diff --git a/.changeset/swingset-tooltip-primitive.md b/.changeset/swingset-tooltip-primitive.md
new file mode 100644
index 00000000000..a845151cc84
--- /dev/null
+++ b/.changeset/swingset-tooltip-primitive.md
@@ -0,0 +1,2 @@
+---
+---
diff --git a/packages/swingset/src/app/layout.tsx b/packages/swingset/src/app/layout.tsx
index 10b6cd9d4c4..09ae389ad1c 100644
--- a/packages/swingset/src/app/layout.tsx
+++ b/packages/swingset/src/app/layout.tsx
@@ -22,13 +22,15 @@ export default function RootLayout({ children }: { children: React.ReactNode })
       suppressHydrationWarning
       className={cn('font-sans', geist.variable)}
     >
-      {process.env.NODE_ENV === 'development' && (
-        <Script
-          src='//unpkg.com/react-grab/dist/index.global.js'
-          crossOrigin='anonymous'
-          strategy='beforeInteractive'
-        />
-      )}
+      <head>
+        {process.env.NODE_ENV === 'development' && (
+          <Script
+            src='//unpkg.com/react-grab/dist/index.global.js'
+            crossOrigin='anonymous'
+            strategy='beforeInteractive'
+          />
+        )}
+      </head>
       <body className='antialiased'>
         <ThemeProvider>
           <ClientRoot>{children}</ClientRoot>
diff --git a/packages/swingset/src/components/DocsViewer.tsx b/packages/swingset/src/components/DocsViewer.tsx
index 083cd38c3ad..94776a2d15e 100644
--- a/packages/swingset/src/components/DocsViewer.tsx
+++ b/packages/swingset/src/components/DocsViewer.tsx
@@ -4,6 +4,7 @@ import dynamic from 'next/dynamic';
 
 const docModules: Record<string, React.ComponentType> = {
   button: dynamic(() => import('../stories/button.mdx')),
+  tooltip: dynamic(() => import('../stories/tooltip.mdx')),
 };
 
 interface DocsViewerProps {
diff --git a/packages/swingset/src/components/StoryCanvas.tsx b/packages/swingset/src/components/StoryCanvas.tsx
index 966ae4997bd..b54b42e8976 100644
--- a/packages/swingset/src/components/StoryCanvas.tsx
+++ b/packages/swingset/src/components/StoryCanvas.tsx
@@ -3,7 +3,7 @@
 import { MosaicProvider } from '@clerk/ui/mosaic/MosaicProvider';
 import type { MosaicVariables } from '@clerk/ui/mosaic/variables';
 import type React from 'react';
-import { useEffect, useState } from 'react';
+import { useEffect, useMemo, useState } from 'react';
 
 import { Tabs, TabsContent, TabsList, TabsTrigger } from '@/components/ui/tabs';
 import { generateKnobs, initKnobValues } from '@/lib/generateKnobs';
@@ -21,18 +21,20 @@ interface StoryCanvasProps {
 export function StoryCanvas({ componentSlug, storySlug }: StoryCanvasProps) {
   const found = findStory(componentSlug, storySlug);
 
-  const [knobs, setKnobs] = useState<KnobRecord>(() => (found ? generateKnobs(found.mod.meta) : {}));
+  // Derive knobs from the slug primitives — `found` is a fresh object every render, so depending
+  // on it (in the effect below) would reset state on every render and loop until React bails out.
+  const knobs = useMemo<KnobRecord>(() => {
+    const entry = findStory(componentSlug, storySlug);
+    return entry ? generateKnobs(entry.mod.meta) : {};
+  }, [componentSlug, storySlug]);
+
   const [knobValues, setKnobValues] = useState<KnobValues>(() => initKnobValues(knobs));
   const [variables, setVariables] = useState<MosaicVariables>({});
 
+  // Reset knob values when the active story (and therefore its knobs) changes.
   useEffect(() => {
-    if (!found) {
-      return;
-    }
-    const nextKnobs = generateKnobs(found.mod.meta);
-    setKnobs(nextKnobs);
-    setKnobValues(initKnobValues(nextKnobs));
-  }, [found, componentSlug, storySlug]);
+    setKnobValues(initKnobValues(knobs));
+  }, [knobs]);
 
   if (!found) {
     return <div className='text-muted-foreground p-8 text-sm'>Story not found.</div>;
diff --git a/packages/swingset/src/components/app-sidebar.tsx b/packages/swingset/src/components/app-sidebar.tsx
index de8b4f42b47..9bad08ac0f7 100644
--- a/packages/swingset/src/components/app-sidebar.tsx
+++ b/packages/swingset/src/components/app-sidebar.tsx
@@ -23,9 +23,75 @@ import { toSlug } from '@/lib/slug';
 
 const groups = getSidebarGroups();
 
