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Transform HTML into PDF/PNG/JPEG using Google Puppeteer/Chromium
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A Ruby gem to transform HTML into PDFs, PNGs or JPEGs using Google Puppeteer and Chromium.



Add this line to your application's Gemfile:

gem 'grover'

Google Puppeteer

npm install puppeteer


# accepts a URL or inline HTML and optional parameters for Puppeteer
grover ='', format: 'A4')

# Get an inline PDF
pdf = grover.to_pdf

# Get a screenshot
png = grover.to_png
jpeg = grover.to_jpeg 

# Options can be provided through meta tags'<html><head><meta name="grover-page_ranges" content="1-3"')'<html><head><meta name="grover-margin-top" content="10px"')


  • options are underscore case, and sub-options separated with a dash
  • all options can be overwritten, including emulate_media and display_url

From a view template

It's easy to render a normal Rails view template as a PDF, using Rails' render_to_string:

html ={
  template: 'controller/view',
  layout: 'my_layout',
  locals: { :@instance_var => ... }
pdf =, grover_options).to_pdf

Relative paths

If calling Grover directly (not through middleware) you will need to either specify a display_url or modify your HTML by converting any relative paths to absolute paths before passing to Grover.

This can be achieved using the HTML pre-processor helper:

absolute_html = Grover::HTMLPreprocessor.process relative_html, 'http://my.server/', 'http'

This is important because Chromium will try and resolve any relative paths via the display url host. If not provided, the display URL defaults to

Why would you pre-process the HTML rather than just use the display_url

There are many scenarios where specifying a different host of relative paths would be preferred. For example, your server might be behind a NAT gateway and the display URL in front of it. The display URL might be shown in the header/footer, and as such shouldn't expose details of your private network.

If you run into trouble, take a look at the debugging section below which would allow you to inspect the page content and devtools.


Grover can be configured to adjust the layout of the resulting PDF/image.

For available PDF options, see

Also available are the emulate_media, cache, viewport, timeout and launch_args options.

# config/initializers/grover.rb
Grover.configure do |config|
  config.options = {
    format: 'A4',
    margin: {
      top: '5px',
      bottom: '10cm'
    viewport: {
      width: 640,
      height: 480
    prefer_css_page_size: true,
    emulate_media: 'screen',
    cache: false,
    timeout: 0, # Timeout in ms. A value of `0` means 'no timeout'
    launch_args: ['--font-render-hinting=medium'],
    wait_until: 'domcontentloaded' 

For available PNG/JPEG options, see

Note that by default the full_page option is set to false and you will get a 800x600 image. You can either specify the image size using the clip options, or capture the entire page with full_page set to true.

For viewport options, see

For launch_args options, see Launch parameter args can also be provided using a meta tag:

<meta name="grover-launch_args" content="['--disable-speech-api']" />

For wait_until option, default for URLs is networkidle2 and for HTML content networkidle0. For available options see

The wait_for_selector option can also be used to wait until an element appears on the page. Additional waiting parameters can be set with the wait_for_selector_options options hash. For available options, see:

The Chrome/Chromium executable path can be overridden with the executable_path option.

Javascript can be executed on the page (after render and before conversion to PDF/image) with the execute_script option.

Basic authentication

For requesting a page with basic authentication, username and password options can be provided. Note that this only really makes sense if you're calling Grover directly (and not via middleware).'<some URI with basic authentication', username: 'the username', password: 'super secret').to_pdf

Adding cookies

To set request cookies when requesting a URL, pass an array of hashes as such N.B. Only the name and value properties are required. See page.setCookies documentation for more details.

myCookies = [
  { name: 'sign_username', value: '', domain: 'mydomain' },
  { name: '_session_id', value: '9c014df0b699d8dc08d1c472f8cc594c', domain: 'mydomain' }
]'<some URI with cookies', cookies: myCookies).to_pdf

If you need to forward the cookies from the original request, you could extract them as such:

def header_cookies
  request.headers['Cookie'].split('; ').map do |cookie|
    key, value = cookie.split '='
    { name: key, value: value, domain: request.headers['Host'] }

And give that array to Grover:'<some URI with cookies', cookies: header_cookies).to_pdf

Page URL for middleware requests (or passing through raw HTML)

If you want to have the header or footer display the page URL, Grover requires that this is passed through via the display_url option. This is because the page URL is not available in the raw HTML!

For Rack middleware conversions, the original request URL (without the .pdf extension) will be passed through and assigned to display_url for you. You can of course override this by using a meta tag in the downstream HTML response.

For raw HTML conversions, if the display_url is not provided will be used as the default.

Header and footer templates

Should be valid HTML markup with following classes used to inject printing values into them:

  • date formatted print date
  • title document title
  • url document location
  • pageNumber current page number
  • totalPages total pages in the document


Grover comes with a middleware that allows users to get a PDF, PNG or JPEG view of any page on your site by appending .pdf, .png or .jpeg/.jpg to the URL.

