Open Directory Project

Open Directory Project
Open Directory Project
Commercial? No
Type of site Web directory
Registration Optional
Content license Creative Commons Attribution 3.0 Unported
Owner Netscape (AOL)
Created by Netscape
Launched June 5, 1998
Alexa rank decrease 639 (November 2011)[1]

The Open Directory Project (ODP), also known as Dmoz (from, its original domain name), is a multilingual open content directory of World Wide Web links. It is owned by Netscape but it is constructed and maintained by a community of volunteer editors.

ODP uses a hierarchical ontology scheme for organizing site listings. Listings on a similar topic are grouped into categories which can then include smaller categories.


Project information

ODP was founded in the United States as Gnuhoo by Rich Skrenta and Bob Truel in 1998 while they were both working as engineers for Sun Microsystems. Chris Tolles, who worked at Sun Microsystems as the head of marketing for network security products, also signed on in 1998 as a co-founder of Gnuhoo along with co-founders Bryn Dole and Jeremy Wenokur. Skrenta had developed TASS, an ancestor of tin, the popular threaded Usenet newsreader for Unix systems. Coincidentally, the original category structure of the Gnuhoo directory was based loosely on the structure of Usenet newsgroups then in existence.

The Gnuhoo directory went live on June 5, 1998. After a Slashdot article suggested that Gnuhoo had nothing in common with the spirit of free software,[2] for which the GNU project was known, Richard Stallman and the Free Software Foundation objected to the use of Gnu. So Gnuhoo was changed to NewHoo. Yahoo! then objected to the use of "Hoo" in the name, prompting them to switch the name again. ZURL was the likely choice.[3] However, before the switch to ZURL, NewHoo was acquired by Netscape Communications Corporation in October 1998 and became the Open Directory Project. Netscape released the ODP data under the Open Directory License. Netscape was acquired by AOL shortly thereafter and ODP was one of the assets included in the acquisition. AOL later merged with Time-Warner.

ODP size by date.

By the time Netscape assumed stewardship, the Open Directory Project had about 100,000 URLs indexed with contributions from about 4500 editors. On October 5, 1999, the number of URLs indexed by ODP reached one million. According to an unofficial estimate, the URLs in the Open Directory numbered 1.6 million in April 2000, surpassing those in the Yahoo! Directory.[4] ODP achieved the milestones of indexing two million URLs on August 14, 2000, three million listings on November 18, 2001 and four million on December 3, 2003.

From January 2006 the Open Directory published online reports to inform the public about the development of the project. The first report covered the year 2005. Monthly reports were issued subsequently until September 2006.[5] These reports gave greater insight into the functioning of the directory than the simplified statistics given on the front page of the directory. The number of listings and categories cited on the front page include "Test" and "Bookmarks" categories but these are not included in the RDF dump offered to users. The total number of editors who have contributed to the directory as of March 31, 2007 was 75,151.[6] There were about 7330 active editors during August 2006.[5]

System failure and editing outage, October to December 2006

On October 20, 2006, the ODP's main server suffered a catastrophic failure of the system[7] that prevented editors from working on the directory until December 18, 2006. During that period, an older build of the directory was visible to the public. On January 13, 2007, the Site Suggestion and Update Listings forms were again made available.[8] On January 26, 2007, weekly publication of RDF dumps resumed. To avoid future outages, the system now resides on a redundant configuration of two Intel-based servers.[9]

Competing and spinoff projects

As the ODP became more widely known, two other major web directories edited by volunteers and sponsored by and Zeal emerged, both now defunct. These directories did not license their content for open content distribution.[10][11]

The concept of using a large-scale community of editors to compile online content has been successfully applied to other types of projects. ODP's editing model directly inspired three other open content volunteer projects: an open content restaurant directory known as ChefMoz,[12] an open content music directory known as MusicMoz,[13] and an encyclopedia known as Open Site.[14]


Open Directory Project front page, January 2006

Gnuhoo borrowed the basic outline for its initial ontology from Usenet. In 1998, Rich Skrenta said, "I took a long list of groups and hand-edited them into a hierarchy."[15] For example, the topic covered by the newsgroup was represented by the category Computers/AI/Artificial_Life. The original divisions were for Adult, Arts, Business, Computers, Games, Health, Home, News, Recreation, Reference, Regional, Science, Shopping, Society and Sports. While these fifteen top-level categories have remained intact, the ontology of second- and lower-level categories has undergone a gradual evolution; significant changes are initiated by discussion among editors and then implemented when consensus has been reached.

