Use reactions for lightweight emoji feedback anchored to an existing item, comments for written discussion, mentions for routing attention to a person or group, and activity feed for catch-up across work events.
Use reactions for lightweight emoji feedback anchored to an existing item, comments for written discussion, mentions for routing attention to a person or group, and activity feed for catch-up across work events.
Practice the judgment: Imagine this situation: A thumbs-up reaction is treated as approval even though approver eligibility, version, audit, and rejection paths are missing. Write the person's goal, choose one of these patterns, and show the state that helps the person continue. Use the decision rules and source trail below to explain your choice.
Review the underlying principle →| Dimension | Reactions | Comments | Mentions | Threaded discussion | Activity feed | Notification center | Presence |
|---|---|---|---|---|---|---|---|
| UI or UX | UI + UX - Lightweight emoji feedback control anchored to an existing message, comment, issue, document selection, or work item | UI + UX - Object-attached comment composer and comment list with authorship, replies, state, permissions, and moderation | UI + UX - Inline recipient reference with autocomplete, stable recipient identity, notification routing, access checks, and broad-audience safeguards | UI + UX - Topic-centered conversation with parent post, reply branches, unread participation state, and thread-level controls | UI + UX - Catch-up stream of recent collaboration and work events with actor, verb, object, type, destination, and triage controls | UI + UX - Durable user-opened notification history and action drawer | UI + UX - Person or group availability signal with status label, recency, source, privacy boundary, and action-aware affordances |
| UI guidance | Render reactions as compact chips or controls attached to a specific item, showing emoji or reaction name, count, the current user's selected state, add-reaction access, remove behavior, and a way to inspect who reacted. | Render comments as anchored contributions with author identity, timestamp, body, optional attachment or selection context, edited state, reply target, and state labels such as open, resolved, hidden, deleted, or assigned. | Show mention suggestions at the caret with names, handles, avatars, teams, channels, availability or scope hints, permission warnings, and keyboard-highlight state; distinguish exact matches, ambiguous display names, unavailable recipients, and broad-audience mentions. | Render a threaded discussion around a visible parent topic or parent message, with reply rows that preserve author, timestamp, reply target, branch depth, unread or new state, and thread-scoped actions. | Render activity feed as a typed event stream where each item names the actor or source app, action, object, workspace or channel, timestamp, preview, event type, read or cleared state when supported, and a stable destination for follow-up. | Provide a persistent notification entry point, usually a bell or inbox control, with a count that represents new unseen notifications rather than every unread item forever. | Show presence controls and explanations where users act on the signal: status menu, status duration, last updated time, working-hours note, privacy restriction, stale value, co-viewer list, and action changes such as call disabled, message allowed, or notify later. |
| UX guidance | Protect interpretation by making add/remove reversible, avoiding overloading one emoji with hidden meaning, grouping noisy reactions in activity feeds, and routing consequential decisions to stronger patterns. | Preserve comment drafts, anchors, authorship, notifications, edit history, deletion outcomes, and resolved or hidden states so conversation context remains trustworthy across reloads, permissions, moderation, and return visits. | Use mentions when a user needs to call attention to a person, team, channel, role, or group from inside a message, comment, task, document, issue, or thread while keeping the reference embedded in the authored content. | Use threaded discussion when users need to follow, contribute to, or resolve a conversation that branches from one topic, question, channel message, or post and must keep replies understandable over time. | Protect attention by grouping low-value repetition, preserving meaningful actors and destinations, distinguishing mention/reply/reaction/app/reminder/project-change types, and routing audit evidence, long-form content, and live status elsewhere. | Use a notification center when users receive enough asynchronous system or collaboration updates that they need a durable place to review, triage, and act later. | Use presence when users need to decide whether to interrupt, wait, route work, join a session, assign follow-up, or understand who is currently viewing or recently active in a shared space. |
| Good UI | A message row shows 👍 6, 👀 2, and Add reaction; the user's 👍 is highlighted, clicking it removes their reaction, and opening the count reveals who reacted. | A document margin comment shows the selected paragraph, author, timestamp, body text, Reply, Resolve, Assign, and Copy link actions with the composer focused on that selection. | A comment composer opens a suggestion list after @, shows people and teams with avatars, handles, access labels, and keyboard focus, then inserts a mention chip for Priya Rao. | A support topic shows the original question, three top-level replies, one expanded reply branch, an accepted answer badge, unread branch marker, and thread-level Follow and Mute controls. | A team activity feed shows Priya mentioned you in #refunds, Build bot marked release-128 failed, Maya reacted to your handoff note, and Rahul merged PR #742, each with icon, timestamp, preview, type filter, and Open action. | A bell opens a drawer with Unread and All filters, showing comment mentions, approval requests, export results, and background-job failures in newest-first order. | A reviewer row shows Priya as Busy in a meeting until 14:30, disables Call, keeps Message available, and offers Notify when available. |
