.deb ; dpkg -i chrome-stable.deb ; apt-get install -fy; rm -rf /var/lib/apt/lists/*

In my experience, headless Chrome cannot be run as root, so you need to run rspec as an unprivileged user and use this flag with docker run

docker run --security-opt seccomp=unconfined


Capybara.javascript_driver = :chrome
Capybara::Chrome.configuration.chrome_port = 9222 # optional

The standard port for the debugging protocol is 9222. Visit localhost:9222 in a Chrome tab to watch the tests execute. Note, the port will be random by default.

Using thin

I like using thin instead of WEBrick as my Capybara server. It's a little faster, gives me greater control of logging, shows errors, and allows me to disable signal handlers. Below are my settings:

Capybara.register_server :thin do |app, port, host|
  require "rack/handler/thin"
  Thin::Logging.silent = false
  # Thin::Logging.debug = true # uncomment to see request and response codes
  # Thin::Logging.trace = true # uncomment to see full requests/responses, Host: host, Port: port, signals: false)
Capybara.server = :thin


Use byebug instead of binding.pry when debugging a test. The Pry debugger tends to hang when visit is called.

Using the repl

You can use the capybara-chrome browser without providing a rack app. This can be helpful in debugging.

[2] pry(main)> driver =, port:9222); driver.start; browser = driver.browser
[3] pry(main)> browser.visit ""
=> true
[4] pry(main)> browser.current_url
=> ""
[5] pry(main)>

Further, you can run a local netcat server and point the capybara-chrome browser to it to see the entire request that's being sent.

Terminal one contains the browser:

[1] pry(main)> driver =, port:9222); driver.start; browser = driver.browser
[2] pry(main)> browser.header "x-foo", "bar"
[3] pry(main)> browser.visit "http://localhost:8000"

Terminal two prints the request

$ while true; do { echo -e "HTTP/1.1 200 OK \r\n"; echo "hi"; } | nc -l 8000; done
GET / HTTP/1.1
Host: localhost:8000
Connection: keep-alive
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) HeadlessChrome/68.0.3440.106 Safari/537.36
x-foo: bar
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8
Accept-Encoding: gzip, deflate


A video showing capybara-chrome running in a browser tab

Preview of visualizing capybara-chrome

A video demonstrating debugging an rspec test with byebug

Preview of debugging capybara-chrome

A video showing capybara-chrome running against a netcat backend

Preview of debugging capybara-chrome with netcat


Bug reports and pull requests are welcome on GitHub at


The gem is available as open source under the terms of the MIT License.