In July 1998, the directory became multilingual with the addition of the World top-level category. The remainder of the directory lists only English language sites. By May 2005, seventy-five languages were represented. The growth rate of the non-English components of the directory has been greater than the English component since 2002. While the English component of the directory held almost 75% of the sites in 2003, the World level grew to over 1.5 million sites as of May 2005, forming roughly one-third of the directory. The ontology in non-English categories generally mirrors that of the English directory, although exceptions which reflect language differences are quite common.

Several of the top-level categories have unique characteristics. The Adult category is not present on the directory homepage but it is fully available in the RDF dump that ODP provides. While the bulk of the directory is categorized primarily by topic, the Regional category is categorized primarily by region. This has led many to view ODP as two parallel directories: Regional and Topical.

On November 14, 2000, a special directory within the Open Directory was created for people under 18 years of age.[16] Key factors distinguishing this "Kids and Teens" area from the main directory are:

  • stricter guidelines which limit the listing of sites to those which are targeted or "appropriate" for people under 18 years of age;[17]
  • category names as well as site descriptions use vocabulary which is "age appropriate";
  • age tags on each listing distinguish content appropriate for kids (age 12 and under), teens (13 to 15 years old) and mature teens (16 to 18 years old);
  • Kids and Teens content is available as a separate RDF dump;
  • editing permissions are such that the community is parallel to that of the Open Directory.

By May 2005, this portion of the Open Directory included over 32,000 site listings.

Since early 2004, the whole site has been in UTF-8 encoding. Prior to this, the encoding used to be ISO 8859-1 for English language categories and a language-dependent character set for other languages. The RDF dumps have been encoded in UTF-8 since early 2000.


Directory listings are maintained by editors. While some editors focus on the addition of new listings, others focus on maintaining the existing listings. This includes tasks such as the editing of individual listings to correct spelling and/or grammatical errors, as well as monitoring the status of linked sites. Still others go through site submissions to remove spam and duplicate submissions.

Robozilla is a Web crawler written to check the status of all sites listed in ODP. Periodically, Robozilla will flag sites which appear to have moved or disappeared and editors follow up to check the sites and take action. This process is critical for the directory in striving to achieve one of its founding goals: to reduce the link rot in web directories. Shortly after each run, the sites marked with errors are automatically moved to the unreviewed queue where editors may investigate them when time permits.

Due to the popularity of the Open Directory and its resulting impact on search engine rankings (See PageRank), domains with lapsed registration that are listed on ODP have attracted domain hijacking, an issue that has been addressed by regularly removing expired domains from the directory.

While corporate funding and staff for the ODP have diminished in recent years, volunteers have created editing tools such as linkcheckers to supplement Robozilla, category crawlers, spellcheckers, search tools that directly sift a recent RDF dump, bookmarklets to help automate some editing functions, mozilla based add-ons,[18] and tools to help work through unreviewed queues.

License and requirements

ODP data is made available for open content distribution under the terms of the Open Directory License, which requires a specific ODP attribution table on every Web page that uses the data.

The Open Directory License also includes a requirement that users of the data continually check the ODP site for updates and discontinue use and distribution of the data or works derived from the data once an update occurs. This restriction prompted the Free Software Foundation to refer to the Open Directory License as a non-free documentation license, citing the right to redistribute a given version not being permanent and the requirement to check for changes to the license.[19]

RDF dumps

ODP data is made available through an RDF-like dump that is published on a dedicated download server, where an archive of previous versions is also available.[20] New versions are usually generated weekly. An ODP editor has catalogued a number of bugs that are/were encountered when implementing the ODP RDF dump, including UTF-8 encoding errors (fixed since August 2004) and an RDF format that does not comply with the final RDF specification because ODP RDF generation was implemented before the RDF specification was finalized.[21] So while today the so-called RDF dump is valid XML, it is not strictly RDF but an ODP-specific format and as such, software to process the ODP RDF dump needs to take account of this.

Content users

ODP data powers the core directory services for many of the Web's largest search engines and portals, including Netscape Search, AOL Search, and Alexa. Google Directory used ODP information, until being shuttered in July 2011.[22]

Other uses are also made of ODP data. For example, in the spring of 2004 Overture announced a search service for third parties combining Yahoo! Directory search results with ODP titles, descriptions and category metadata. The search engine Gigablast announced on May 12, 2005 its searchable copy of the Open Directory. The technology permits search of websites listed in specific categories, "in effect, instantly creating over 500,000 vertical search engines".[23]

As of 8 September 2006 (2006 -09-08), the ODP listed 313 English-language Web sites that use ODP data as well as 238 sites in other languages.[24] However, these figures do not reflect the full picture of use, as those sites that use ODP data without following the terms of the ODP license are not listed.

