About the data

Data Location

The Common Crawl dataset lives on Amazon S3 as part of the Amazon Public Datasets program. Downloading them is free from any instance on Amazon EC2, both via S3 and HTTP.

As the Common Crawl Foundation has evolved over the years, so has the format and metadata that accompany the crawls themselves.

[ARC] Archived Crawl #1 - s3://aws-publicdatasets/common-crawl/crawl-001/ - crawl data from 2008/2010
[ARC] Archived Crawl #2 - s3://aws-publicdatasets/common-crawl/crawl-002/ - crawl data from 2009/2010
[ARC] Archived Crawl #3 - s3://aws-publicdatasets/common-crawl/parse-output/ - crawl data from 2012
[WARC] s3://aws-publicdatasets/common-crawl/crawl-data/CC-MAIN-2013-20/
[WARC] s3://aws-publicdatasets/common-crawl/crawl-data/CC-MAIN-2013-48/
[WARC] s3://aws-publicdatasets/common-crawl/crawl-data/CC-MAIN-2014-10/
[WARC] s3://aws-publicdatasets/common-crawl/crawl-data/CC-MAIN-2014-15/

For all crawls since 2013, the crawls are stored in the WARC file format and also contain metadata and text data extracts. Starting since the 2014-15 crawl, we also provide file path lists for the segments, WARC, WAT, and WET files.

By replacing s3://aws-publicdatasets/ with https://aws-publicdatasets.s3.amazonaws.com/ on each line, you can obtain the HTTP path for any of the files stored on S3.

Data Format

Common Crawl currently stores the crawl data using the Web ARChive (WARC) format. Before that point, the crawl was stored in the ARC file format. The WARC format allows for more efficient storage and processing of Common Crawl's free multi-billion page web archives, which can be hundreds of terabytes in size. This document aims to give you an introduction to working with the new format, specifically the difference between:

WARC files which store the raw crawl data
WAT files which store computed metadata for the data stored in the WARC
WET files which store extracted plaintext from the data stored in the WARC

If you want all the nitty gritty details, the best source is the ISO standard, for which the final draft is available. If you're more interested in diving into code, we've provided three introductory examples in Java that use the Hadoop framework to process WAT, WET and WARC.

WARC Format

The WARC format is the raw data from the crawl, providing a direct mapping to the crawl process. Not only does the format store the HTTP response from the websites it contacts (WARC-Type: response), it also stores information about how that information was requested (WARC-Type: request) and metadata on the crawl process itself (WARC-Type: metadata).

For the HTTP responses themselves, the raw response is stored. This not only includes the response itself, what you would get if you downloaded the file, but also the HTTP header information, which can be used to glean a number of interesting insights. In the example below, we can see the crawler contacted http://102jamzorlando.cbslocal.com/tag/nba/page/2/ and received a HTML page in response. We can also see the page was served from the nginx web server and that a special header has been added, X-hacker, purely for the purposes of advertising to a very specific audience of programmers who might look at the HTTP headers!

WARC/1.0
WARC-Type: response
WARC-Date: 2013-12-04T16:47:32Z
WARC-Record-ID: 
Content-Length: 73873
Content-Type: application/http; msgtype=response
WARC-Warcinfo-ID: 
WARC-Concurrent-To: 
WARC-IP-Address: 23.0.160.82
WARC-Target-URI: http://102jamzorlando.cbslocal.com/tag/nba/page/2/
WARC-Payload-Digest: sha1:FXV2BZKHT6SQ4RZWNMIMP7KMFUNZMZFB
WARC-Block-Digest: sha1:GMYFZYSACNBEGHVP3YFQNOSTV5LPXNAU

HTTP/1.0 200 OK
Server: nginx
Content-Type: text/html; charset=UTF-8
Vary: Accept-Encoding
Vary: Cookie
X-hacker: If you're reading this, you should visit automattic.com/jobs and apply to join the fun, mention this header.
Content-Encoding: gzip
Date: Wed, 04 Dec 2013 16:47:32 GMT
Content-Length: 18953
Connection: close


...HTML Content...

WAT Response Format

WAT files contain important metadata about the records stored in the WARC format above. This metadata is computed for each of the three types of records (metadata, request, and response). If the information crawled is HTML, the computed metadata includes the HTTP headers returned and the links (including the type of link) listed on the page.

This information is stored as JSON. To keep the file sizes as small as possible, the JSON is stored with all unnecessary whitespace stripped, resulting in a relatively unreadable format for humans. If you want to inspect the JSON file yourself, use one of the many JSON pretty print tools available.

The HTTP response metadata is most likely to be of interest to Common Crawl users. The skeleton of the JSON format is outlined below.

WARC-Header-Metadata
Payload-Metadata
- HTTP-Response-Metadata
  - Headers
    - HTML-Metadata
      - Head
        
        Title
        
        Scripts
        
        Metas
        
        Links
      - Links
Container

WET Response Format

As many tasks only require textual information, the Common Crawl dataset provides WET files that only contain extracted plaintext. The way in which this textual data is stored in the WET format is quite simple. The WARC metadata contains various details, including the URL and the length of the plaintext data, with the plaintext data following immediately afterwards.

WARC/1.0
WARC-Type: conversion
WARC-Target-URI: http://advocatehealth.com/condell/emergencyservices3
WARC-Date: 2013-12-04T15:30:35Z
WARC-Record-ID: 
WARC-Refers-To: 
WARC-Block-Digest: sha1:3SJBHMFPOCUJEHJ7OMGVCRSHQTWLJUUS
Content-Type: text/plain
Content-Length: 5765


...Text Content...

Processing the file format

We've provided three introductory examples in Java for the Hadoop framework. The code also contains wrapper tools for making working with the Web Archive Commons library easier in Hadoop. These introductory examples include:

Count the number of times varioustags are used across HTML on the internet using the WARC files
Counting the number of different server types found in the HTTP headers using the WAT files
Word count over the extracted plaintext found in the WET files

If you're using a different language, there are a number of open source libraries that handle processing these WARC files and the content they contain. These include:

Common Crawl's Example WARC (Java & Clojure)
WARC-Mapreduce WET/WARC processor (Java & Clojure)
Kevin Bullaughey's WARC & WAT tools (Go)
Hanzo Archive's Warc Tools (Python)
IIPC's Web Archive Commons library for processing WARC & WAT (Java)
Internet Archive’s Hadoop tools for bridging WARC to Pig (Java)

If in doubt, the tools provided as part of the IIPC's Web Archive Commons library are the preferred implementation.

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