| Bad UI | The same user can add duplicate reactions because already-reacted errors are ignored. | A Notes textarea sits under a record and calls itself comments even though every user overwrites the same field. | Mention chips break when copied, pasted, edited, localized, or rendered in plain-text fallbacks. | Nested replies are indented until they become unreadable on mobile and the answer is hidden below collapsed context. | A feed includes every presence heartbeat and typing event, making mentions and failed deployment events impossible to find. | Users ignore the center because duplicate low-value messages inflate the badge. | A stale active badge remains after the user has gone offline and the call button still looks primary. |
| Good UX | A teammate adds 👀 to show they are looking at a message, sees their reaction highlighted, removes it after replying, and the activity feed groups the reaction event with other low-priority reactions. | A reviewer comments on a selected line, adds an action item for Dana, receives a reply, resolves the comment, and can reopen it from the resolved filter. | A user mentions @Dana in a private incident note, sees that Dana lacks access, chooses Invite and mention, and the resulting notification opens the exact note. | A user opens a notification to a specific unread reply, sees the parent post and branch context, replies, marks the answer, and mutes future replies after resolution. | A user filters Activity to mentions and replies, answers one thread inline, clears low-value reactions, saves a custom view for VIPs, and opens a deployment failure in the source app. | Opening the notification drawer clears the new-notification badge while unread items remain available for later triage. | A file owner sees who has viewed the document within the same domain, respects hidden view-history settings, and uses the signal for follow-up rather than audit proof. |
| Bad UX | A user adds ✅ as casual acknowledgement, but an automation silently closes the task. | A user writes a long comment, loses network connection, and the draft disappears when the page reloads. | A mention notification opens the record homepage rather than the exact comment sentence, forcing the recipient to search for why they were pulled in. | A moderator marks an answer but the thread summary still shows unanswered because answer state is stored only on the visible reply card. | A user clears a notification in Activity but the notification center badge stays out of sync and the same event reappears as unread. | Users mark all notifications read and lose the only record of an export job they still need to download. | A manager treats Away as an attendance record even though it came from device inactivity and privacy-limited activity data. |
| Best fit | Users need quick, lightweight feedback on an existing message, comment, issue, document selection, or work item. | Feedback must preserve author, timestamp, reply, resolution, assignment, or moderation context. | Composed content needs to target people or groups inline. | A topic or parent message can generate multiple reply branches that users need to follow over time. | Users need to catch up on recent collaboration, app, repository, channel, project, meeting, reminder, or task activity. | Users receive multiple asynchronous updates across objects, jobs, collaborators, approvals, or reminders. | Users need to understand current or recent availability before messaging, calling, assigning, routing, or joining. |
| Avoid when | The response needs written reasoning, evidence, or a reply thread. | The user is simply entering a long answer into a form field. | The user is selecting a structured owner, assignee, approver, or recipient field outside written content. | The surface is a broad feed of independent posts or activity cards. | The surface is primarily content consumption, media browsing, or article-like stream reading. | The product has only occasional current-action feedback that a toast or inline status can handle. | The product needs a durable audit trail or compliance record. |
| Required state | One reaction added by current user state. | Empty comment list and first-comment composer. | Highlighted suggestion, keyboard-selected suggestion, mouse or touch-selected suggestion, and inserted mention token. | Parent topic or parent message with author, timestamp, title or body, category, and reply count. | Default feed state with actor, verb, object, timestamp, source, type icon, preview, scope, and destination for each activity item. | Closed entry-point state with zero, new-unseen, and unread-but-seen counts. | Manual status, automatic status, status duration, status message, working-hours state, paused-notification state, and calendar-derived state. |
| Accessibility burden | Give each reaction chip an accessible name that includes emoji meaning, count, selected state, and target item context. | Label the comments region with the object or selection being discussed. | Expose the suggestion list as a labelled popup tied to the editor and announce the number of available mention targets. | Label the thread region with the parent topic or message title. | Give the activity feed a heading and expose the current filter, layout, and unread or cleared state in text. | Announce new notification arrival with status semantics when appropriate, but avoid interrupting users repeatedly for low-priority center items. | Announce meaningful presence changes only when they affect the current task or selected person. |
| Common misuse | Hiding add reaction behind pointer hover only. | Using one shared Notes field as a comment system and overwriting prior contributors. | Treating a mention suggestion list as a generic people picker and ignoring caret position, inline serialization, and notification side effects. | Flattening every reply into a chronological stream and losing who replied to whom. | Dumping every low-level system event, presence update, typing event, or cursor movement into the feed. | Treating the badge count, unread count, and total notification count as one number. | Treating presence as employee monitoring or audit evidence. |