diff --git a/packages/ui/README.md b/packages/ui/README.md
new file mode 100644
index 00000000..2437fdaf
--- /dev/null
+++ b/packages/ui/README.md
@@ -0,0 +1,239 @@
+# @bytelyst/ui
+
+Shared component library for the ByteLyst ecosystem. Built with Radix UI primitives, Lucide icons, and CSS custom properties from `@bytelyst/design-tokens`.
+
+## Install
+
+```bash
+pnpm add @bytelyst/ui
+```
+
+Peer dependencies: `react`, `react-dom`.
+
+## Components (15)
+
+### Button
+
+5 variants (`primary`, `secondary`, `ghost`, `destructive`, `outline`), 3 sizes, loading state with spinner.
+
+```tsx
+import { Button } from '@bytelyst/ui';
+
+<Button variant="primary" size="md" loading={saving}>Save</Button>
+<Button variant="destructive" onClick={onDelete}>Delete</Button>
+<Button variant="ghost" size="sm">Cancel</Button>
+```
+
+### Input
+
+Text input with error/success states. Supports `aria-invalid` automatically when `error` is truthy.
+
+```tsx
+import { Input } from '@bytelyst/ui';
+
+<Input placeholder="Email" type="email" />
+<Input error="Required field" />
+```
+
+### Textarea
+
+Auto-resize textarea with error states.
+
+```tsx
+import { Textarea } from '@bytelyst/ui';
+
+<Textarea placeholder="Description" rows={4} />;
+```
+
+### Select
+
+Styled `<select>` with keyboard navigation.
+
+```tsx
+import { Select } from '@bytelyst/ui';
+
+<Select
+  options={[
+    { value: 'a', label: 'Option A' },
+    { value: 'b', label: 'Option B' },
+  ]}
+  value={selected}
+  onChange={setSelected}
+/>;
+```
+
+### Modal / Dialog
+
+Radix `@radix-ui/react-dialog` with focus trap, Esc close, and `aria-modal`.
+
+```tsx
+import { Modal } from '@bytelyst/ui';
+
+<Modal open={isOpen} onOpenChange={setOpen} title="Edit item">
+  <p>Modal content here</p>
+</Modal>;
+```
+
+### ConfirmDialog
+
+Radix AlertDialog for destructive/warning confirmations. Supports async `onConfirm`.
+
+```tsx
+import { ConfirmDialog } from '@bytelyst/ui';
+
+<ConfirmDialog
+  open={showConfirm}
+  onOpenChange={setShowConfirm}
+  title="Delete item?"
+  description="This action cannot be undone."
+  onConfirm={handleDelete}
+  variant="destructive"
+/>;
+```
+
+### Toast
+
+4 types (`success`, `error`, `warning`, `info`), auto-dismiss, `role="alert"`. Use `ToastProvider` in your root layout and `toast()` anywhere.
+
+```tsx
+import { ToastProvider, toast } from '@bytelyst/ui';
+
+// In providers.tsx
+<ToastProvider>{children}</ToastProvider>;
+
+// Anywhere in app
+toast('Saved successfully', 'success');
+toast('Something went wrong', 'error');
+```
+
+### Card
+
+Container with `default`, `elevated`, and `interactive` variants. Includes `CardHeader`, `CardTitle`, `CardDescription` sub-components.
+
+```tsx
+import { Card, CardHeader, CardTitle, CardDescription } from '@bytelyst/ui';
+
+<Card>
+  <CardHeader>
+    <CardTitle>Dashboard</CardTitle>
+    <CardDescription>Overview of your data</CardDescription>
+  </CardHeader>
+  {children}
+</Card>;
+```
+
+### Badge
+
+Status/count/risk-level badges, color-coded by semantic tokens.
+
+```tsx
+import { Badge } from '@bytelyst/ui';
+
+<Badge variant="success">Active</Badge>
+<Badge variant="danger">Critical</Badge>
+<Badge variant="warning" count={5} />
+```
+
+### EmptyState
+
+Placeholder for empty lists with icon, description, and optional CTA.
+
+```tsx
+import { EmptyState } from '@bytelyst/ui';
+
+<EmptyState
+  icon={<FileText size={48} />}
+  title="No items yet"
+  description="Create your first item to get started."