Policies and procedures

There are restrictions imposed on who can become an ODP editor. The primary gatekeeping mechanism is an editor application process wherein editor candidates demonstrate their editing abilities, disclose affiliations that might pose a conflict of interest and otherwise give a sense of how the applicant would likely mesh with the ODP culture and mission.[25] A majority of applications are rejected but reapplying is allowed and sometimes encouraged. The same standards apply to editors of all categories and subcategories.

ODP's editing model is a hierarchical one. Upon becoming editors, individuals will generally have editing permissions in only a small category. Once they have demonstrated basic editing skills in compliance with the Editing Guidelines, they are welcome to apply for additional editing privileges in either a broader category or in a category elsewhere in the directory. Mentorship relationships between editors are encouraged and internal forums provide a vehicle for new editors to ask questions.

ODP has its own internal forums, the contents of which are intended only for editors to communicate with each other primarily about editing topics. Access to the forums requires an editor account and editors are expected to keep the contents of these forums private.[26]

Over time, senior editors may be granted additional privileges which reflect their editing experience and leadership within the editing community. The most straightforward are editall privileges which allow an editor to access all categories in the directory. Meta privileges additionally allow editors to perform tasks such as reviewing editor applications, setting category features and handling external and internal abuse reports. Cateditall privileges are similar to editall but only for a single directory category. Similarly, catmod privileges are similar to meta but only for a single directory category. Catmv privileges allow editors to make changes to directory ontology by moving or renaming categories. All of these privileges are granted by admins and staff, usually after discussion with meta editors.

In August 2004, a new level of privileges called admin was introduced. Administrator status was granted to a number of long serving metas by staff. Administrators have the ability to grant editall+ privileges to other editors and to approve new directory-wide policies, powers which had previously only been available to root (staff) editors.[27] A full list of senior editors is available to the public,[28] as is a listing of all current editors.[29]

All ODP editors are expected to abide by ODP's Editing Guidelines. These guidelines describe editing basics: which types of sites may be listed and which may not; how site listings should be titled and described in a loosely consistent manner; conventions for the naming and building of categories; conflict of interest limitations on the editing of sites which the editor may own or otherwise be affiliated with; and a code of conduct within the community.[30] Editors who are found to have violated these guidelines may be contacted by staff or senior editors, have their editing permissions cut back or lose their editing privileges entirely. ODP Guidelines are periodically revised after discussion in editor forums.

Site submissions

One of the original motivations for forming Gnuhoo/Newhoo/ODP was the frustration that many people experienced in getting their sites listed on Yahoo! Directory. However Yahoo! has since implemented a paid service for timely consideration of site submissions. That lead has been followed by many other directories. Some accept no free submissions at all. By contrast the ODP has maintained its policy of free site submissions for all types of site—the only one of the major general directories to do so.

One result has been a gradual divergence between the ODP and other directories in the balance of content. The pay-for-inclusion model favours those able and willing to pay, so commercial sites tend to predominate in directories using it.[31] Conversely, a directory manned by volunteers will reflect the aims and interests of those volunteers. The ODP lists a high proportion of informational and non-profit sites.

Another consequence of the free submission policy is that the ODP has enormous numbers of submissions still waiting for review. In large parts those consist of spam and incorrectly submitted sites.[32] So the average processing time for a site submission has grown longer with each passing year. However the time taken cannot be predicted, since the variation is so great: a submission might be processed within hours or take several years.[33] However, site suggestions are just one of many sources of new listings. Editors are under no obligation to check them for new listings and are actually encouraged to use other sources.[33][34]

Controversy and criticism

There have long been allegations that volunteer ODP editors give favorable treatment to their own websites while concomitantly thwarting the good faith efforts of their competition.[35] Such allegations are fielded by ODP's staff and meta editors, who have the authority to take disciplinary action against volunteer editors who are suspected of engaging in abusive editing practices.[36] In 2003, ODP introduced a new Public Abuse Report System that allows members of the general public to report and track allegations of abusive editor conduct using an online form.[37] Uninhibited discussion of ODP's purported shortcomings has become more common on mainstream Webmaster discussion forums. Although site policies suggest that an individual site should be submitted to only one category,[38] as of October 2007,, a news aggregation site operated by ODP founder Rich Skrenta, has more than 10,000 listings.[39]

Early in the history of the ODP, its staff gave representatives of selected companies, such as Rolling Stone or CNN, editing access in order to list individual pages from their websites.[40] Links to individual CNN articles have been added until 2004 and have been entirely removed from the directory in January 2008[41] due to being outdated and not considered worth the effort to maintain. Such experiments have not been repeated later.

