Slack vs Rocket.Chat: An Open-Source Alternative for Enterprises (GDPR-Compliant)

Choosing a platform for team communication today is more than a question of features and convenience - it concerns data protection, data sovereignty, integration capability and long-term operating costs. Especially for companies in regulated industries (e.g. healthcare, finance, public administration), control over the infrastructure and compliance is a decisive criterion.

Slack is widely established as a cloud-based collaboration platform with an extensive integration ecosystem. Rocket.Chat is an open source alternative that allows both self-hosting and managed hosting and prioritizes data control.

Note: In addition to Rocket.Chat, Mattermost is also a strong open source alternative to Slack - both offer self-hosting, GDPR compliance and full data control. Which solution is right for your company depends on your specific requirements.

In this article, we take a careful look at how Slack and Rocket.Chat differ from the perspective of IT decision-makers, system administrators, developers and data protection/compliance officers, particularly with regard to:

• Integration into existing infrastructures
• Architecture, operation and technical feasibility
• Everyday user experience
• Data protection, GDPR and compliance
• Costs, scalability and strategic use

The aim is to provide a sound basis for decision-making - without marketing platitudes.

Table of Contents

• Brief presentation of the solutions
  • Slack
  • Rocket.Chat
• Functional and technical comparison
  • Technical examples and configurations
    • Example: REST API in Rocket.Chat
    • Example: Listing subscriptions via API
    • Example: Real-time API (WebSockets / DDP)
    • Example: Slack bot with Bolt (Node.js)
• User experience and practice in day-to-day business
• Data protection and GDPR
  • Location of data processing and third country risks
  • Legal basis and risks
  • Technical protective measures and best practices
• Operation and costs
  • Operating concepts
  • License models and cost structure
  • Effort: Updates, Monitoring, Support
  • Scaling and cost development
• Conclusion and recommendation
  • Recommendation scenarios
• Our services for your communication infrastructure
  • Consulting and conception
  • Installation and setup
  • Operation and maintenance
• Contact us
• Sources and further links

Brief presentation of the solutions

Slack

• Manufacturer & license model Slack Technologies (now part of Salesforce) offers Slack as a proprietary SaaS solution. It is mainly used via subscriptions (Freemium, Standard, Plus, Enterprise). (Wikipedia: Slack)
• Architecture (Cloud / Self-Hosted / Hybrid) Slack exists exclusively as a hosted service - a user cannot host Slack themselves or control the infrastructure.
• Target groups & application scenarios Teams, start-ups, medium-sized and larger companies that want a quick start, a wide range of integrations and minimal in-house operation.
• Technological basis & community Slack relies on web, desktop and mobile clients; developers use the Slack Web API, Events API, SDKs (e.g. Bolt). The community mainly participates through app development in the app directory.
• Main advantages & restrictions ✅ Very good user-friendliness, high reliability and numerous integrations ✅ Little operational effort for the company ❌ No influence on infrastructure, no control over data storage ❌ License costs can increase significantly with growing user numbers ❌ Data protection risks for data outside the EU

Rocket.Chat

• Manufacturer & license model Rocket.Chat Technologies operates the project with an open source core (MIT license) and offers additional enterprise functions and support options for a fee. (Wikipedia: Rocket.Chat)
• Architecture (Cloud / Self-Hosted / Hybrid) Rocket.Chat can be self-hosted (e.g. Docker, Kubernetes or bare metal), alternatively operated as a managed instance or in a hybrid setup. (Rocket.Chat Documentation)
• Target groups & application scenarios Organizations with high data protection and compliance requirements, public institutions, companies with a desire for data sovereignty.
• Technological basis & community Rocket.Chat is implemented in TypeScript / Node.js, typically with MongoDB as the database. Custom extensions can be developed in TypeScript via the apps engine. (Developer Documentation) The community is active - there are numerous plugins, integrations and contributions.
• Main advantages & restrictions ✅ Full control over infrastructure and data ✅ Open source, white labeling, customizability ✅ Flexible deployment options ❌ Own responsibility for operation, updates, scaling ❌ Initial investment in infrastructure and expertise required ❌ Some features may have to be supplemented by in-house development

Functional and technical comparison

Technical examples and configurations

Example: REST API in Rocket.Chat

# Example: Send message via webhook
curl -X POST https://chat.example.com/hooks/incoming/ABC123 \
  -H "Content-Type: application/json" \
  -d '{
    "text": "Build successfully completed",
    "channel": "#deployments"
  }'

This uses the Rocket.Chat webhook system. (Integrations Documentation)

Example: Listing subscriptions via API

GET /api/v1/subscriptions.get
Authorization: Bearer <access_token>

This recalls subscriptions (e.g. channels, direct messages). (API Documentation)

Example: Real-time API (WebSockets / DDP)

const socket = new WebSocket("wss://chat.example.com/websocket");
socket.onopen = () => {
  socket.send(JSON.stringify({
    msg: "connect",
    version: "1",
    support: ["1", "pre2", "pre1"]
  }));
  // Further method calls and subscriptions ...
};

Rocket.Chat documents this in its real-time API documentation.

