diff --git a/packages/iios-messaging-ui/package.json b/packages/iios-messaging-ui/package.json
index 754f846..78d31d1 100644
--- a/packages/iios-messaging-ui/package.json
+++ b/packages/iios-messaging-ui/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@insignia/iios-messaging-ui",
-  "version": "0.1.8",
+  "version": "0.1.9",
   "type": "module",
   "main": "dist/index.js",
   "module": "dist/index.js",
diff --git a/packages/iios-messaging-ui/src/components/composer.test.tsx b/packages/iios-messaging-ui/src/components/composer.test.tsx
new file mode 100644
index 0000000..c6947f8
--- /dev/null
+++ b/packages/iios-messaging-ui/src/components/composer.test.tsx
@@ -0,0 +1,71 @@
+import { describe, it, expect, vi } from 'vitest';
+import { render, screen, fireEvent, waitFor } from '@testing-library/react';
+import { Composer } from './composer';
+
+function mount(onSend = vi.fn().mockResolvedValue(undefined)) {
+  render(<Composer members={[]} canUpload={false} upload={vi.fn()} onSend={onSend} />);
+  return { onSend, box: screen.getByLabelText('Message') as HTMLTextAreaElement };
+}
+
+describe('<Composer /> formatting + native text services', () => {
+  it('is a textarea with the platform spellchecker enabled', () => {
+    const { box } = mount();
+    expect(box.tagName).toBe('TEXTAREA');
+    // The red squiggle + right-click suggestions come from the OS via these attributes.
+    expect(box.getAttribute('spellcheck')).toBe('true');
+    expect(box.getAttribute('autocorrect')).toBe('on');
+  });
+
+  it('Enter sends, Shift+Enter does not (it makes a newline)', async () => {
+    const { onSend, box } = mount();
+    fireEvent.change(box, { target: { value: 'hello' } });
+
+    fireEvent.keyDown(box, { key: 'Enter', shiftKey: true });
+    expect(onSend).not.toHaveBeenCalled();
+
+    fireEvent.keyDown(box, { key: 'Enter' });
+    await waitFor(() => expect(onSend).toHaveBeenCalledWith('hello', expect.anything()));
+  });
+
+  it('does not send mid-IME composition', () => {
+    const { onSend, box } = mount();
+    fireEvent.change(box, { target: { value: 'にほん' } });
+    fireEvent.keyDown(box, { key: 'Enter', isComposing: true });
+    expect(onSend).not.toHaveBeenCalled();
+  });
+
+  it('a toolbar button wraps the current selection in its marker', () => {
+    const { box } = mount();
+    fireEvent.change(box, { target: { value: 'make me bold' } });
+    box.setSelectionRange(8, 12); // "bold"
+    fireEvent.click(screen.getByLabelText('Bold (⌘B)'));
+    expect(box.value).toBe('make me *bold*');
+  });
+
+  it('⌘B / ⌘I wrap the selection too', () => {
+    const { box } = mount();
+    fireEvent.change(box, { target: { value: 'hello world' } });
+    box.setSelectionRange(0, 5);
+    fireEvent.keyDown(box, { key: 'b', metaKey: true });
+    expect(box.value).toBe('*hello* world');
+
+    box.setSelectionRange(8, 13); // "world" shifted by the two markers
+    fireEvent.keyDown(box, { key: 'i', ctrlKey: true });
+    expect(box.value).toBe('*hello* _world_');
+  });
+
+  it('with nothing selected, a marker pair is inserted at the caret', () => {
+    const { box } = mount();
+    fireEvent.change(box, { target: { value: 'ab' } });
+    box.setSelectionRange(2, 2);
+    fireEvent.click(screen.getByLabelText('Italic (⌘I)'));
+    expect(box.value).toBe('ab__');
+  });
+
+  it('sends the raw markers as plain text — formatting is a render concern', async () => {
+    const { onSend, box } = mount();
+    fireEvent.change(box, { target: { value: 'ship *today*' } });
+    fireEvent.keyDown(box, { key: 'Enter' });
+    await waitFor(() => expect(onSend).toHaveBeenCalledWith('ship *today*', expect.anything()));
+  });
+});
diff --git a/packages/iios-messaging-ui/src/components/composer.tsx b/packages/iios-messaging-ui/src/components/composer.tsx
index 0437cfa..20ecc33 100644
--- a/packages/iios-messaging-ui/src/components/composer.tsx