Ownership and management

Underlying some controversy surrounding ODP is its ownership and management. Some of the original GnuHoo volunteers felt that they had been deceived into joining a commercial enterprise.[2] To varying degrees, those complaints have continued up until the present.

At ODP's inception, there was little thought given to the idea of how ODP should be managed and there were no official forums, guidelines or FAQs. In essence, ODP began as a free for all.[42]

As time went on, the ODP Editor Forums became the de facto ODP parliament and when one of ODP's staff members would post an opinion in the forums, it would be considered an official ruling.[26] Even so, ODP staff began to give trusted senior editors additional editing privileges, including the ability to approve new editor applications, which eventually led to a stratified hierarchy of duties and privileges among ODP editors, with ODP's paid staff having the final say regarding ODP's policies and procedures.[27][43]

Editor removal procedures

ODP's editor removal procedures are overseen by ODP's staff and meta editors. According to ODP's official editorial guidelines, editors are removed for abusive editing practices or uncivil behaviour. Discussions that may result in disciplinary action against volunteer editors take place in a private forum which can only be accessed by ODP's staff, meta editors and volunteer editors who are being discussed are not given notice that such proceedings are taking place.[43] Some people find this arrangement distasteful, wanting instead a discussion modelled more like a trial held in the U.S. judicial system.[44]

In the article Editor Removal Explained, ODP meta editor Arlarson states that "a great deal of confusion about the removal of editors from ODP results from false or misleading statements by former editors".[45]

The ODP's confidentiality guidelines prohibit any current ODP editors in a position to know anything from discussing the reasons for specific editor removals.[43] However, a generic list of reasons is for example given in the guidelines.[46] In the past, this has led to removed ODP editors wondering why they cannot login at ODP to perform their editing work.[47][48]

Allegations that editors are removed for criticizing policies

David F. Prenatt, Jr. (former ODP editor netesq) and the former editor known by the alias The Cunctator claim to have been removed for disagreeing with staff about changes to the policies, with special regard to the ODP's copyright policies. According to their claims, staff used the excuse that their behaviour was uncivil to remove bothersome editors.[44][49][50]

Blacklisting allegations

Senior ODP editors have the ability to attach "warning" or "do not list" notes to individual domains but no editor has the unilateral ability to block certain sites from being listed. Sites with these notes might still be listed and at times notes are removed after some discussion.[51]

Hierarchical structure

Recently criticism of ODP's hierarchical structure emerged. Many believe hierarchical directories are too complicated. As the recent emergence of Web 2.0, folksonomies began to appear. These people thought folksonomies, networks and directed graph are more "natural" and easier to manage than hierarchies.[52][53][54]



The ODPSearch software is a derivative version of Isearch which is open source, licensed under the Mozilla Public License.[55]

Editor forums

The ODP Editor Forums were originally run on software that was based on the proprietary Ultimate Bulletin Board system. In June 2003, they switched to the open source phpBB system. As of 2007, these forums are powered by a modified version of phpBB.

Bug tracking

The bug tracking software used by the ODP is Bugzilla and the web server Apache. Squid web proxy server was also used but it was removed in August 2007 when the storage servers were reorganized. All these applications are open source.


The ODP database/editing software is closed source (although Richard Skrenta of ODP did say in June 1998 that he was considering licensing it under the GNU General Public License). This has led to criticism from the aforementioned GNU project, many of whom also criticise the ODP content license.[56]

As such, there have been some efforts to provide alternatives to ODP. These alternatives would allow communities of like-minded editors to set up and maintain their own open source/open content Web directories. However, no significant open source/open content alternative to ODP has emerged.

