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Communication · Team chat

Slack-style app

Illustrative system design for a team chat app like Slack: 5 topics to read, from requirements to deep dives.

Two copies of the truth, kept honest.

Illustrative design, not Slack’s actual implementation. Arrowbox is not affiliated with Slack’s owner. Disclaimer

Start with Channels and threads Sign in to start readingUpdated 2 Oct 2026

Messaging

  • Channels and threadsIntermediate · 44 min read · Sign in to read

    Sidebar, channel view and a thread side panel, kept in step by one live connection.

  • Unread syncAdvanced · 46 min read · Sign in to read

    One read cursor per channel and thread, kept right across tabs, devices and the title badge.

  • Polls in messagesIntermediate · 42 min read · Sign in to read

    A poll inside a message: instant votes, changing your mind, live tallies and results everyone can read.

  • Message searchIntermediate · 45 min read · Sign in to read

    Filter tokens, scope tabs, safe highlights, paging, and a jump into the channel around the hit.

App shell

  • Workspace boot and offlineAdvanced · 38 min read · Sign in to read

    Open a huge workspace fast: app shell from a service worker, data from IndexedDB, then catch up.