On
Jul 29, 2025
Slack isn’t just about messaging — it’s about navigating hundreds of conversations without drowning. The sidebar isn’t decoration — it’s infrastructure. It manages context, urgency, and personal flow, all in one column.
Let’s decode how Slack’s sidebar became the brain behind its user experience.
Unread = Intent, Not Just Activity
Takeaway: Urgency should be programmable. Slack teaches users to manage their own chaos via subtle defaults.
Unreads are weighted: bold (priority), light gray (seen but not urgent), hidden (muted)
Mentions and threads are grouped, not scattered
Channels with activity but no mentions don’t demand attention
Memory Between Workspaces
Takeaway: Great UX isn’t just fast — it’s continuous. Memory is a form of speed.
Sidebar remembers last opened channel in each workspace
Preserves scroll position, collapsed sections, and custom ordering
No cognitive reset when switching contexts
Custom Sections as Mental Models
Takeaway: Let users define their operating system. Structure unlocks scale.
Users can sort channels into collapsible sections
Each section behaves like a mini-dashboard
Personal order > system order
Contextual Surfacing, Not Overload
Takeaway: Smart defaults > feature overload. Great navigation removes options, not adds them.
Infrequently used channels auto-hide
Sidebar surfaces based on recent use and urgency
No need to micromanage — it adapts quietly
Mentions & Threads = Triage Center
Takeaway: Slack doesn’t make you “check everything” — it gives you lanes of control.
Structured like an emergency lane
Threads = async memory, @mentions = urgent interrupts
DMs float to the top when active