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Slack is acloud-based team communication platform developed bySlack Technologies, which has been owned bySalesforce since 2020. Slack uses afreemium model. Slack is primarily offered as abusiness-to-business service, with its userbase being predominantly team-based businesses while its functionalities are focused primarily on business administration and communication.[7][8]
Slack originated as an internal communication tool used withinStewart Butterfield's companyTiny Speck, during its work on the development ofGlitch, an online video game.[9] These communication tools were initially built around theInternet Relay Chat (IRC) protocol and included scripts designed to automate and organize file exchanges among its development team. By October 2012, Stewart Butterfield realized thatGlitch was not going to bring necessary profits.[10] As a result, he decided to change the direction of his company and repurpose the communication tools they had developed into a new product.
In 2012, Butterfield decided to name their upcoming product "Slack", which he said was derived from the phrase "Searchable Log of All Conversation and Knowledge", replacing the previous codename "linefeed".[11]
In August 2013, Slack was launched to the public[12] and continued to maintain compatibility withIRC, reflecting its origin.[13] Additionally, it was also compatible withXMPP messaging protocols. In May 2018 however, the company chose to close down these corresponding gateways due to limitations inherent in those protocols.[14]
On July 26, 2018, Slack acquiredHipChat andStride fromAtlassian, with plans to shut down both services in February 2019 and migrate their users to Slack.[15][16]
In June 2019, Slack went public through adirect public offering to reach a market value of $19.5 billion.[17]
In July 2020, Slack acquired Rimeto, a startup specializing in employee directories and profiles, with plans to rename the service and operate it as a standalone app.[18][19] Almost a year later, in June 2021, its functionality was launched as an optional feature within Slack named "Slack Atlas".[20]
On December 1, 2020, Slack andSalesforce announced an agreement for Salesforce to acquire the company for approximately $27.7 billion, marking one of the most significant tech acquisitions at that time.[21][22] The acquisition was completed on July 21, 2021.[23]
On December 5, 2022, Salesforce announced that Butterfield was leaving Slack and would be succeeded byLidiane Jones, an executive vice president at Salesforce.[24] On November 13, 2023, Salesforce executive Denise Dresser was appointed to replace Jones, who was in turn replacingWhitney Wolfe Herd asBumble CEO.[25][26]
In August 2024,Box and Slack announced an expanded partnership that introduced secure AI capabilities to enterprise content management.[27][28]
In March 2015, Slack announced that it had beenhacked for over four days in February 2015 and that some data associated with user accounts had been compromised, including email addresses, usernames, hashed passwords, phone numbers, andSkype IDs. In response to the attacks, Slack addedtwo-factor authentication to its service.[29]
On January 4, 2021, Slack suffered a significant outage that lasted several hours. From 10 AM ET until 3 PM ET, users could not log in, send or receive messages, place or answer calls, or use Slack connections. After 3 PM, most of the core features became operational, except for push notifications, email, and third-party integrations, includingGoogle Calendar andOutlook Calendar.[30][31]
In 2022, Slack suffered widely reported outages on February 22,[32] March 9[33] and July 26.[34] On 31 December 2022, Slack announced that its privateGitHub repositories had been compromised during the previous weeks, using stolen security tokens.[35]
In February 2025, Slack experienced a widely reported outage.[36]
Slack offers manyIRC-style features, including persistent chat rooms known as channels, which are organized by topic, as well as private groups and direct-messaging functionalities.[37] All content, including files, conversations, and people, is searchable within Slack. Users can express their reactions in the form ofemojis to any message.[38] Message history on Slack is limited to messages from the last 90 days on the free plan.[39]
Slack allows communities, groups, or teams to join a "workspace" via a specific URL or invitation sent by a team admin or owner.[40] A workspace can contain both public and private channels, with public channels being accessible to all members of the workspace.[41] Both public and private channels can be converted interchangeably.[42]
Direct messages enable users to engage in private one-on-one or group conversations with up to nine participants. Group direct message can be converted into a private channel.[43]
Slack integrates with many third-party services and supports community-built integrations, includingGoogle Drive,Trello,Dropbox,Box,Heroku,IBM Bluemix,Crashlytics,GitHub,Runscope,Zendesk, andZapier.[44][45] In July 2015, Slack launched an integration with Google Calendar.[46] Later, in December of the same year, a searchable directory was introduced, consisting of over 150 integrations that users can install.[47] In addition to these integrations, Slack offers users the ability to incorporate and customizechatbots known as "Slackbots". These chatbots can be configured to send notifications, reminders, or provide tailored responses to specific phrases, among other functions.[48] Furthermore, Slack provides anapplication programming interface that enables users to develop applications and automate various processes, including sending notifications based on input, generating alerts for specific conditions, creating internal support tickets, and more.[49]
In March 2018, Slack partnered withWorkday, a financial andhuman capital management firm.[50][51] This integration allows employees to access co-worker information, organizational charts, benefits, feedback, and time-off requests within Slack.[52]
In March 2022, Slack introduced a newvoice conference feature known as "Huddles".[53] Within a Huddle, users have the capability to mute or unmute themselves,share their screens, draw on a shared screen, and invite others to the call.[54] In June 2022, Huddles received the additional functionality of video calls.[55] Huddles are restricted to only two participants on free tiers, while paid plans offer the capacity for up to 50 participants.
