Slack

Definition: The dominant business messaging platform, organized around channels rather than individual chats, and one of the most integration-friendly tools in business software. Founded in 2009 by Stewart Butterfield (co-founder of Flickr) and team as a byproduct of building an online game called Glitch — the internal chat tool they built to coordinate the game’s development ended up more valuable than the game itself, and Slack launched publicly in 2013. It grew explosively among tech companies, IPO’d via a direct listing in 2019, and was acquired by Salesforce in 2021 for roughly $27.7 billion, after which it continued operating as a distinct product folded into Salesforce’s broader collaboration strategy.

Core Services & Concepts

Incoming Webhooks — Webhook, one of the most iconic and widely copied webhook implementations in software: POST a JSON payload to a unique URL and it appears as a message in a channel
OAuth 2.0 (Slack Apps) — OAuth 2.0, scoped bot and user tokens control exactly which APIs (messages, files, channels) an installed app can access
Socket Mode / RTM API — WebSocket, real-time message delivery for apps that can’t expose a public HTTPS endpoint for the older Events API
Slash commands & Block Kit — custom /command triggers plus a structured JSON layout language (Block Kit) for building interactive messages with buttons, menus, and forms directly inside Slack
Workflow Builder — no-code internal automations (form submission → post to channel → notify a person) built without needing a bot or external server
Enterprise Grid & SSO — SSO (Single Sign-On), large organizations run multiple connected workspaces under one Enterprise Grid org, with centralized identity, data-loss-prevention, and compliance controls layered on top of individual workspace admin
Canvas — persistent, editable documents pinned inside a channel or DM for shared notes, project trackers, or onboarding info, blurring the line between chat and lightweight docs

How Pricing Works

Free plan commonly caps message history at around the most recent 90 days and limits the workspace to roughly 10 connected apps and 1:1 huddles only
Pro plan is billed per active user monthly (roughly $7-9/user/month on an annual plan), unlocking full searchable history and group huddles
Business+ adds SSO, compliance exports, and an uptime SLA, priced above Pro on a per-user basis
Enterprise Grid is custom-negotiated pricing for large organizations running many connected workspaces under one central admin console
Billing is strictly per “active” user — someone who posted or read a message in the billing cycle — so seat costs can fluctuate month to month unlike flat per-seat SaaS pricing
Nonprofit and educational organizations can qualify for discounted or free Pro-tier pricing through Slack’s nonprofit program

Pros

Widely regarded as the most polished, responsive chat interface among business messaging tools
Extremely rich integration ecosystem, with thousands of apps in the Slack App Directory plus a mature bot/webhook API for custom tooling
Channel-based organization scales well for large teams when channel naming and archiving conventions are enforced
Became the default expectation for business chat, especially at tech companies and startups
Slack Connect lets separate companies share channels directly with each other without juggling guest accounts
Strong search across messages, files, and canvases makes it easy to resurface old decisions and context, especially on paid tiers with full history

Cons

Notification overload and channel sprawl are common complaints without active workspace governance
Pricing scales with active users, and message history is capped or purged on lower tiers, a common surprise for smaller teams
Huge integration surface area means a single overly broad OAuth-scoped app can become a real security exposure if compromised
Native video/meeting tooling (Huddles) is generally considered weaker than Microsoft Teams’ or Zoom’s dedicated meeting features
Now owned by Salesforce, so long-term product direction is increasingly tied to Salesforce’s enterprise strategy rather than an independent roadmap
Capped message history on free and lower tiers means institutional knowledge can quietly become unsearchable once older messages age out

Comparison: Slack vs Microsoft Teams

	Slack	Microsoft Teams
Primary strength	Polished UX and third-party integration ecosystem	Deep Microsoft 365 bundling and enterprise identity/compliance
Typical pricing model	Per-active-user monthly tiers (Free / Pro / Business+ / Enterprise Grid)	Bundled into Microsoft 365 suites, or standalone Teams Essentials per user
Best fit	Tech-forward teams wanting fast UX and many integrations	Organizations already standardized on Microsoft 365/Windows
API or product style	REST + Events API/Socket Mode, Block Kit for interactive messages	Microsoft Graph REST API, Adaptive Cards, tied to Entra ID

