Company:Stack Exchange

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Short description: Network of Q&A sites based in New York City
Stack Exchange Network
Stack Exchange logo and wordmark.svg
Type of site
HeadquartersNew York City , New York, U.S.
OwnerStack Exchange Inc.[1]
Created by
  • Jeff Atwood
  • Joel Spolsky
LaunchedSeptember 2009; 14 years ago (2009-09)[2]
(relaunched in January 2011)[3]
Content license
User contributions under CC BY-SA 2.5, 3.0, and 4.0[4][5]

Stack Exchange is a network of question-and-answer (Q&A) websites on topics in diverse fields, each site covering a specific topic, where questions, answers, and users are subject to a reputation award process. The reputation system allows the sites to be self-moderating.[6] As of March 2023, the three most actively-viewed sites in the network are Stack Overflow (which focuses on computer programming), Unix & Linux, and Mathematics.[7]

All sites in the network are modeled after the initial site Stack Overflow which was created by Jeff Atwood and Joel Spolsky in 2008. Further Q&A sites in the network are established, defined and eventually – if found relevant – brought to creation by registered users through a special site named Area 51.[8][9]

User contributions since May 2, 2018 are licensed under Creative Commons Attribution-ShareAlike 4.0 International. Older content, contributed while the site used the Creative Commons Attribution-ShareAlike 3.0 Unported license or the earlier Creative Commons Attribution-ShareAlike 2.5 Unported license, remains licensed under the license in force at the time it was contributed.[5][4][10]

In June 2021, Prosus acquired Stack Overflow for $1.8 billion, its first complete acquisition in the area of educational technology.[11]


Founding and growth

Super User logo

In 2008, Jeff Atwood and Joel Spolsky created Stack Overflow, a question-and-answer web site for computer programming questions, which they described as an alternative to the programmer forum Experts-Exchange.[12] In 2009, they started additional sites based on the Stack Overflow model: Server Fault for questions related to system administration and Super User for questions from computer power users.[13]

In September 2009, Spolsky's company, Fog Creek Software, released a beta version of the Stack Exchange 1.0 platform[2] as a way for third parties to create their own communities based on the software behind Stack Overflow, with monthly fees.[14] This white label service was not successful, with few customers and slow growing communities.[15]

In May 2010, Stack Overflow (as its own new company) raised US$6 million in venture capital from Union Square Ventures and other investors, and it switched its focus to developing new sites for answering questions on specific subjects,[15] Stack Exchange 2.0. Users vote on new site topics in a staging area called Area 51, where algorithms determine which suggested site topics have critical mass and should be created.[12] In November 2010, Stack Exchange site topics in "beta testing" included physics, mathematics, and writing.[16] Stack Exchange publicly launched in January 2011 with 33 Web sites; it had 27 employees[17] and 1.5 million users at the time, and it included advertising.[3] At that time, it was compared to Quora, founded in 2009, which similarly specializes in expert answers.[3] Other competing sites include WikiAnswers and Yahoo! Answers.[18]

In February 2011, Stack Overflow released an associated job board called Careers 2.0, charging fees to recruiters for access, which later re-branded to Stack Overflow Careers.[19] In March 2011, Stack Overflow raised US$12 million in additional venture funding, and the company renamed itself to Stack Exchange, Inc.[20] It is based in Manhattan, New York City .[21] In February 2012, Atwood left the company.[22]

On April 18, 2013 CipherCloud issued Digital Millennium Copyright Act (DMCA) takedown notices in an attempt to block discussion of possible weaknesses of their encryption algorithm.[23][24] The Stack Exchange Crypto group discussion on the algorithm was censored, but it was later restored without pictures.[25]

(As of September 2015), "Stack Exchange" no longer refers to the company, only the network of question-and-answer websites. Instead, the company is now referred to as Stack Overflow.[26]