+++ b/packages/iios-messaging-ui/src/components/composer.tsx
@@ -1,4 +1,4 @@
-import { useMemo, useRef, useState, type ChangeEvent, type FormEvent, type KeyboardEvent } from 'react';
+import { useEffect, useMemo, useRef, useState, type ChangeEvent, type FormEvent, type KeyboardEvent } from 'react';
 import {
   SPECIAL_MENTIONS,
   insertMention,
@@ -13,6 +13,17 @@ interface Suggestion {
   insert: string;
 }
 
+/** Keyboard shortcut → the marker it wraps the selection in. */
+const SHORTCUTS: Record<string, string> = { b: '*', i: '_', e: '`' };
+
+/** Toolbar affordances for the same markers (strikethrough is button-only — no common shortcut). */
+const FORMAT_BUTTONS: Array<{ marker: string; label: string; title: string }> = [
+  { marker: '*', label: 'B', title: 'Bold (⌘B)' },
+  { marker: '_', label: 'I', title: 'Italic (⌘I)' },
+  { marker: '~', label: 'S', title: 'Strikethrough' },
+  { marker: '`', label: '‹›', title: 'Code (⌘E)' },
+];
+
 /**
  * The message input: draft, @mention autocomplete, and attachment staging. Shared by the main
  * Thread and the ThreadPane (which passes a parentInteractionId so a reply lands in the thread).
@@ -24,7 +35,7 @@ export function Composer({
   onSend,
   onTyping,
   parentInteractionId,
-  placeholder = 'Type a message… @ to mention',
+  placeholder = 'Type a message… @ to mention, *bold*',
 }: {
   members: Person[];
   canUpload: boolean;
@@ -40,6 +51,36 @@ export function Composer({
   const [uploading, setUploading] = useState(false);
   const [uploadingName, setUploadingName] = useState<string | null>(null);
   const fileRef = useRef<HTMLInputElement>(null);
+  const inputRef = useRef<HTMLTextAreaElement>(null);
+
+  // Grow with the content up to the CSS max-height, then scroll — a chat box, not a fixed field.
+  useEffect(() => {
+    const el = inputRef.current;
+    if (!el) return;
+    el.style.height = 'auto';
+    el.style.height = `${el.scrollHeight}px`;
+  }, [draft]);
+
+  /**
+   * Wrap the current selection in a marker (or, with nothing selected, drop in an empty pair and
+   * park the caret inside). Text stays plain — the marker characters ARE the format, so this never
+   * needs a rich-text model and the native spellchecker keeps working on the raw string.
+   */
+  function wrapSelection(marker: string): void {
+    const el = inputRef.current;
+    if (!el) return;
+    const start = el.selectionStart ?? draft.length;
+    const end = el.selectionEnd ?? start;
+    const selected = draft.slice(start, end);
+    const next = `${draft.slice(0, start)}${marker}${selected}${marker}${draft.slice(end)}`;
+    setDraft(next);
+    // Restore a sensible selection after React re-renders the value.
+    const caret = selected ? start + marker.length + selected.length + marker.length : start + marker.length;
+    requestAnimationFrame(() => {
+      el.focus();
+      el.setSelectionRange(selected ? start + marker.length : caret, selected ? caret - marker.length : caret);
+    });
+  }
 
   const query = trailingMentionQuery(draft);
   const suggestions = useMemo<Suggestion[]>(() => {
@@ -93,10 +134,26 @@ export function Composer({
     }
   }
 
-  function onKeyDown(e: KeyboardEvent<HTMLInputElement>): void {
-    if (showSuggest && e.key === 'Enter') {
+  function onKeyDown(e: KeyboardEvent<HTMLTextAreaElement>): void {
+    // Formatting shortcuts, matching the toolbar. Cmd on macOS, Ctrl elsewhere.
+    if (e.metaKey || e.ctrlKey) {
+      const marker = SHORTCUTS[e.key.toLowerCase()];
+      if (marker) {
+        e.preventDefault();
+        wrapSelection(marker);
+        return;
+      }
+    }
+    if (e.key !== 'Enter') return;
+    if (showSuggest) {
       e.preventDefault();
       pick(suggestions[0]!.insert);
+      return;
+    }
+    // Enter sends; Shift+Enter (and IME composition) inserts a newline.