-export function AppSidebar({ ...props }: React.ComponentProps<typeof Sidebar>) {
+type ComponentGroupProps = {
+  title: string;
+  componentSlug: string;
+  names: string[];
+};
+
+// One controlled Collapsible per component. The group opens when its route becomes
+// active, but stays user-toggleable otherwise. It must be controlled (not `defaultOpen`)
+// because the instance persists across navigation: `defaultOpen` is only read on init,
+// so a route-derived value mutating later trips Base UI's uncontrolled-state warning.
+function ComponentGroup({ title, componentSlug, names }: ComponentGroupProps) {
   const pathname = usePathname();
+  const docsHref = `/components/${componentSlug}`;
+  const isActive = pathname.startsWith(docsHref);
+  const [open, setOpen] = React.useState(isActive);
+
+  React.useEffect(() => {
+    if (isActive) {
+      setOpen(true);
+    }
+  }, [isActive]);
 
+  return (
+    <Collapsible
+      open={open}
+      onOpenChange={setOpen}
+      className='group/collapsible'
+    >
+      <SidebarGroup>
+        <SidebarGroupLabel
+          className='group/label text-sidebar-foreground hover:bg-sidebar-accent hover:text-sidebar-accent-foreground text-sm'
+          render={<CollapsibleTrigger />}
+        >
+          {title}
+          <ChevronRightIcon className='group-data-open/collapsible:rotate-90 ml-auto transition-transform' />
+        </SidebarGroupLabel>
+        <CollapsibleContent>
+          <SidebarGroupContent>
+            <SidebarMenu>
+              <SidebarMenuItem>
+                <SidebarMenuButton
+                  isActive={pathname === docsHref}
+                  render={<Link href={docsHref} />}
+                >
+                  Overview
+                </SidebarMenuButton>
+              </SidebarMenuItem>
+              {names.map(name => {
+                const href = `/components/${componentSlug}/${toSlug(name)}`;
+                return (
+                  <SidebarMenuItem key={name}>
+                    <SidebarMenuButton
+                      isActive={pathname === href}
+                      render={<Link href={href} />}
+                    >
+                      {name}
+                    </SidebarMenuButton>
+                  </SidebarMenuItem>
+                );
+              })}
+            </SidebarMenu>
+          </SidebarGroupContent>
+        </CollapsibleContent>
+      </SidebarGroup>
+    </Collapsible>
+  );
+}
+
+export function AppSidebar({ ...props }: React.ComponentProps<typeof Sidebar>) {
   return (
     <Sidebar {...props}>
       <SidebarHeader className='flex h-12 justify-center border-b px-4'>
@@ -33,55 +99,14 @@ export function AppSidebar({ ...props }: React.ComponentProps<typeof Sidebar>) {
       </SidebarHeader>
       <SidebarContent className='gap-0'>
         {groups.flatMap(({ stories }) =>
-          stories.map(({ mod, componentSlug, names }) => {
-            const docsHref = `/components/${componentSlug}`;
-            const isOpen = pathname.startsWith(docsHref);
-
-            return (
-              <Collapsible
-                key={mod.meta.title}
-                defaultOpen={isOpen}
-                className='group/collapsible'
-              >
-                <SidebarGroup>
-                  <SidebarGroupLabel
-                    className='group/label text-sidebar-foreground hover:bg-sidebar-accent hover:text-sidebar-accent-foreground text-sm'
-                    render={<CollapsibleTrigger />}
-                  >
-                    {mod.meta.title}
-                    <ChevronRightIcon className='group-data-open/collapsible:rotate-90 ml-auto transition-transform' />
-                  </SidebarGroupLabel>
-                  <CollapsibleContent>
-                    <SidebarGroupContent>
-                      <SidebarMenu>
-                        <SidebarMenuItem>
-                          <SidebarMenuButton
-                            isActive={pathname === docsHref}
-                            render={<Link href={docsHref} />}
-                          >
-                            Overview
-                          </SidebarMenuButton>
-                        </SidebarMenuItem>
-                        {names.map(name => {
-                          const href = `/components/${componentSlug}/${toSlug(name)}`;
-                          return (
-                            <SidebarMenuItem key={name}>
-                              <SidebarMenuButton
-                                isActive={pathname === href}
-                                render={<Link href={href} />}
-                              >
-                                {name}
-                              </SidebarMenuButton>
-                            </SidebarMenuItem>
-                          );
-                        })}
-                      </SidebarMenu>
-                    </SidebarGroupContent>
-                  </CollapsibleContent>
-                </SidebarGroup>
-              </Collapsible>
-            );
-          }),
+          stories.map(({ mod, componentSlug, names }) => (
+            <ComponentGroup
+              key={mod.meta.title}
+              title={mod.meta.title}
+              componentSlug={componentSlug}
+              names={names}
+            />
+          )),
         )}
       </SidebarContent>
       <SidebarRail />
diff --git a/packages/swingset/src/lib/registry.ts b/packages/swingset/src/lib/registry.ts
index 457ef5be4e1..1553e07d988 100644
--- a/packages/swingset/src/lib/registry.ts
+++ b/packages/swingset/src/lib/registry.ts
@@ -1,11 +1,13 @@
 // Import stories explicitly to control order and avoid type casting through unknown.
 import { Disabled, meta as buttonMeta, Primary, Sizes } from '../stories/button.stories';
+import { meta as tooltipMeta, Options as TooltipOptions } from '../stories/tooltip.stories';
 import { toSlug } from './slug';
 import type { StoryModule } from './types';
 