In March 2023, Salesforce announced the partnership withOpenAI to launch aChatGPT integration for Slack that can be used for summarizing conversations, answering questions, or drafting replies.[56]
Slack provides mobile apps foriOS andAndroid in addition to their web browser client and desktop clients for MacOS, Windows,[57] and Linux (beta).[58] Slack is also available for theApple Watch, allowing users to send direct messages, see mentions, and make simple replies.[59]
Slack is afreemium product whose main paid features are the ability to search more than 90 days' archived messages and add unlimited apps and integrations.[39] They also claim support for an unlimited number of users. WhenfreeCodeCamp attempted to switch its community of over 8,000 users to Slack in 2015, however, they experienced many technical issues and were advised by Slack support to limit their channels to "no more than 1,000 users (ideally more like 500)".[60][61] That specific limit no longer applied by January 2017.[62]
In August 2013, 8,000 customers signed up for the service within 24 hours of its launch.[12][63] In February 2015, the company reported that approximately 10,000 new daily active users had signed up each week, and had more than 135,000 paying customers spread across 60,000 teams.[64][65] By April 2015, those numbers had grown to 200,000 paid subscribers and a total of 750,000 daily active users.[66] Late in 2015, Slack passed more than a million daily active users.[67][68] As of May 2018[update], Slack had over 8 million daily users, 3 million of whom had paid accounts.[69] At the time of itsS-1 filing forIPO, dated April 26, 2019, Slack reported more than 10 million daily active users from more than 600,000 organizations, located in more than 150 countries.[70]
In 2019, it was estimated that employees at large firms were sending over 200 Slack messages per week on average.[71] From 2013 to 2019 the amount of time spent on work email had declined, which was attributed to the proliferation of Slack and its competitorsSymphony (launched in 2014),Workplace (launched in 2016),Microsoft Teams (launched 2017) andGoogle Hangouts Chat and Meet (launched in 2018).[71]
In March 2015, theFinancial Times wrote that Slack was the first business technology to have crossed from business into personal use sinceMicrosoft Office and theBlackBerry.[72] In 2017,New York magazine criticized the platform for being "another utility we both rely on and resent".[73]
In 2017, Slack was recognized as the best startup of the year at theCrunchies Awards, organized byTechCrunch.[74]
The digital rights groupElectronic Frontier Foundation (EFF) has cautioned that "Slack stores and is able to read all of your communications, as well as identifying information for everyone in your workspace."[75] They commended the company for following several best practices in standing up for users concerning government data requests, such as requiring a warrant for content stored on its server, and awarding it four out of five stars in its 2017 "Who has your back" report;[76] the EFF also criticized Slack for "a broad set of exceptions" to its promise to notify users of such requests, and for other privacy shortcomings.[75]
Slack has been criticized by users[77] for storing user data exclusively oncloud servers under Slack control.[78][79] This is found to be a particular issue for users with large teams, who experienced issues with connectivity within the app, access to archived messages, and the number of users for a given "workspace".[80]
Slack has also been criticized for a retroactive 2018 change to its privacy policy, allowing access to all public and private chat messages by workspace administrators, without the need of consent from any parties using the app.[81] According to the new policy, Slack workspace members are no longer notified when data is downloaded from their workspace.[82]
Slack has also been criticized when used infree and open-source projects for the inability to search for messages and discussions.[83][84]
Interview with Slack co-founder Stewart Butterfield:Kai Ryssdal; Maria Hollenhorst (July 22, 2019)."What Is Slack?".Marketplace. American Public Media. RetrievedAugust 10, 2019.