See also


  1. ^ " Site Info". Alexa Internet. Retrieved 2011-11-02. 
  2. ^ a b "The GnuHoo BooBoo". Slashdot. Retrieved April 27, 2007. 
  3. ^ Zurl Directory, archived version of blog entry dated May 29, 2004 by Skrenta, founder of the ODP.
  4. ^ ODP and Yahoo Size Charts by ODP editor geniac
  5. ^ a b ODP reports by ODP volunteer administrator chris2001
  6. ^ ODP Front Page, retrieved August 15, 2006
  7. ^ "Dmoz's Catastrophic Server/Hardware Failure" October 27, 2006, retrieved November 15, 2006.
  8. ^ technical problems at (retrieved January 13, 2007).
  9. ^ The Hamsters' New Home, in: Open Directory newsletter issue Winter 2006, retrieved December 26, 2006.
  10. ^ Zeal Terms of use taken from
  11. ^ GO Network Terms of Service and Conditions of use taken from
  12. ^ ChefMoz Fine Dining Menu, in: Open Directory newsletter issue Autumn 2003
  13. ^ About MusicMoz, on
  14. ^ help on
  15. ^ Danny Sullivan, NewHoo: Yahoo Built By The Masses, Search Engine Watch, July 1, 1998
  16. ^ Kids and Teens Launches! Open Directory Project Newsletter, November/December 2000
  17. ^ Kids&Teens Guidelines
  18. ^ "ODPExtension" Mozilla based add-on, ODP Magic.. formerly known as ODP Extension
  19. ^ Gnu Project: Non-Free Documentation Licenses
  20. ^ Open Directory RDF Dump
  21. ^ ODP/dmoz Data Dump ToDo List
  22. ^ "Google Streamlining: Say Goodbye to the Google Directory and Labs!". Pandia Search Engine News. 21 July 2011. Retrieved 25 July 2011. 
  23. ^ 500,000 Vertical Search Engines, a press release from May 12, 2005
  24. ^ Category: Sites Using ODP Data on Retrieved on September 8, 2006.
  25. ^ Become an Editor at the Open Directory Project
  26. ^ a b ODP Communication Guidelines
  27. ^ a b Open Directory Project Administrator Guidelines
  28. ^ Open Directory Meta-editor report
  29. ^ Open Directory Editor list
  30. ^ ODP Directory Editorial Guidelines
  31. ^ When Giant Directories Roamed the Earth, an example showing the initial impact on Looksmart.
  32. ^ RZ-Posting by Meta-Editor hutcheson
  33. ^ a b FAQ: How long until my site will be reviewed? on
  34. ^ ODP Help Resources in the official DMOZ Blog on 21.01.2009
  35. ^ How To: ODP Editor Is Competitor posted on in 2000
  36. ^ ODP Meta Guidelines: Editor Abuse and Removal, accessed October 9, 2008.
  37. ^ Open Directory Project: Public Abuse Report System.
  38. ^ How to suggest a site to the Open Directory
  39. ^ Open Directory Project Search: "topix" (accessed October 18, 2007)
  40. ^ Multiple URL's in DMOZ posted on in 2003
  41. ^, taken from
  42. ^ Laisha, The History of the Open Directory Project in Search Engine Laisha's List, June, 1999.
  43. ^ a b c Open Directory Project Meta Guidelines
  44. ^ a b XODP Yahoo! Group Message Archive
  45. ^ Arlarson, Editor Removal Explained, Open Directory Project Newsletter (September 2000).
  46. ^ Guidelines: Account Removal
  47. ^ Thread: Editor account expired on Resource-Zone
  48. ^ Thread: Can't Login on Resource-Zone
  49. ^ David F. Prenatt, Jr., Life After the Open Directory Project, (June 1, 2000).
  50. ^ CmdrTaco (October 24, 2000). "Dmoz (aka AOL) Changing Guidelines In Sketchy Way". Slashdot. 
  51. ^ Add Note to URL Feature, in ODP Documentation
  52. ^ Hriţcu, C., (April 8, 2005). "Folksonomies vs. Ontologies". 
  53. ^ Shirky, C. (March 15, 2005). "Ontology is Overrated: Links, Tags and Post-hoc Metadata". ITConversations. 
  54. ^ Hammond, T.; Hannay, T.; Lund, B. & Scott, J. (April 2005). "Social Bookmarking Tools (I)". D-Lib Magazine. 
  55. ^ Open Directory Search Guide
  56. ^ FSF: Non-Free Documentation Licenses: "The primary problems are that your right to redistribute any given version is not permanent and that it requires the user to keep checking back at that site, which is too restrictive of the user's freedom."

External links

Wikimedia Foundation. 2010.

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