+    if (!e.shiftKey && !e.nativeEvent.isComposing) {
+      e.preventDefault();
+      void submit();
     }
   }
 
@@ -125,6 +182,13 @@ export function Composer({
           </button>
         </div>
       ) : null}
+      <div className="miu-format-bar" role="group" aria-label="Formatting">
+        {FORMAT_BUTTONS.map((b) => (
+          <button key={b.marker} type="button" className="miu-format-btn" title={b.title} aria-label={b.title} onClick={() => wrapSelection(b.marker)}>
+            {b.label}
+          </button>
+        ))}
+      </div>
       <div className="miu-composer-row">
         {canUpload ? (
           <>
@@ -134,11 +198,18 @@ export function Composer({
             </button>
           </>
         ) : null}
-        <input
-          className="miu-input"
+        <textarea
+          ref={inputRef}
+          className="miu-input miu-textarea"
           value={draft}
           placeholder={placeholder}
           aria-label="Message"
+          rows={1}
+          // Native platform text services: the browser/OS supplies the red squiggle, the right-click
+          // suggestions and "Add to dictionary", and mobile keyboards add autocorrect. Nothing to ship.
+          spellCheck
+          autoCorrect="on"
+          autoCapitalize="sentences"
           onChange={(e) => {
             setDraft(e.target.value);
             onTyping?.();
diff --git a/packages/iios-messaging-ui/src/components/message-item.tsx b/packages/iios-messaging-ui/src/components/message-item.tsx
index 6b5e243..e151a14 100644
--- a/packages/iios-messaging-ui/src/components/message-item.tsx
+++ b/packages/iios-messaging-ui/src/components/message-item.tsx
@@ -1,5 +1,5 @@
 import { useRef, useState } from 'react';
-import { highlightMentions } from '../mentions';
+import { renderRichText } from '../rich-text';
 import { PopoverPortal } from './popover-portal';
 import type { Attachment } from '../types';
 import type { UiMessage } from '../hooks/use-messages';
@@ -65,7 +65,7 @@ export function MessageItem({
     <div className={`miu-msg${message.mine ? ' is-mine' : ''}${message.pending ? ' is-pending' : ''}`}>
       <div className="miu-bubble-row">
         <div className="miu-bubble">
-          {m.text ? highlightMentions(m.text, memberNames) : null}
+          {m.text ? renderRichText(m.text, memberNames) : null}
           {m.attachment ? <AttachmentView att={m.attachment} /> : null}
         </div>
         <time className="miu-msg-time" dateTime={m.at} title={Number.isNaN(+new Date(m.at)) ? '' : new Date(m.at).toLocaleString()}>
diff --git a/packages/iios-messaging-ui/src/index.ts b/packages/iios-messaging-ui/src/index.ts
index 28b0220..466ef9e 100644
--- a/packages/iios-messaging-ui/src/index.ts
+++ b/packages/iios-messaging-ui/src/index.ts
@@ -9,6 +9,8 @@ export { useMessages } from './hooks/use-messages';
 export { useChannels } from './hooks/use-channels';
 export { useMembers } from './hooks/use-members';
 export { isOwnMessage } from './types';
+// Message-body markup (bold/italic/strike/code/links + mentions) as a safe ReactNode tree.
+export { renderRichText, safeHref } from './rich-text';
 
 // Rendered UI. Pair with the './styles.css' export (or override the --miu-* tokens).
