Widget UX patterns

An agent widget is a guest in someone else's interface. It inherits their theme, competes with their composer, and gets closed the moment it feels like a different app. Design to the container.

Start with the smallest presentation that lets the user understand the result or finish the task. Request more space only when the workflow demands it.

The four display modes

Inline card

A focused result, a confirmation, or a small set of actions. The default.

• Maximum two primary actions — one primary CTA, one optional secondary.
• No deep navigation, no tabs, no drill-ins inside the card.
• No nested scrolling. Auto-fit content to the available height.
• Never duplicate a feature the host already provides.
• Preserve visual hierarchy: headline → supporting text → CTA.

Mobile: the card may expand its height to match content, up to the height of the mobile display area.

Inline carousel

Scanning a small set of similar, visually rich options — restaurants, playlists, events.

• 3–8 items. Fewer looks broken; more is a list, not a carousel.
• ≤3 lines of metadata per item.
• One clear CTA per item.
• Consistent aspect ratios. A ragged carousel reads as a bug.

Fullscreen

Rich tasks needing room: maps, editing canvases, detailed browsing.

• The host's composer stays overlaid. Design around it — never place controls where the composer lands.
• Do not replicate a native app wholesale. Fullscreen is a focused surface, not a port of your product.
• Provide an obvious way back to inline.
• In M365 Copilot, fullscreen is the only alternate mode supported.

Picture-in-picture

An ongoing activity that should stay visible while the conversation continues — a live session, game, or video.

• Minimal controls. PiP overloaded with chrome is unusable at that size.
• Must react to conversation input, not sit static.
• Auto-closes when the session ends. Do not fight it.

Requesting a mode

const modes = app.getHostContext()?.availableDisplayModes ?? ["inline"];
if (modes.includes("fullscreen") && app.requestDisplayMode) {
  await app.requestDisplayMode({ mode: "fullscreen" });
}

The host may grant a different mode than requested. Render from the mode you were given, never the one you asked for.

Visual design

Color

• Use system colors for text, icons, and structural elements like dividers.
• Brand accents belong on logos, small icons, and the primary button — nothing else.
• Do not override system text color or background with brand color.
• No custom gradients or background overrides.
• Honor hostContext.theme (and prefers-color-scheme as a backstop, since onhostcontextchanged is not universally supported).

Typography

• Inherit the host's font stack. No custom fonts, even in fullscreen.
• Respect device-native sizing rules — SF Pro on iOS, sans-serif on Android.
• Limit size variation; prefer body and body-small.
• Partner styling (bold, italic, highlight) only within content areas.

Layout

• Use the host's grid spacing for cards and collections.
• Consistent padding; never edge-to-edge text.
• Respect safeAreaInsets from host context.
• Drive height with sendSizeChanged / notifyIntrinsicHeight rather than guessing a fixed height.

Icons and imagery

• Monochromatic, outlined iconography that matches the host's language.
• Fixed aspect ratios; never distort.
• Do not render your own logo as a response element — the host appends attribution itself.

Accessibility — non-negotiable

• WCAG AA contrast minimum for text against background.
• Alt text on every image.
• Text resizing must not break layout — no fixed pixel heights around text.
• Full keyboard reachability; visible focus states.
• Semantic elements and ARIA roles (aria-pressed, aria-live for async results). A2UI: plumb AccessibilityAttributes to the native API.
• Respect prefers-reduced-motion.

Loading, empty, and error states

Every widget needs four states, and three of them get skipped.

Interaction with the conversation

• The widget and the chat are one experience. Do not build a parallel chat.
• Use ui/message / sendFollowUpMessage when the user should say something next; use ui/update-model-context when the model just needs to know something. Confusing these produces either a spammy transcript or a model that has no idea what the user selected.
• One meaningful update per user action. Do not stream context on every keystroke.

Localization

The host mirrors locale to document.documentElement.lang.

const locale = document.documentElement.lang || "en-US";

Format dates, numbers, and currency from that locale — not from the server's.

Checklists

Do

• Inline for quick confirmations and simple actions
• Keep the composer usable in fullscreen
• Brand color on accents and badges only
• One clear CTA per carousel item
• Feature-detect before rendering any host-dependent affordance

Don't

• Deep navigation, tabs, or drill-ins inside a card
• Nested scrolling or cramped layouts
• Replicate host-native features
• Override system text colors or backgrounds
• Custom fonts, anywhere
• Overload PiP with controls or leave it static

Related

• host-capability-matrix — which modes and APIs the target host supports.
• ui-state-architecture — preserving presentation state across remounts.
• ui-performance — skeletons, partial input, and offscreen pausing.