In 2016, Stack Exchange added a variety of new sites which pushed the boundaries of the typical question-and-answer site.[27] For example, Puzzling offers a platform for users who already know the answer to questions to challenge their peers to solve the problems unlike traditional Q–A sites where the poster does not know the answer.[27]

Declining relationship between users and company

In 2016, Stack Exchange announced the second iteration of the Stack Exchange Quality Project, in which they attempt to implement specific important features requested by the community to meet a distinct high-priority set of goals. After users enthusiastically responded with feature ideas, they complained that there was insufficient action on the company's part.[28]

In October 2018, the company removed its Interpersonal Skills site from the Hot Network Questions list after a complaint on Twitter, and an employee (who was part of the SRE team, which was not community-facing) posted tweets attacking moderators.[29]

Late 2019 controversies

To start, in June 2019, more advertisements were added causing a large dispute.[30] On September 27, 2019, a moderator of multiple Stack Exchange sites, specifically Monica Cellio, was dismissed from her moderator position, allegedly connected to behavior associated with upcoming changes to the Code of Conduct (CoC) relating to gender pronouns.[31][32][33] Many other moderators resigned or suspended their moderator activity in response to the dismissal. The company responded with two very poorly received messages which have since been deleted,[34] and by a slightly less negatively-received apology several days later.[35] In December 2019, the company posted a message, stating that they and the moderator had come to an agreement and expressing regret for any damage to her reputation.[36][37] Nevertheless, this, plus the sudden departure of multiple community managers (Stack Exchange employees who interact with the community), led to an erosion of trust between the community and the company—convincing many of the site's most prolific users, including many community-elected moderators and a community manager, to depart within the next few months.[38][39]

2019–2020 licensing change announcements

On September 2, 2019, the terms of service (and the footer of every page served) changed to referencing the "Creative Commons Attribution-ShareAlike" (CC BY-SA) license's 4.0 version instead of its 3.0 version.[4] Users were puzzled as to how Stack Overflow acquired the rights for this relicensing of their past contributions,[40] with some users explicitly stating that they did not intend their contributions to be licensed under CC BY-SA 4.0.[41][42] Users were concerned that, if the relicensing was found to be a breach of CC BY-SA 3.0, Stack Exchange would have made itself unable to distribute the content under any CC BY-SA license (and that the footer's license statement could be erroneous), and would have to rely on its "perpetual and irrevocable right and license to use, copy, cache, publish, display, distribute, modify, create derivative works and store" the content instead.[43] On September 27, an official Stack Exchange reply stated it had been an "important step", but declined to discuss with the community the legal basis for the relicensing.[44]

In March 2020, a post announced that content contributed before May 2, 2018 was available under a CC BY-SA 3.0 licence.[5] In the ensuing discussion, several users asked about the similar situation in August 2010, when Stack Exchange switched from accepting CC BY-SA 2.5 contributions to 3.0. A representative of the corporation noted "we are looking [...] to show v2.5 for posts predating this change but cannot commit to it yet". Some users were unconvinced that the September 2019 announcement was not a breach of CC BY-SA 3.0 that would have caused its termination, and some answers were not placated by the dateline chosen.[45] In the ensuing discussion, Stack Overflow staff declined to comment.[46]

