Home > firefox, html, javascript, web > Scraping AJAX web pages (Part 1)

Scraping AJAX web pages (Part 1)

Don’t forget to check out the rest of the series too!


You want to download a web page whose source if full of AJAX calls. You want the result that is shown in your browser, i.e. you want the generated (post-AJAX) source.

Consider this simple page: test.html. If you open it in your browser, you’ll see the text “Hi Crowbar!”. However, if you download this page with wget for instance, in the source code you’ll see the text “Hi lame crawler”. Explanation: your browser downloads and then interprets the page. The executed JavaScript code updates the DOM of the page. A simple downloader like wget doesn’t interpret the source of a page just grabs it.

Solution #1

One way for getting the post-AJAX source of a web page is to use Crowbar. “Crowbar is a web scraping environment based on the use of a server-side headless mozilla-based browser. Its purpose is to allow running javascript scrapers against a DOM to automate web sites scraping…

When you launch Crowbar, it offers a RESTful web service listening by default on port 10000. Just open the page The trick behind Crowbar is that it turns a web browser into a web server.

Now we can download AJAX pages with wget the following way. Let’s get the previous test page:

wget "" -O tricky.html

If you check the source of the saved file, you will see the post-AJAX source that you would normally see in a web browser. You can also pass some other parameters to the Crowbar web service, they are detailed here. The most important parameter is “delay” that tells Crowbar how much it should wait after the page has terminated loading before attempting to serialize its DOM. By default its value is 3000 msec, i.e. 3 sec. If the page you want to download contains lots of AJAX calls then consider increasing the delay, otherwise you will get an HTML source that is not fully expanded yet.

Use case:
I wanted to download the following page from the NCBI database: CP002059.1. The page is quite big (about 5 MB), thus I had to wait about 10 sec. to get it in my browser. From the command-line I could fetch it this way (I gave it some extra time to be sure):

wget "" -O CP002059.1.html

Notes: If you want to download data from NCBI, there is a better way.

Did you know?
In Firefox, if you look at the source of a page (View -> Page Source), you will see the downloaded (pre-AJAX) source. If you want to see the generated (post-AJAX) source, you can use the Web Developer add-on (View Source -> View Generated Source).

Also, still in Firefox, if you save a web page with File -> Save Page As… and you choose “Web Page, HTML only”, Firefox will save the original (pre-AJAX) source. If you want the fully expanded (generated) source, choose the option “Web Page, complete”.

Solution #2
Another solution is to write a program/script that uses the webkit open source browser engine. In an upcoming post I will show you how to do it with Python.

Crowbar launch script for Linux:


# my crowbar is installed here: /opt/crowbar
# location of this file: /opt/crowbar/start.sh
xulrunner --install-app xulapp
xulrunner xulapp/application.ini

Crowbar launch script for Windows (update of 20110601):

rem My crowbar is installed here: c:\Program Files\crowbar
rem Location of this file: c:\Program Files\crowbar\start.bat

"%XULRUNNER_HOME%\xulrunner.exe" --install-app xulapp
"%XULRUNNER_HOME%\xulrunner.exe" xulapp\application.ini

XULRunner for Windows can be downloaded from here.

/ discussion /

  1. alex
    May 23, 2011 at 20:53


    I tried crowbar with the test page you provided. It works fine. However, I tried it with translate.google.com page for two languages and a simple word and it did not return rendered html file.

    Could you please let me know how it could be fixed.


  2. mark
    June 1, 2011 at 15:58

    Hi, thanks for the info on Crowbar. It is the most complete I’ve seen.

    I’m having a problem: When I navigate to page

    The browser displays:

    “” is not set up to establish an connection on port 10000 with this computer.

    When I use wget: wget “” -O CP002059

    The command line prompt displays:

    “Connection refused”

    Any help would be greatly appreciated.

    By the way, I am developing a scrapping application in VB.NET and I am using htmlagilitypack for parsing HTML tags.

    The big problem I’ve run into is that I am unable to figure out the font size of text when the font size is specified by CSS class. If the CSS style of an element is from an External Style Sheet it is potentially an even more difficult problem to solve.

    I was hoping that Crowbar could be used to get the computed CSS style of various html elements in pages that I scrape.

    Perhaps there is something very basic that I don’t understand about what Crowbar is useful for, and any guidance you can give would be greatly appreciated.


    • June 1, 2011 at 21:03

      Do you use Windows? I think that because of VB.NET… I tried this method under Linux, I don’t know if Crowbar works with Windows.

      Edit: sorry, I checked the Crowbar home page and they say it runs under Windows. I will try it and tell you how far I got.

      Edit #2: I could install Crowbar under Windows without any problem. (For checking out the Subversion repository, I used the svn command from the Cygwin environment). In the text of the post above I also added a launch script. When I launched it, Windows asked me if I want to allow or block it. “Allow” it. So your problem must be a firewall problem, Windows blocks the given port. Look around the settings of your Firewall how to allow the port 10000.

      After that how you extract the desired data from CSS, now it’s up to you :)

  3. June 14, 2011 at 08:33

    can a single instance of Crowbar fetch multiple web pages simultaneously ?
    Currently, for a java application, I am resorting to multithreading and using mutual exclusion by threads to fetch a page.
    Can this be done concurrently ?

  1. December 27, 2012 at 16:49
  2. August 7, 2014 at 04:40

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