 export { Messenger } from './components/messenger';
diff --git a/packages/iios-messaging-ui/src/rich-text.test.tsx b/packages/iios-messaging-ui/src/rich-text.test.tsx
new file mode 100644
index 0000000..46d3802
--- /dev/null
+++ b/packages/iios-messaging-ui/src/rich-text.test.tsx
@@ -0,0 +1,77 @@
+import { describe, it, expect } from 'vitest';
+import { render, screen } from '@testing-library/react';
+import { renderRichText, safeHref } from './rich-text';
+
+function show(text: string, names: string[] = []) {
+  render(<div data-testid="out">{renderRichText(text, names)}</div>);
+  return screen.getByTestId('out');
+}
+
+describe('renderRichText', () => {
+  it('renders bold, italic and strikethrough', () => {
+    const el = show('*bold* _italic_ ~gone~');
+    expect(el.querySelector('strong')?.textContent).toBe('bold');
+    expect(el.querySelector('em')?.textContent).toBe('italic');
+    expect(el.querySelector('del')?.textContent).toBe('gone');
+  });
+
+  it('nests styles', () => {
+    const el = show('*bold with _italic_ inside*');
+    const strong = el.querySelector('strong');
+    expect(strong?.textContent).toBe('bold with italic inside');
+    expect(strong?.querySelector('em')?.textContent).toBe('italic');
+  });
+
+  it('leaves markup inside code completely literal', () => {
+    const el = show('use `*not bold*` here');
+    expect(el.querySelector('code')?.textContent).toBe('*not bold*');
+    expect(el.querySelector('strong')).toBeNull();
+  });
+
+  it('renders a fenced code block', () => {
+    const el = show('```\nconst a = 1;\n```');
+    expect(el.querySelector('pre.miu-code-block')?.textContent).toBe('const a = 1;\n');
+    expect(el.querySelector('code')).not.toBeNull();
+  });
+
+  it('does not treat arithmetic or a lone marker as formatting', () => {
+    const el = show('5 * 3 = 15 and a lone * plus snake_case_name');
+    expect(el.querySelector('strong')).toBeNull();
+    expect(el.querySelector('em')).toBeNull();
+    expect(el.textContent).toBe('5 * 3 = 15 and a lone * plus snake_case_name');
+  });
+
+  it('linkifies http(s) and www URLs without swallowing trailing punctuation', () => {
+    const el = show('see https://example.com/a?b=1, ok');
+    const a = el.querySelector('a');
+    expect(a?.getAttribute('href')).toBe('https://example.com/a?b=1');
+    expect(a?.textContent).toBe('https://example.com/a?b=1');
+    expect(a?.getAttribute('rel')).toContain('noopener');
+    expect(el.textContent).toContain(', ok');
+  });
+
+  it('never renders a javascript: URL as a link (XSS guard)', () => {
+    expect(safeHref('javascript:alert(1)')).toBeNull();
+    expect(safeHref('data:text/html,<script>')).toBeNull();
+    expect(safeHref('https://ok.example')).toBe('https://ok.example/');
+    // and it is not linkified in message text either
+    const el = show('javascript:alert(1)');
+    expect(el.querySelector('a')).toBeNull();
+  });
+
+  it('escapes nothing as HTML — angle brackets stay text', () => {
+    const el = show('<img src=x onerror=alert(1)>');
+    expect(el.querySelector('img')).toBeNull();
+    expect(el.textContent).toBe('<img src=x onerror=alert(1)>');
+  });
+
+  it('still highlights @mentions alongside formatting', () => {
+    const el = show('*hi* @Sofia Ramirez', ['Sofia Ramirez']);
+    expect(el.querySelector('strong')?.textContent).toBe('hi');
+    expect(el.querySelector('.miu-mention')?.textContent).toBe('@Sofia Ramirez');
+  });
+
+  it('returns plain text unchanged when there is no markup', () => {
+    expect(show('just a normal message').textContent).toBe('just a normal message');
+  });
+});
diff --git a/packages/iios-messaging-ui/src/rich-text.tsx b/packages/iios-messaging-ui/src/rich-text.tsx
new file mode 100644
index 0000000..f0a94bd
--- /dev/null
+++ b/packages/iios-messaging-ui/src/rich-text.tsx
@@ -0,0 +1,143 @@
+import type { ReactNode } from 'react';
+import { highlightMentions } from './mentions';
+
+/**
+ * WhatsApp-style lightweight markup for message bodies.
+ *
+ *   *bold*   _italic_   ~strike~   `code`   ```code block```   plus bare URLs
+ *
+ * Messages stay PLAIN TEXT on the wire — this only affects rendering, so nothing already stored
+ * breaks and a client without this build just shows the marker characters.
+ *
+ * Security: this returns a ReactNode tree and never touches dangerouslySetInnerHTML, so message
+ * text can never inject markup. The one genuinely dangerous surface is links, where an attacker
+ * could otherwise smuggle `javascript:` — {@link safeHref} allows only http/https/mailto.
+ *
+ * Precedence (deliberate): code is tokenized first and its contents are left completely alone, so
+ * `*not bold*` inside backticks stays literal. Everything else may nest (*bold with _italic_*).
+ */
+
+/** Only protocols that cannot execute script. Anything else renders as plain text, not a link. */
+export function safeHref(raw: string): string | null {
+  try {
+    const url = new URL(raw);
+    return ['http:', 'https:', 'mailto:'].includes(url.protocol) ? url.href : null;
+  } catch {
+    return null;
+  }
+}
+
+// A bare URL: stops before trailing punctuation so "see https://x.com." doesn't swallow the period.