June - August 2023 moderation strike and outrage

On June 5, 2023, nearly 20% of moderators and over 1,000 high-profile users announced a strike primarily to protest a series of policy changes by Stack Overflow, Inc. and particularly focusing on AI policy changes.[47] The company had rolled out a series of unpopular changes. First, on April 17, the CEO made a controversial blog post about community and AI.[48] This was followed by a series of 5-6 AI tools announcements, on April 19,[49] May 4, May 10, May 18,[50] and June 12/June 15,[51][52] the majority of which were received negatively. Second, on May 22, they announced a new voting button style.[53] Third, AI-generated content had been banned on many sites on the network[54] after the 2022 announcement of the popular large language model ChatGPT; but the company abruptly changed course on May 30[55] and instructed its elected volunteer moderators to effectively allow AI-generated questions and answers.[56] Next, on June 5, the company issued a highly unpopular response to the moderation strike.[57] Then, on June 9, Stack Exchange, Inc. announced that the data dump was not going to be posted,[58] which triggered an outrage and eventually was rolled back on June 16.[59] In addition, on June 20 and then again on June 22, the company posted an announcement of a new prompt design (later changed to GenAI) site, triggering a conflict over the bypassing of the normal site creation process.[60] [61] Following this, on June 29, the company announced a decision to have native ads, causing frustration about Stack Exchange's goals.[62] Next, on July 11, the company announced two new collectives, with much negative feedback on the lack of community around them.[63] Finally, on July 17, Stack Exchange Inc. announced a conference in Berlin, triggering another outrage, this time over the agenda completely overlooking the issue of AI.[64] The strike finally ended with an agreement on August 2 which is considered a victory for the striking users and a defeat for the company, as the company gave into all but one demand with nothing in return.[65]

Site features

Reputation and badges

The primary purpose of each Stack Exchange site is to enable users to post questions and answer them.[16] Users can vote on both answers and questions, and through this process users earn reputation points, a form of gamification.[22][66] This voting system was compared to Digg when the Stack Exchange platform was first released.[14] Users receive privileges by collecting reputation points, ranging from the ability to vote and comment on questions and answers to the ability to moderate many aspects of the site.[66] Due to the prominence of Stack Exchange profiles in web search results and the Stack Overflow Careers job board, users may have reason to game the system.[19] Along with posting questions and answers, users can add comments to them and edit text written by others.[67] Each Stack Exchange site has a "meta" section where users can settle disputes, in the style of MetaFilter's "MetaTalk" forum, because the self-moderation system for questions and answers can lead to significant arguments.[68]

Badges are awarded for asking and answering, participating in meta, and for moderating the site. There are bronze, silver and gold badges and appear on users' profile pages as well as their posts.[69][70]

Moderators and election process

Moderators are responsible for managing the site, such as by following up on flagged posts, locking and protecting posts, suspending users, and deleting the worst posts (including misinformation) on the site. According to the Stack Exchange philosophy, they should be minimally involved in the site. They are also expected to lead by example, as well as to show respect to other users.[71]

To become a moderator, users have to participate in an election. Elections are called as needed by the Stack Exchange Community Team for a designated number of seats. Users must first nominate themselves and have at least 300 reputation (3,000 on Stack Overflow and 1,000 on Math Stack Exchange), while also being in good standing, such as not having been suspended during the past year. Aside from introducing themselves and explaining why they would be a good moderator, users must also answer questions written by the community. Nominations can be withdrawn at any time.[72]

After this, users vote on the candidates in a primary, where the vote tally is made public. The top 10 nominees advance to the election stage, where any user with at least 150 reputation is allowed to vote. A ranked-choice voting system is used where users can rank all the candidates if they wish. Votes are tallied using the Meek STV method (single transferable vote) which allows fractional parts of a vote to be counted.[73]


Stack Exchange allows users to donate some of their reputation to help questions receive answers or better answers, as well as to incentivize users to answer. This is called a 'bounty' and can be applied on questions 48 hours after being asked, lasting for 7 days plus a grace period of 24 hours. The minimum bounty is set at 50 reputation, except if the user has already answered the question or has offered a previous bounty on the question. Bounties cannot be cancelled, and reputation cannot be refunded from a bounty, even if the question did not receive an answer.[74][75]

Technologies used

Stack Exchange uses IIS, SQL Server,[76] and the ASP.NET framework,[76] all from a single code base for every Stack Exchange site (except Area 51, which runs off a fork of the Stack Overflow code base[77]). Blogs formerly used WordPress, but they have been discontinued.[78] The team also uses Redis, HAProxy and Elasticsearch.[76]

Stack Exchange tries to stay up to date with the newest technologies from Microsoft, usually using the latest releases of any given framework. The code is primarily written in C# ASP.NET MVC using the Razor View Engine. The preferred IDE is Visual Studio and the data layers uses Dapper for data access.[79]

The site makes use of URL slugs in addition to numeric identifiers for question URLs.