+  action={<Button onClick={onCreate}>Create</Button>}
+/>;
+```
+
+### Label
+
+Styled form label.
+
+```tsx
+import { Label } from '@bytelyst/ui';
+
+<Label htmlFor="email">Email address</Label>;
+```
+
+### Separator
+
+Horizontal/vertical divider.
+
+```tsx
+import { Separator } from '@bytelyst/ui';
+
+<Separator />
+<Separator orientation="vertical" />
+```
+
+### Sidebar
+
+Responsive collapsible sidebar with mobile toggle, overlay, and navigation items.
+
+```tsx
+import { Sidebar, SidebarItem } from '@bytelyst/ui';
+
+<Sidebar
+  collapsed={collapsed}
+  onToggle={() => setCollapsed(!collapsed)}
+  header={<span>MyApp</span>}
+  footer="v1.0.0"
+>
+  <SidebarItem href="/dashboard" label="Dashboard" icon={<Home size={18} />} active />
+  <SidebarItem href="/settings" label="Settings" icon={<Settings size={18} />} />
+</Sidebar>;
+```
+
+### StatCard
+
+Dashboard metric card with trend indicator.
+
+```tsx
+import { StatCard } from '@bytelyst/ui';
+
+<StatCard label="Total Users" value="1,234" trend="up" trendValue="+12%" />
+<StatCard label="Errors" value={42} trend="down" trendValue="-8%" icon={<AlertCircle />} />
+```
+
+### LoadingSpinner
+
+Accessible loading indicator with `aria-busy` and `prefers-reduced-motion` support.
+
+```tsx
+import { LoadingSpinner } from '@bytelyst/ui';
+
+<LoadingSpinner size="md" label="Loading data…" />
+<LoadingSpinner size="sm" label="" />  {/* spinner only, no text */}
+```
+
+## Design Token Integration
+
+All components use CSS custom properties with `--bl-` prefix and sensible fallbacks. Override them per-product:
+
+```css
+:root {
+  --bl-accent: var(--jj-accent); /* JarvisJr */
+  --bl-surface-card: var(--fm-surface); /* FlowMonk */
+}
+```
+
+## Accessibility
+
+Every component includes:
+
+- `focus-visible` ring styles
+- ARIA attributes (`aria-label`, `aria-modal`, `aria-busy`, `aria-invalid`, `aria-current`)
+- Keyboard navigation (Esc to close, Tab focus trap in modals)
+- `prefers-reduced-motion` respected via Tailwind's `animate-spin`
+
+## Storybook
+
+```bash
+pnpm --filter @bytelyst/ui storybook
+```
+
+Storybook is configured with `@storybook/addon-a11y` for automated accessibility checks.
diff --git a/packages/ui/package.json b/packages/ui/package.json
index b5a9eabb..6d6c7cfc 100644
--- a/packages/ui/package.json
+++ b/packages/ui/package.json
@@ -19,7 +19,10 @@
     "./card": "./src/components/Card.tsx",
     "./label": "./src/components/Label.tsx",
     "./select": "./src/components/Select.tsx",
-    "./separator": "./src/components/Separator.tsx"
+    "./separator": "./src/components/Separator.tsx",
+    "./sidebar": "./src/components/Sidebar.tsx",
+    "./stat-card": "./src/components/StatCard.tsx",
+    "./loading-spinner": "./src/components/LoadingSpinner.tsx"
   },
   "peerDependencies": {
     "react": "^18.0.0 || ^19.0.0",
diff --git a/packages/ui/src/components/LoadingSpinner.tsx b/packages/ui/src/components/LoadingSpinner.tsx
new file mode 100644
index 00000000..7b6cf6d7
--- /dev/null
+++ b/packages/ui/src/components/LoadingSpinner.tsx
@@ -0,0 +1,35 @@
+import * as React from 'react';
+import { clsx } from 'clsx';
+import { Loader2 } from 'lucide-react';
+
+export interface LoadingSpinnerProps {
+  size?: 'sm' | 'md' | 'lg';
+  label?: string;
+  className?: string;
+}
+
+export function LoadingSpinner({
+  size = 'md',
+  label = 'Loading…',
+  className,
+}: LoadingSpinnerProps) {
+  const sizes: Record<string, string> = {
+    sm: 'h-4 w-4',
+    md: 'h-6 w-6',
