Mattermost vs Slack
A source-aware comparison of pricing, documented capabilities and workflow fit.
Short answer
- Price: not directly comparable — Mattermost is custom pricing — quote required, Slack is from $8.75/user/mo billed monthly.
- How to start: Mattermost is custom pricing — quote required, Slack is from $8.75/user/mo billed monthly.
- Where they differ: only Mattermost has open source / self-hostable; both offer public api, mobile app and sso (saml).
These lines are generated from the pricing we track, not from a paid placement. How we score tools.
What Mattermost is
What Mattermost isMattermost is team messaging you can run on your own infrastructure, with a Slack-like interface and strong compliance features. Self-hosting is the entire point: message history stays on servers you control, which is what makes it viable for defence, healthcare and regulated finance where a hosted chat service is simply not permitted. The interface is close enough to Slack that migration costs little in training, and the source is open, so the deployment cannot be discontinued from outside.
What Slack is
What Slack isSlack is much more than a chat app; it is the 'digital headquarters' for modern organizations. It eliminates the chaos of internal email by organizing communication into transparent, searchable, and themed channels. With thousands of integrations (GitHub, Jira, Google Drive), Slack centralizes your entire tech stack into one interface. Whether it's a quick voice chat via 'Huddles' or collaborative document editing with 'Canvas,' Slack is designed to keep hybrid and remote teams connected and productive in a fast-paced environment.
Side by side
| Mattermost | Slack | |
|---|---|---|
| Category | Communication | Communication |
| How to start | Quote onlynot a monthly price | $8.75/user/moverified |
| Public API | Yes | Yes |
| Mobile app | Yes | Yes |
| Open source / self-hostable | Yes | No |
| SSO (SAML) | Yes | Yes |
| Visit | Mattermost ↗ | Slack ↗ |
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What Mattermost is built to do
- Self-hosted
- Runs on your own servers or private cloud, with message data never leaving them.
- Open source
- The server is open source, so a deployment cannot be withdrawn by a vendor.
- Compliance export
- Legal hold, audit logging and export formats built for regulated environments.
- Familiar interface
- Channels, threads and integrations close enough to Slack to keep training short.
What Slack is built to do
- Slack Connect
- Securely collaborate with external partners and agencies in shared channels.
- Huddles
- Start instant audio and video sessions with one click for rapid decision-making.
- Workflow Builder
- Automate routine tasks like onboarding or approvals without writing a single line of code.
- Enterprise Security
- Institutional-grade data protection and single sign-on (SSO) support for large firms.
Choose Mattermost if
- Teams that must self-host: Professional is self-hosted and supports a maximum of 250 users
- Organisations needing scale — Enterprise scales to 50,000 concurrent users, Enterprise Advanced to 200,000
- Regulated environments that need compliance export and eDiscovery, available from Enterprise
Skip Mattermost if
- You need a published price — no per-user figure is listed; every tier requires contacting sales
- You are above 250 users but only budgeted for Professional; that tier is capped there
- You need SSO/SAML or guest accounts on the free edition — both start at Professional
Choose Slack if
- Teams on Pro at $7.25 per user/month billed annually ($8.75 monthly) who need unlimited message history
- Small groups testing the Free plan: 90 days of message history, up to 10 apps and 1:1 huddles
- Companies on Business+ at $15 per user/month annually ($18 monthly) that need group external messaging
Skip Slack if
- You rely on the Free plan long term — history is cut at 90 days and apps are capped at 10
- You need Multi-SAML or unlimited workspaces; those are Enterprise+ and priced only by sales
- Your headcount is large: every plan is per user, so cost scales linearly with the team
Evidence and freshness
Where a claim on this page comes from a vendor page, it is linked here.
Mattermost: pros & cons
- Fully self-hostable, including in air-gapped environments
- Familiar channel-based interface
- Open source core
- Ecosystem of integrations is smaller than Slack's
- You carry the upgrade and backup burden
- Mobile apps lag behind commercial rivals
Slack: pros & cons
- Powerful Search: Find any file or message from years ago in a matter of seconds.
- Flexible Channels: Organize work by project, team, or even interests to maintain focus.
- Extensive API: Easily build and integrate your own bots and custom workflows.
- High Reliability: Desktop and mobile apps are exceptionally fast and stable.
- Notification Fatigue: Can be highly distracting if not properly configured by the user.
- Free Plan Limits: Access to message history is restricted on the free tier.
- Enterprise Pricing: Per-user licensing costs can add up quickly for large organizations.
Our verdict on Mattermost
The right call when self-hosting is non-negotiable. Otherwise the convenience gap with hosted chat is wide.
Our verdict on Slack
An indispensable tool for moving team communication away from email and into a faster era.
Published plans, side by side
Every figure below was read from the vendor's own pricing page and is shown with the sentence it came from. Where a vendor publishes no plan prices, we say so rather than guess.
Mattermost
No published plan prices verified. Mattermost either quotes on request or renders its prices in a way we could not read from the pricing page.
Slack
- Free$0/mo
Free $0: 90 days message history, up to 10 apps, 1:1 huddles, 1:1 external messages
- Pro$8.75/user/mo billed monthly
Pro $8.75/user/month monthly or $7.25/user/month annual: unlimited history and apps, group huddles
- Business+$18/user/mo billed monthly
Business+ $18/user/month monthly or $15/user/month annual
Mattermost vs Slack: common questions
- Does Mattermost or Slack have a free plan?
- Mattermost has no free plan listed, while Slack publishes a free plan (Free).
- What is the difference between Mattermost and Slack?
- On the criteria we check, only Mattermost has open source / self-hostable; both offer public api, mobile app and sso (saml). The table above lists every criterion side by side.