Site creation process

Every new site created in the Stack Exchange Network goes through a detailed review process on a site called Area 51, that is consisting of four steps:[9][80][81][82]

  • Definition: A public proposal must be drafted and posted so that any member of the community can discuss the proposal and vote on it. This allows a collaborative proposal to emerge over time. The proposal must address these four key issues
    1. the topic of the site
    2. the targeted audience
    3. forty exemplary questions, upvoted at least 10 times from the community
    4. 60 followers from the community
  • Commitment: First, 200 users interested in the new site are asked to formally commit and support the site by actively participating and contributing to it by asking or answering 10 questions during the FIRDR six months of the public beta. Second, 100 users interested in the new site that have committed with over 200 reputation on another site on the network. Finally, it requires a commitment score of 500, which uses the following formula:[83]
    1. PrelimScore = SUM(Reputation >= 200 ? 0.233 * ln(Reputation-101) - 0.75 : 0) + 1.5
    2. UserScore = PrelimScore * 0.9 ^ (DAYS / 180)
  • Beta: A live test version of this site is tested out, in two steps.
  1. Private Beta:If the concept receives 100% commitment (reaches the requirements listed above), the site enters the private beta phase, where committed members begin actively using the site and publicizing it. It must remain for at least 35 days (or 5 weeks).
  2. Public Beta: The site is open to the public for a long period. This allows the creators to ensure that the site reaches critical mass before it is fully launched. It much remain for at least 180 days (or 6 months) of public beta, and 215 total days of beta (31 weeks).
  • Graduation: If the site has at least 1000 open questions, and 70% or more of question have at least 1 upvoted answer, it is granted a "graduation" and fully launched.[84]