Best For

Team communication for companies of any size, especially ones relying on many third-party integrations, bots, and custom internal tooling
Tech-forward organizations wanting fast, informal, channel-based communication with minimal IT overhead

Real Examples

The primary internal communication tool at most modern tech companies and startups, including well-known engineering orgs at IBM, Airbnb, and Pinterest
Countless open-source projects and developer communities run public Slack workspaces for support and contributor coordination
Salesforce itself runs much of its own internal communication on Slack following the 2021 acquisition
Widely used by nonprofit and open-source foundations for community coordination under Slack’s discounted nonprofit pricing program

Use Cases

Team chat and cross-team coordination
Bot and integration notifications, like CI/CD or monitoring alerts
Customer-facing shared channels via Slack Connect
Lightweight internal workflow automation via Workflow Builder
Community and support channels for open-source projects or customer bases
Onboarding and knowledge-base pages via Canvas, covering some lightweight internal-wiki use cases

Integration Notes & Common Pitfalls

Incoming Webhooks are one-way (post-only) and tied to a single channel; use the full Web API with a bot token instead if the integration needs to read messages, react, or update existing ones
Bot tokens and user tokens carry different OAuth scopes, installing an app with broader scopes than it actually needs (e.g. channels:history when only chat:write is required) is a common unnecessary security exposure
Slash commands and interactive Block Kit components require a public HTTPS endpoint (or Socket Mode) that acknowledges within Slack’s short response timeout, slow backend work needs to be deferred and followed up asynchronously
Rate limits (Rate Limiting) apply per method and per workspace pricing tier, bursty notification integrations like CI pipelines can hit them if requests aren’t batched or throttled
Apps distributed publicly through the Slack App Directory must pass Slack’s app review process, which checks requested OAuth scopes and data handling before listing

Code Example

// Posting a message to a Slack channel via an Incoming Webhook
await fetch(process.env.SLACK_WEBHOOK_URL, {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({
    text: 'Deploy finished: v2.4.1 shipped to production',
    blocks: [
      {
        type: 'section',
        text: { type: 'mrkdwn', text: '*Deploy finished:* `v2.4.1` shipped to production' },
      },
    ],
  }),
});

FAQ

Why did Slack pivot away from being a video game company? Slack’s founding team originally built Glitch, an online game that failed to find a sustainable audience, but the internal chat tool they built to coordinate its development turned out to be more valuable than the game, so they shut Glitch down and turned the tool into a product.

Is Slack still run independently after the Salesforce acquisition? Slack operates as a Salesforce product now, positioned as the interface layer for Salesforce’s broader “Customer 360” strategy, but it still runs largely as its own brand, app directory, and codebase rather than being absorbed into Salesforce’s UI.

What happens to old messages on Slack’s free tier? Message history is commonly capped at around the most recent 90 days on the free plan — older messages typically become inaccessible rather than permanently deleted, and upgrading to a paid plan restores access to the full history.

Can Slack fully replace a team wiki? Not entirely — Canvas and pinned messages cover lightweight documentation, but most teams still pair Slack with a dedicated tool like Notion or Confluence for long-form, structured knowledge.

History

Founded in 2009 by Stewart Butterfield (co-founder of Flickr) and team, originally built as an internal tool while developing an online multiplayer game called Glitch
Glitch shut down in 2012, but the team spun its internal chat tool into Slack, which launched publicly in 2013 and grew rapidly among tech companies
IPO’d via a direct listing on the NYSE in 2019, an unusual path that skipped a traditional underwritten offering
Acquired by Salesforce in 2021 for roughly $27.7 billion, one of the largest software acquisitions at the time and Salesforce’s biggest deal to date
Launched Slack Connect in 2020, letting separate companies message and collaborate directly across their own Slack workspaces without either side needing guest accounts

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