+    lg: 'h-8 w-8',
+  };
+
+  return (
+    <div
+      role="status"
+      aria-busy="true"
+      aria-label={label}
+      className={clsx('flex items-center justify-center gap-2', className)}
+    >
+      <Loader2 className={clsx(sizes[size], 'animate-spin text-[var(--bl-accent,#5A8CFF)]')} />
+      {label && <span className="text-sm text-[var(--bl-text-secondary,#a0a0b0)]">{label}</span>}
+    </div>
+  );
+}
+
+LoadingSpinner.displayName = 'LoadingSpinner';
diff --git a/packages/ui/src/components/Sidebar.tsx b/packages/ui/src/components/Sidebar.tsx
new file mode 100644
index 00000000..de3ee256
--- /dev/null
+++ b/packages/ui/src/components/Sidebar.tsx
@@ -0,0 +1,110 @@
+'use client';
+
+import * as React from 'react';
+import { clsx } from 'clsx';
+import { Menu, X } from 'lucide-react';
+
+export interface SidebarProps {
+  children: React.ReactNode;
+  header?: React.ReactNode;
+  footer?: React.ReactNode;
+  collapsed?: boolean;
+  onToggle?: () => void;
+  className?: string;
+  width?: number;
+}
+
+export function Sidebar({
+  children,
+  header,
+  footer,
+  collapsed = false,
+  onToggle,
+  className,
+  width = 240,
+}: SidebarProps) {
+  return (
+    <>
+      {/* Mobile toggle */}
+      {onToggle && (
+        <button
+          className={clsx(
+            'fixed top-3 left-3 z-[38] flex items-center justify-center w-10 h-10 rounded-lg',
+            'border border-[var(--bl-border,#2a2a4a)] bg-[var(--bl-bg-elevated,#12151c)]',
+            'text-[var(--bl-text-primary,#fff)] cursor-pointer',
+            'md:hidden'
+          )}
+          onClick={onToggle}
+          aria-label={collapsed ? 'Open menu' : 'Close menu'}
+          type="button"
+        >
+          {collapsed ? <Menu size={20} /> : <X size={20} />}
+        </button>
+      )}
+
+      {/* Overlay */}
+      {onToggle && !collapsed && (
+        <div
+          className="fixed inset-0 z-[39] bg-black/50 md:hidden"
+          onClick={onToggle}
+          aria-hidden="true"
+        />
+      )}
+
+      <aside
+        aria-label="Primary"
+        className={clsx(
+          'flex flex-col h-full border-r shrink-0 transition-transform duration-200',
+          'border-[var(--bl-border,#2a2a4a)] bg-[var(--bl-bg-elevated,#12151c)]',
+          'fixed md:static z-40',
+          collapsed ? '-translate-x-full md:translate-x-0' : 'translate-x-0',
+          className
+        )}
+        style={{ width, minWidth: width }}
+      >
+        {header && <div className="border-b border-[var(--bl-border,#2a2a4a)] p-4">{header}</div>}
+
+        <nav aria-label="Main navigation" className="flex-1 overflow-y-auto p-2">
+          {children}
+        </nav>
+
+        {footer && (
+          <div className="border-t border-[var(--bl-border,#2a2a4a)] p-4 text-xs text-[var(--bl-text-secondary,#a0a0b0)]">
+            {footer}
+          </div>
+        )}
+      </aside>
+    </>
+  );
+}
+
+export interface SidebarItemProps {
+  href: string;
+  label: string;
+  icon?: React.ReactNode;
+  active?: boolean;
+  className?: string;
+}
+
+export function SidebarItem({ href, label, icon, active, className }: SidebarItemProps) {
+  return (
+    <a
+      href={href}
+      aria-current={active ? 'page' : undefined}
+      className={clsx(
+        'flex items-center gap-2.5 px-3 py-2 rounded-md text-sm transition-colors',
+        'focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-[var(--bl-accent,#5A8CFF)]',
+        active