Example: Slack bot with Bolt (Node.js)

const { App } = require('@slack/bolt');
const app = new App({
  token: process.env.SLACK_BOT_TOKEN,
  signingSecret: process.env.SLACK_SIGNING_SECRET
});

app.command('/hello', async ({ command, ack, say }) => {
  await ack();
  await say(`Hello <@${command.user_id}>`);
});

app.start(process.env.PORT || 3000);

This is a typical introduction to Slack bot programming (see Slack developer documentation).

These examples show typical integrations: Webhooks, REST endpoints, real-time communication.

User experience and practice in day-to-day business

For example, a survey on G2 shows that users tend to rate Slack higher than Rocket.Chat in areas such as usability and integration (Slack 9.5 vs. Rocket.Chat 8.7). However, such ratings rarely take into account the operational overhead and data protection aspects.

Data protection and GDPR

Location of data processing and third country risks

Slack stores data in data centers, often outside the EU, which means that access scenarios potentially subject to US laws (e.g. the CLOUD Act) are possible.

Rocket.Chat, on the other hand, allows complete hosting in the EU, which means that external third country access can be largely excluded - provided it is configured correctly.

Legal basis and risks

• Schrems II & EU-US data transfer: The ECJ has ruled that transfers to the USA are only legally secure with additional guarantees (e.g. standard contractual clauses, data protection impact assessment).
• Art. 28 GDPR (order processing): For SaaS services such as Slack, the provider acts as a processor; the customer must conclude AV contracts and ensure that data protection requirements are met.
• Access by authorities / CLOUD Act: US authorities could demand access if Slack (or the operator) is registered in the USA, even if data is routed via EU servers.

Technical protective measures and best practices

• Encryption: TLS for data traffic, encryption of data at rest (e.g. AES), ideally end-to-end encryption (if supported)
• Access controls & roles: Granular assignment of rights, principle of least privilege
• Audit logging: logging of all administrative actions, traceability of changes
• Data minimization & retention: Guidelines for the automatic deletion of old messages or files
• Hosting in the EU / self-hosting: Reduces the risk of third country access
• Security updates & patch management: Ensure self-hosting on your own responsibility

The self-hosting option with Rocket.Chat gives the company (or operator) full control over security architecture, access chains and compliance requirements - an advantage over pure SaaS solutions.

Operation and costs

Operating concepts

• Slack: Fully managed service; operation, scaling, updates and monitoring are handled by Slack itself
• Rocket.Chat: The operator (company or managed provider) is responsible for infrastructure, high availability, backups, scaling and update processes

License models and cost structure

• Slack: Freemium model, graduated subscriptions per user/month
• Rocket.Chat: core version as open source (free of charge), enterprise and support functions for a fee

Effort: Updates, Monitoring, Support

Rocket.Chat requires the installation of monitoring tools (e.g. Prometheus, Grafana), implementation of backup strategies, update routines and security patching.

With Slack, this effort is eliminated, but without insight into the infrastructure.

Scaling and cost development

With Slack, license costs rise in proportion to the number of users. With Rocket.Chat, infrastructure and operating costs increase with growing user and load volumes - but often with better planning and scope for optimization.

Conclusion and recommendation

Slack scores highly in terms of user-friendliness, reliable SaaS operating modalities and a mature integration ecosystem. For many companies, it is the pragmatic choice when data protection requirements are moderate and rapid implementation is important.

Rocket.Chat offers a powerful alternative with more control over data, infrastructure and adaptability - ideal for organizations with high data protection requirements and sufficient resources to manage operations and scaling themselves.

Alternative to Slack: In addition to Rocket.Chat, Mattermost also offers a sophisticated open source solution for team communication with self-hosting options, LDAP/OIDC integration and full GDPR compliance.

Recommendation scenarios

Our services for your communication infrastructure

WZ-IT supports you in the implementation of your team communication solution - whether Rocket.Chat, Mattermost or Slack:

Consulting and conception

• Analysis of your communication and compliance requirements
• Evaluation: Rocket.Chat vs. Mattermost vs. Slack
• Architecture design for scalability and high availability
• Migration strategy for existing systems

Installation and setup

• On-premise in your data center
• Private cloud on dedicated servers
• Hybrid solutions according to your requirements
• Cluster setup with high availability
• Integration into existing IT infrastructure (LDAP, SSO, etc.)

Operation and maintenance

• 24/7 monitoring
• Automatic backups
• Security updates
• Performance tuning & optimization
• User administration & support
• SLA with guaranteed availability

Contact us

Would you like to switch from Slack to Rocket.Chat or Mattermost or set up a secure communication platform? We will be happy to advise you on the right solutions.

📅 Book your free and non-binding initial consultation: Schedule appointment

📞 Phone: +49 2922 875068 📧 Email: [email protected]

We look forward to your inquiry!

Sources and further links

• Rocket.Chat – API Reference (REST, Realtime)
• Rocket.Chat – Integrations & Webhooks
• Rocket.Chat – Realtime API Documentation
• Rocket.Chat – Developer Documentation
• Rocket.Chat – Official comparison page to Slack
• Slack (Software) – Wikipedia
• Rocket.Chat (Software) – Wikipedia
• Slack vs Rocket.Chat – Comparison report on SoftwareAdvice
• Rocket.Chat vs Slack – G2 Comparison
• Comparison of Open Source Alternatives – Rocket.Chat Blog Post
• CLOUD Act – EU Commission
• GDPR – Art. 28 ff. (EUR-Lex)