 const buttonModule: StoryModule = { meta: buttonMeta, Primary, Sizes, Disabled };
+const tooltipModule: StoryModule = { meta: tooltipMeta, Options: TooltipOptions };
 
-export const registry: StoryModule[] = [buttonModule];
+export const registry: StoryModule[] = [buttonModule, tooltipModule];
 
 export interface RegistryEntry {
   mod: StoryModule;
diff --git a/packages/swingset/src/stories/tooltip.mdx b/packages/swingset/src/stories/tooltip.mdx
new file mode 100644
index 00000000000..beeedc12c9a
--- /dev/null
+++ b/packages/swingset/src/stories/tooltip.mdx
@@ -0,0 +1,33 @@
+import * as TooltipStories from './tooltip.stories';
+
+# Tooltip
+
+The `Tooltip` component reveals a small label when its trigger is hovered or focused. It wraps any trigger element and positions the bubble with the `side` variant. Focus and blur bubble up from the trigger, so the tooltip is keyboard-accessible without extra wiring.
+
+## Options
+
+<Story
+  name='Options'
+  storyModule={TooltipStories}
+/>
+
+## Usage
+
+```tsx
+import { Tooltip } from '@clerk/ui/mosaic/components/tooltip';
+import { Button } from '@clerk/ui/mosaic/components/button';
+
+<Tooltip
+  content='Tooltip content'
+  side='top'
+>
+  <Button>Hover me</Button>
+</Tooltip>;
+```
+
+## Props
+
+<PropTable
+  meta={TooltipStories.meta}
+  extra={[{ name: 'content', type: 'React.ReactNode' }]}
+/>
diff --git a/packages/swingset/src/stories/tooltip.stories.tsx b/packages/swingset/src/stories/tooltip.stories.tsx
new file mode 100644
index 00000000000..7ff8d672f9b
--- /dev/null
+++ b/packages/swingset/src/stories/tooltip.stories.tsx
@@ -0,0 +1,53 @@
+/** @jsxImportSource @emotion/react */
+import { Button } from '@clerk/ui/mosaic/components/button';
+import type { TooltipProps } from '@clerk/ui/mosaic/components/tooltip';
+import { Tooltip, tooltipStyles } from '@clerk/ui/mosaic/components/tooltip';
+
+import type { StoryMeta } from '@/lib/types';
+
+export const meta: StoryMeta = {
+  group: 'Components',
+  title: 'Tooltip',
+  styles: tooltipStyles,
+};
+
+// Story functions accept Record<string,unknown> (knob values) and cast to TooltipProps.
+// The cast is unavoidable: knobs are dynamically typed; Tooltip has a strict prop interface.
+function knobsAsProps(props: Record<string, unknown>) {
+  return props as unknown as TooltipProps;
+}
+
+export function Options(props: Record<string, unknown>) {
+  return (
+    <div style={{ display: 'flex', gap: 32, alignItems: 'center' }}>
+      <Tooltip
+        {...knobsAsProps(props)}
+        content='On top'
+        side='top'
+      >
+        <Button>Top</Button>
+      </Tooltip>
+      <Tooltip
+        {...knobsAsProps(props)}
+        content='On the right'
+        side='right'
+      >
+        <Button>Right</Button>
+      </Tooltip>
+      <Tooltip
+        {...knobsAsProps(props)}
+        content='On the bottom'
+        side='bottom'
+      >
+        <Button>Bottom</Button>
+      </Tooltip>
+      <Tooltip
+        {...knobsAsProps(props)}
+        content='On the left'
+        side='left'