Notable users

Nobel Prize winners

Fields Medal winners


Other notable scientists and mathematicians

See also


  1. 2.0 2.1 Mager, Andrew (September 27, 2009). "Find the Answer to Anything with StackExchange". The Web Life. ZDNet. 
  2. 3.0 3.1 3.2 Swartz, Jon (January 24, 2011). "Q&A websites like Quora and Stack Exchange take off". USA Today. 
  3. 4.0 4.1 4.2 "Stack Exchange and Stack Overflow are moving to CC BY-SA 4.0". 
  4. 5.0 5.1 5.2 "An Update On Creative Commons Licensing". 
  5. Atwood, Jeff (May 17, 2009). "A Theory of Moderation". Stack Exchange Blog. 
  6. "All Sites - Stack Exchange". 
  7. "All Sites". Stack Exchange. 
  8. 9.0 9.1 "FAQ – Area 51 – Stack Exchange". Stack Exchange, Inc.. 2014. 
  9. "Legal — Terms of Service". Stack Exchange. December 11, 2014. 
  10. Dummett, Ben (2021-06-02). "WSJ News Exclusive | Stack Overflow Sold to Tech Giant Prosus for $1.8 Billion" (in en-US). Wall Street Journal. ISSN 0099-9660. 
  11. 12.0 12.1 Perez, Sarah (July 8, 2010). "With Debut of Web Apps Q&A Site, Stack Exchange Perfects Automated Site Launch Process". ReadWriteWeb. 
  12. Clarke, Jason (August 20, 2009). "Super User – question and answer site for power users". DownloadSquad. AOL. 
  13. 14.0 14.1 Oshiro, Dana (October 12, 2009). "StackOverflow Shares its Mojo: White Label Q&A for All". ReadWriteWeb. 
  14. 15.0 15.1 Kirkpatrick, Marshall (May 4, 2010). "All-Star Team Backs StackOverflow to Go Beyond Programming Questions". ReadWriteWeb. 
  15. 16.0 16.1 Keller, Jared (November 18, 2010). "Stack Overflow's Crowdsourcing Model Guarantees Success". The Atlantic. 
  16. Jeffries, Adrienne (January 25, 2011). "Forget Quora, New York's Stack Overflow Is Killing It". BetaBeat. 
  17. Jenna Wortham (February 6, 2011). "The Answers Are Out There, and New Q. and A. Sites Dig Them Up". New York Times. 
  18. 19.0 19.1 Needleman, Rafe (February 23, 2011). "Stack Exchange launches programmer recruiting site". CNet. 
  19. Ha, Anthony (March 9, 2011). "Q&A startup Stack Overflow gets new name, more funding". VentureBeat. Reuters. 
  20. Kim, Ryan (February 16, 2011). "Stack Overflow Rides Experts & Order to Q&A Success". GigaOM. 
  21. 22.0 22.1 Finley, Klint (July 5, 2012). "Stack Overflow Man Remakes Net One Answer at a Time". Enterprise (Wired). Retrieved December 16, 2012. 
  22. "CipherCloud used DMCA Takedown on StackExchange discussion of the cryptography". 
  23. "CipherCloud Invokes DMCA To Block Discussions of Its Crypto System". April 21, 2013. 
  24. "How is CipherCloud doing homomorphic encryption". 
  25. Hanlon, Jay (September 15, 2015). "We're Changing Our Name (Back) to Stack Overflow". 
  26. 27.0 27.1 Ericson, Jon (January 26, 2017). "Stack Exchange Year in Review 2016". 
  27. "Answer by user jscs to We need to stop hoping for change in, or help from, SO Inc". 
  28. "Revisiting the "Hot Network Questions" feature, what are our shared goals for having it?". 
  29. "We're testing advertisements across the network" (in en). 
  30. "Firing Mods and Forced Relicensing: Is Stack Exchange Still Interested in Cooperating with the Community?". 2019-09-29. 
  31. "Stack Overflow Inc., sinat chinam, and the goat for Azazel". 2019-09-29. 
  32. "The Mod Firing Squad: Stack Exchange Embroiled in 'He Said, She Said, They Said' Row". October 1, 2019. 
  33. "An Update to our Community and an Apology". 
  34. "An apology to our community, and next steps". 
  35. Update: an agreement with Monica Cellio . Meta Stack Exchange. Retrieved 2020-01-03.
  36. at 22:16, Thomas Claburn in San Francisco Jan 2, 2020. "Stack Overflow makes peace with ousted moderator, wants to start New Year with 2020 vision on codes of conduct" (in en). 
  37. "Firing Community Managers: Stack Exchange is not interested in cooperating with the community, is it?". 
  38. "Firing mods and forced relicensing: is Stack Exchange still interested in cooperating with the community?". 
  39. "Was the retroactive change to CC BY-SA 4.0 approved by Stack Exchange's lawyers?". 
  40. Owens, Thomas. "'I do not grant anyone the right to change the license of my contributions'". 
