primitives
Builds and customizes assistant-ui chat UI from composable, unstyled @assistant-ui/react primitives that follow Radix-style part composition. Use when assembling or styling a custom Thread, Composer, message rendering, action bar, or branch picker from building blocks: ThreadPrimitive (.Root, .Viewport, .Messages, .Empty, .ScrollToBottom), ComposerPrimitive (.Input, .Send, .Cancel, .Attachments), MessagePrimitive (.Parts/.Content, .Error), ActionBarPrimitive (.Copy, .Edit, .Reload, .Speak, feedback, .ExportMarkdown), BranchPickerPrimitive, AttachmentPrimitive, ThreadListPrimitive, ThreadListItemPrimitive. Covers MessagePrimitive.Parts children render functions for text, image, reasoning, and tool-call parts; conditional rendering with AuiIf (deprecated .If); and gotchas like wrapping in AssistantRuntimeProvider and adding className since primitives ship unstyled. For prebuilt drop-in UI and scaffolding use setup; for multi-thread sidebar behavior use thread-list.
What this skill does
# assistant-ui Primitives
**Always consult [assistant-ui.com/llms.txt](https://www.assistant-ui.com/llms.txt) for the latest API.**
Composable, unstyled components following Radix UI patterns.
## References
- [./references/thread.md](./references/thread.md) -- ThreadPrimitive deep dive
- [./references/composer.md](./references/composer.md) -- ComposerPrimitive deep dive
- [./references/message.md](./references/message.md) -- MessagePrimitive deep dive
- [./references/action-bar.md](./references/action-bar.md) -- ActionBarPrimitive deep dive
- [./references/part-grouping.md](./references/part-grouping.md) -- Part grouping and chain-of-thought UI
- [./references/mentions.md](./references/mentions.md) -- Composer mentions and slash commands
## Import
```tsx
import {
AuiIf,
ThreadPrimitive,
ComposerPrimitive,
MessagePrimitive,
ActionBarPrimitive,
BranchPickerPrimitive,
AttachmentPrimitive,
ThreadListPrimitive,
ThreadListItemPrimitive,
} from "@assistant-ui/react";
```
## Primitive Parts
| Primitive | Key Parts |
|-----------|-----------|
| `ThreadPrimitive` | `.Root`, `.Viewport`, `.Messages`, `.Empty`, `.ScrollToBottom` |
| `ComposerPrimitive` | `.Root`, `.Input`, `.Send`, `.Cancel`, `.Attachments` |
| `MessagePrimitive` | `.Root`, `.Parts`/`.Content`, `.If`, `.Error` |
| `ActionBarPrimitive` | `.Copy`, `.Edit`, `.Reload`, `.Speak`, `.FeedbackPositive`, `.FeedbackNegative`, `.ExportMarkdown` |
| `BranchPickerPrimitive` | `.Previous`, `.Next`, `.Number`, `.Count` |
## Custom Thread Example
```tsx
function CustomThread() {
return (
<ThreadPrimitive.Root className="flex flex-col h-full">
<ThreadPrimitive.Empty>
<div className="flex-1 flex items-center justify-center">
Start a conversation
</div>
</ThreadPrimitive.Empty>
<ThreadPrimitive.Viewport className="flex-1 overflow-y-auto p-4">
<ThreadPrimitive.Messages>
{({ message }) =>
message.role === "user" ? (
<CustomUserMessage />
) : (
<CustomAssistantMessage />
)
}
</ThreadPrimitive.Messages>
</ThreadPrimitive.Viewport>
<ComposerPrimitive.Root className="border-t p-4 flex gap-2">
<ComposerPrimitive.Input className="flex-1 rounded-lg border px-4 py-2" />
<ComposerPrimitive.Send className="bg-blue-500 text-white px-4 py-2 rounded-lg">
Send
</ComposerPrimitive.Send>
</ComposerPrimitive.Root>
</ThreadPrimitive.Root>
);
}
```
## Conditional Rendering
Prefer `AuiIf` for new code. Primitive `.If` components still exist but are deprecated.
```tsx
<AuiIf condition={({ message }) => message.role === "user"}>
User only
</AuiIf>
<AuiIf condition={({ thread }) => thread.isRunning}>
Generating...
</AuiIf>
<AuiIf condition={({ message }) => message.branchCount > 1}>
Has edit history
</AuiIf>
<AuiIf condition={({ thread }) => thread.isRunning}>
<ComposerPrimitive.Cancel>Stop</ComposerPrimitive.Cancel>
</AuiIf>
<AuiIf condition={({ thread }) => thread.isEmpty}>No messages</AuiIf>
```
## Message Parts (children render function)
As of 0.14, primitives that render lists (`ThreadPrimitive.Messages`, `MessagePrimitive.Parts`, `ThreadPrimitive.Suggestions`, `ThreadListPrimitive.Items`, `ComposerPrimitive.Attachments`) take a children render function instead of a `components` prop. The `components` prop still works but is deprecated.
`MessagePrimitive.Parts` is the canonical name (`MessagePrimitive.Content` is a deprecated alias).
```tsx
<MessagePrimitive.Parts>
{({ part }) => {
switch (part.type) {
case "text":
return <p>{part.text}</p>;
case "image":
return <img src={part.image} alt="" />;
case "reasoning":
return (
<details>
<summary>Thinking</summary>
{part.text}
</details>
);
case "tool-call":
return part.toolUI ?? <div>Tool: {part.toolName}</div>;
default:
return null; // registered tool/data UIs still render
}
}}
</MessagePrimitive.Parts>
```
Returning `null` from the render function lets registered tool and data UIs render via the registry; return `<></>` to explicitly render nothing.
## Branch Picker
```tsx
<AuiIf condition={({ message }) => message.branchCount > 1}>
<BranchPickerPrimitive.Root className="flex items-center gap-1">
<BranchPickerPrimitive.Previous>←</BranchPickerPrimitive.Previous>
<span><BranchPickerPrimitive.Number /> / <BranchPickerPrimitive.Count /></span>
<BranchPickerPrimitive.Next>→</BranchPickerPrimitive.Next>
</BranchPickerPrimitive.Root>
</AuiIf>
```
## Common Gotchas
**Primitives not rendering**
- Wrap in `AssistantRuntimeProvider`
- Ensure parent primitive provides context
**Styles not applying**
- Primitives are unstyled by default
- Add `className` and style with your app's Tailwind/CSS system
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