+          ? 'bg-[var(--bl-surface-card,#1a1a2e)] text-[var(--bl-text-primary,#fff)] font-semibold'
+          : 'text-[var(--bl-text-secondary,#a0a0b0)] hover:bg-[var(--bl-surface-muted,#252540)] hover:text-[var(--bl-text-primary,#fff)]',
+        className
+      )}
+    >
+      {icon && <span className="shrink-0">{icon}</span>}
+      <span>{label}</span>
+    </a>
+  );
+}
+
+Sidebar.displayName = 'Sidebar';
+SidebarItem.displayName = 'SidebarItem';
diff --git a/packages/ui/src/components/StatCard.tsx b/packages/ui/src/components/StatCard.tsx
new file mode 100644
index 00000000..fe67cf59
--- /dev/null
+++ b/packages/ui/src/components/StatCard.tsx
@@ -0,0 +1,65 @@
+import * as React from 'react';
+import { clsx } from 'clsx';
+import { TrendingUp, TrendingDown, Minus } from 'lucide-react';
+
+export interface StatCardProps {
+  label: string;
+  value: string | number;
+  trend?: 'up' | 'down' | 'flat';
+  trendValue?: string;
+  icon?: React.ReactNode;
+  className?: string;
+}
+
+export function StatCard({ label, value, trend, trendValue, icon, className }: StatCardProps) {
+  const TrendIcon = trend === 'up' ? TrendingUp : trend === 'down' ? TrendingDown : Minus;
+
+  return (
+    <div
+      className={clsx(
+        'rounded-xl border p-5',
+        'bg-[var(--bl-surface-card,#1a1a2e)] border-[var(--bl-border,#2a2a4a)]',
+        className
+      )}
+    >
+      <div className="flex items-start justify-between">
+        <div>
+          <p className="text-xs font-medium text-[var(--bl-text-secondary,#a0a0b0)] mb-1">
+            {label}
+          </p>
+          <p className="text-2xl font-bold text-[var(--bl-text-primary,#fff)]">{value}</p>
+        </div>
+        {icon && (
+          <div className="rounded-lg p-2 bg-[var(--bl-surface-muted,#252540)] text-[var(--bl-text-secondary,#a0a0b0)]">
+            {icon}
+          </div>
+        )}
+      </div>
+
+      {trend && trendValue && (
+        <div className="flex items-center gap-1 mt-3 text-xs">
+          <TrendIcon
+            size={14}
+            className={clsx(
+              trend === 'up' && 'text-[var(--bl-success,#34D399)]',
+              trend === 'down' && 'text-[var(--bl-danger,#FF6E6E)]',
+              trend === 'flat' && 'text-[var(--bl-text-secondary,#a0a0b0)]'
+            )}
+          />
+          <span
+            className={clsx(
+              'font-medium',
+              trend === 'up' && 'text-[var(--bl-success,#34D399)]',
+              trend === 'down' && 'text-[var(--bl-danger,#FF6E6E)]',
+              trend === 'flat' && 'text-[var(--bl-text-secondary,#a0a0b0)]'
+            )}
+          >
+            {trendValue}
+          </span>
+        </div>
+      )}
+    </div>
+  );
+}
+
+StatCard.displayName = 'StatCard';
diff --git a/packages/ui/src/index.ts b/packages/ui/src/index.ts
index ebb731cd..21fc0f20 100644
--- a/packages/ui/src/index.ts
+++ b/packages/ui/src/index.ts
@@ -17,3 +17,11 @@ export { Card, CardHeader, CardTitle, CardDescription, type CardProps } from './
 export { Label, type LabelProps } from './components/Label.js';
 export { Select, type SelectProps } from './components/Select.js';
 export { Separator, type SeparatorProps } from './components/Separator.js';
+export {
+  Sidebar,
+  SidebarItem,
+  type SidebarProps,
+  type SidebarItemProps,
+} from './components/Sidebar.js';
+export { StatCard, type StatCardProps } from './components/StatCard.js';
+export { LoadingSpinner, type LoadingSpinnerProps } from './components/LoadingSpinner.js';