  41. andreymal. "Review on 'Stack Exchange Data Dump'". 
  42. "Discussion on 'Stack Exchange and Stack Overflow have moved to CC BY-SA 4.0'". 
  43. "Stack Overflow is "unable to pursue dialogues"". 
  44. ""Under CC BY-SA 3.0, any violations terminate (sic) your CC license"". 
  45. "'Stack Overflow staff' declines to comment on licensing situation". 
  46. "Dear Stack Overflow, Inc.". 
  47. "New blog post from our CEO Prashanth: Community is the future of AI" (in en). 
  48. "An example of a generative AI tool: Suggesting better question titles" (in en). 
  49. "AI/ML Tool examples part 3 - Title-Drafting Assistant" (in en). 
  50. "Stack Overflow will be experimenting with a question formatting assistant, and we would love for you to be involved" (in en). 
  51. "We are seeking functional feedback for the formatting assistant" (in en). 
  52. "We are graduating the updated button styling for vote arrows" (in en). 
  53. "Temporary policy: Generative AI (e.g., ChatGPT) is banned" (in en). 
  54. "What is the network policy regarding AI Generated content?" (in en). 
  55. "Some of Stack Overflow's moderators are on strike over its policies allowing AI-generated content". June 13, 2023. 
  56. "Statement from SO: June 5, 2023 Moderator Action" (in en). 
  57. "June 2023 Data Dump is missing" (in en). 
  58. "June 2023 Data Dump is missing" (in en). 
  59. "Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood" (in en). 
  60. "Are you interested in Prompt Design? Join the Community Stakeholders group" (in en). 
  61. "Testing native, sponsored banner ads on Stack Overflow (updated July 13)" (in en). 
  62. "Launching 2 new collectives: PHP and NLP" (in en). 
  63. "Stack Overflow at WeAreDevelopers World Congress in Berlin" (in en). 
  64. "Moderation strike: Results of negotiations". 
  65. 66.0 66.1 "FAQ: What is Reputation?". Stack Overflow. 
  66. Ha, Anthony (May 4, 2010). "Stack Overflow raises $6M to take its Q&A model beyond programming". Deals. VentureBeat. 
  67. Popper, Ben (December 7, 2011). "Conquering the CHAOS of Online Community at Stack Exchange". BetaBeat. 
  68. "Badges". 
  69. "FAQ for Stack Exchange sites". 
  70. "Who are the site moderators, and what is their role here? - Help Center". 
  71. "There's an election going on. What's happening and how does it work?". 
  72. "Could we please clarify just the Primary phase of the election?". 
  73. Co-Founder, Jeff Atwood (2010-06-19). "Improvements to Bounty System" (in en-US). 
  74. "How does the bounty system work?". 
  75. 76.0 76.1 76.2 Craver, Nick (November 22, 2013). "What it takes to run Stack Overflow". 
  76. "Does StackExchange 2.0 Share the Same CodeBase with SO?". 
  77. Grace Note (March 1, 2017). "We will no longer be hosting Blog Overflow". 
  78. "Stack Meta". Stack Meta. 
  79. Sewak, M. (May 18, 2010). "Finding a Growth Business Model at Stack Overflow, Inc.". Stanford CasePublisher (Stanford University School of Engineering) Rev. July 20, 2010 (2010–204–1): 31. 204-2010-1. Retrieved May 23, 2014. 
  80. "Changes to Stack Exchange – Stack Overflow Blog". April 13, 2010. 
  81. "All Proposals - Area 51 - Stack Exchange". 
  82. "Area 51 Commit Percent" (in en). 
  83. "FAQ - Area 51 - Stack Exchange". 
  84. "Gerard 't Hooft". 
  85. "Peter Scholze". 
  86. "Martin Hairer". 
  87. "Terence Tao". 
  88. "Tim Gowers". 
  89. "Curtis McMullen". 
  90. "Richard Borcherds". 
  91. "Edward Witten". 
  92. "Vaughan Jones". 
  93. "Michael Freedman". 
  94. "Bill Thurston". 
  95. "Joel Spolsky". 
  96. "Jeff Attwood". 
  97. "Ravi Vakil". 
  98. "Scott Aaronson". 
  99. "Ian Agol". 
  100. "John Baez". 
  101. "Carlo Beenakker". 
  102. "Andreas Blass". 
  103. "Robert Bryant". 
  104. "Noam Elkies". 
  105. "Matthew Emerton". 
  106. "Alexandre Eremenko". 
  107. "Joesl David Hamkins". 
  108. "James E. Humphreys". 
  109. "Gil Kalai". 
  110. "Anna Krylov". 
  111. "Greg Kuperberg". 
  112. "Tim Peters". 
  113. "Joseph O'Rourke". 
  114. "Igor Rivin". 
  115. "Jeffrey Shallit". 
  116. "Peter Shor". 
  117. "Michael Shulman". 
  118. "Anders Sandberg". 

External links