+      >
+        <Button>Left</Button>
+      </Tooltip>
+    </div>
+  );
+}
diff --git a/packages/ui/src/mosaic/components/tooltip.tsx b/packages/ui/src/mosaic/components/tooltip.tsx
new file mode 100644
index 00000000000..a4028a33b84
--- /dev/null
+++ b/packages/ui/src/mosaic/components/tooltip.tsx
@@ -0,0 +1,96 @@
+/** @jsxImportSource @emotion/react */
+import React from 'react';
+
+import { cva, type VariantProps } from '../cva';
+import { useMosaicTheme } from '../MosaicProvider';
+
+export const tooltipStyles = cva(theme => ({
+  base: {
+    position: 'absolute',
+    zIndex: 50,
+    width: 'max-content',
+    maxWidth: '18rem',
+    paddingInline: theme.spacing(2),
+    paddingBlock: theme.spacing(1),
+    borderRadius: theme.rounded.md,
+    backgroundColor: theme.color.primary,
+    color: theme.color.primaryForeground,
+    fontWeight: 500,
+    ...theme.text('xs'),
+    pointerEvents: 'none',
+    whiteSpace: 'normal',
+  },
+  variants: {
+    side: {
+      top: {
+        bottom: '100%',
+        left: '50%',
+        transform: 'translateX(-50%)',
+        marginBottom: theme.spacing(2),
+      },
+      bottom: {
+        top: '100%',
+        left: '50%',
+        transform: 'translateX(-50%)',
+        marginTop: theme.spacing(2),
+      },
+      left: {
+        right: '100%',
+        top: '50%',
+        transform: 'translateY(-50%)',
+        marginRight: theme.spacing(2),
+      },
+      right: {
+        left: '100%',
+        top: '50%',
+        transform: 'translateY(-50%)',
+        marginLeft: theme.spacing(2),
+      },
+    },
+  },
+  defaultVariants: { side: 'top' },
+}));
+
+export type TooltipProps = Omit<React.ComponentPropsWithRef<'div'>, 'content'> &
+  VariantProps<typeof tooltipStyles> & {
+    /** The content shown inside the tooltip bubble. */
+    content: React.ReactNode;
+  };
+
+/**
+ * Wraps a trigger and reveals `content` on hover or keyboard focus.
+ *
+ * The trigger element is passed as `children`; the tooltip is positioned relative
+ * to it via the `side` variant. Focus and blur bubble up from the trigger, so the
+ * tooltip is reachable by keyboard without extra wiring.
+ */
+export const Tooltip = React.forwardRef<HTMLDivElement, TooltipProps>(function MosaicTooltip(props, ref) {
+  const { side, sx, content, children, ...rest } = props;
+  const theme = useMosaicTheme();
+  const [open, setOpen] = React.useState(false);
+  const tooltipId = React.useId();
+
+  return (
+    <div
+      ref={ref}
+      css={{ position: 'relative', display: 'inline-flex' }}
+      onMouseEnter={() => setOpen(true)}
+      onMouseLeave={() => setOpen(false)}
+      onFocus={() => setOpen(true)}
+      onBlur={() => setOpen(false)}
+      aria-describedby={open ? tooltipId : undefined}
+      {...rest}
+    >
+      {children}
+      {open ? (
+        <div
+          id={tooltipId}
+          role='tooltip'
+          css={tooltipStyles({ side, sx })(theme)}
+        >
+          {content}
+        </div>
+      ) : null}
+    </div>
+  );
+});