Middleware Setup

Non-Rails Rack apps

# in
require 'grover'
use Grover::Middleware

Rails apps

# in application.rb
require 'grover'
config.middleware.use Grover::Middleware

N.B. by default PNG and JPEG are not modified in the middleware to prevent breaking standard behaviours. To enable them, there are configuration options for each image type as well as an option to disable the PDF middleware (on by default).

If either of the image handling middleware options are enabled, the ignore_path should also be configured, otherwise assets are likely to be handled which would likely result in 404 responses.

# config/initializers/grover.rb
Grover.configure do |config|
  config.use_png_middleware = true
  config.use_jpeg_middleware = true
  config.use_pdf_middleware = false


The root_url option can be specified either when configuring the middleware or as a global option. This is needed when running the Grover middleware behind a URL rewriting proxy or within a containerised system.

As a middleware option:

# in application.rb
require 'grover'
config.middleware.use Grover::Middleware, root_url: 'https://my.external.domain'

or as a global option:

# config/initializers/grover.rb
Grover.configure do |config|
  config.root_url = 'https://my.external.domain'


The ignore_path configuration option can be used to tell Grover's middleware whether it should handle/modify the response. There are three ways to set up the ignore_path:

  • a String which matches the start of the request path.
  • a Regexp which could match any part of the request path.
  • a Proc which accepts the request path as a parameter.
# config/initializers/grover.rb
Grover.configure do |config|
  # assigning a String
  config.ignore_path = '/assets/'
  # matches `` and not ``

  # assigning a Regexp
  config.ignore_path = /my\/path/
  # matches `` 

  # assigning a Proc
  config.ignore_path = ->(path) do
    /\A\/foo\/.+\/[0-9]+\.png\z/.match path 
  # matches ``

Cover pages

Since the header/footer for Puppeteer is configured globally, displaying of front/back cover pages (with potentially different headers/footers etc) is not possible.

To get around this, Grover's middleware allows you to specify relative paths for the cover page contents. For direct execution, you can make multiple calls and combine the resulting PDFs together.

Using middleware

You can specify relative paths to the cover page contents using the front_cover_path and back_cover_path options either via the global configuration, or via meta tags. These paths (with query parameters) are then requested from the downstream app.

The cover pages are converted to PDF in isolation, and then combined together with the original PDF response, before being returned back up through the Rack stack.

N.B To simplify things, the same request method and body are used for the cover page requests.

# config/initializers/grover.rb
Grover.configure do |config|
  config.options = {
    front_cover_path: '/some/global/cover/page?foo=bar'

Or via the meta tags in the original response:

    <meta name="grover-back_cover_path" content="/back/cover/page?bar=baz" />

Direct execution

To add a cover page using direct execution, you can make multiple calls and combine the results using the combine_pdf gem.

require 'combine_pdf'

  # ...

  def invoke(file_path)
    pdf = CombinePDF.parse(
    pdf >> CombinePDF.parse(
    pdf << CombinePDF.parse( file_path

Running on Heroku

To run Grover (Puppeteer) on Heroku follow these steps:

  1. Add the node buildpack. Puppeteer requires a node environment to run.

    heroku buildpacks:add heroku/nodejs --index=1 [--remote yourappname]
  2. Add the puppeteer buildpack. Make sure the puppeteer buildpack runs after the node buildpack and before the main ruby buildpack.

    heroku buildpacks:add jontewks/puppeteer --index=2 [--remote yourappname]
  3. Next, tell Grover to run Puppeteer in the "no-sandbox" mode by setting an ENV variable GROVER_NO_SANDBOX=true on your app dyno. Make sure that you trust all the HTML/JS you provide to Grover.

    heroku config:set GROVER_NO_SANDBOX=true [--remote yourappname]


If you're having trouble with converting the HTML content, you can enable some debugging options to help. These can be enabled as global options via Grover.configure, by passing through to the Grover initializer, or using meta tag options.

debug: {
  headless: false,  # Default true. When set to false, the Chromium browser will be displayed
  devtools: true    # Default false. When set to true, the browser devtools will be displayed.


  • The headless option disabled is not compatible with exporting of the PDF.
  • If showing the devtools, the browser will halt resulting in a navigation timeout


Bug reports and pull requests are welcome on GitHub at

Note that spec tests are appreciated to minimise regressions. Before submitting a PR, please ensure that:

$ rspec


$ rubocop

both succeed

Special mention

Thanks are given to the great work done in the PDFKit project. The middleware and HTML preprocessing components were used heavily in the implementation of Grover.

Thanks are also given to the excellent Schmooze project. The Ruby to NodeJS interface in Grover is heavily based off that work. Grover previously used that gem, however migrated away due to differing requirements over persistence/cleanup of the NodeJS worker process.


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