+const URL_RE = /\bhttps?:\/\/[^\s<>()]+[^\s<>().,;:!?'"]|\bwww\.[^\s<>()]+[^\s<>().,;:!?'"]/g;
+
+interface Rule {
+  /** The wrapping marker, e.g. '*' for bold. */
+  marker: string;
+  tag: 'strong' | 'em' | 'del';
+}
+
+const RULES: Rule[] = [
+  { marker: '*', tag: 'strong' },
+  { marker: '_', tag: 'em' },
+  { marker: '~', tag: 'del' },
+];
+
+/** Escape a marker so it is literal inside a RegExp. */
+function esc(s: string): string {
+  return s.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
+}
+
+/**
+ * Find the first inline span (`*bold*`, `_italic_`, `~strike~`) in `text`.
+ *
+ * Two guards keep everyday prose from being mangled:
+ *   - the content must not start or end with whitespace, so "5 * 3 = 15" and a lone `*` are inert;
+ *   - the markers must sit on word boundaries, so `snake_case_name` is NOT italicised (the bug
+ *     every naive markdown renderer ships with).
+ */
+function firstSpan(text: string): { start: number; end: number; rule: Rule; inner: string } | null {
+  let best: { start: number; end: number; rule: Rule; inner: string } | null = null;
+  for (const rule of RULES) {
+    const m = esc(rule.marker);
+    // (lead)(marker)(inner)(marker) — `lead` keeps the boundary char out of the match itself.
+    const re = new RegExp(`(^|[^\\w${m}])${m}(?=\\S)([^${m}]*[^\\s${m}])${m}(?![\\w${m}])`);
+    const found = re.exec(text);
+    if (!found) continue;
+    const start = found.index + (found[1]?.length ?? 0);
+    if (best === null || start < best.start) {
+      best = { start, end: found.index + found[0].length, rule, inner: found[2] ?? '' };
+    }
+  }
+  return best;
+}
+
+/** Linkify + mention-highlight a run of text that carries no other markup. */
+function plain(text: string, memberNames: string[], keyed: () => string): ReactNode[] {
+  const out: ReactNode[] = [];
+  let last = 0;
+  let m: RegExpExecArray | null;
+  URL_RE.lastIndex = 0;
+  while ((m = URL_RE.exec(text)) !== null) {
+    if (m.index > last) out.push(...highlightMentions(text.slice(last, m.index), memberNames));
+    const raw = m[0];
+    const href = safeHref(raw.startsWith('www.') ? `https://${raw}` : raw);
+    out.push(
+      href ? (
+        <a key={keyed()} className="miu-link" href={href} target="_blank" rel="noopener noreferrer nofollow">
+          {raw}
+        </a>
+      ) : (
+        raw
+      ),
+    );
+    last = m.index + raw.length;
+  }
+  if (last < text.length) out.push(...highlightMentions(text.slice(last), memberNames));
+  return out;
+}
+
+/** Tokenize one segment that is known to contain no code, recursing so styles can nest. */
+function inline(text: string, memberNames: string[], keyed: () => string): ReactNode[] {
+  const span = firstSpan(text);
+  if (!span) return plain(text, memberNames, keyed);
+  const { start, end, rule, inner } = span;
+  const Tag = rule.tag;
+  return [
+    ...(start > 0 ? inline(text.slice(0, start), memberNames, keyed) : []),
+    <Tag key={keyed()}>{inline(inner, memberNames, keyed)}</Tag>,
+    ...(end < text.length ? inline(text.slice(end), memberNames, keyed) : []),
+  ];
+}
+
+/**
+ * Render message text as a safe ReactNode tree: code first (its contents stay literal), then
+ * nested bold/italic/strike, then links and @mentions.
+ */
+export function renderRichText(text: string, memberNames: string[] = []): ReactNode[] {
+  let n = 0;
+  const keyed = (): string => `rt${n++}`;
+  const out: ReactNode[] = [];
+  // ```block``` or `inline` — matched together so the longer fence wins.
+  const CODE_RE = /```([\s\S]+?)```|`([^`\n]+)`/g;
+  let last = 0;
+  let m: RegExpExecArray | null;
+  while ((m = CODE_RE.exec(text)) !== null) {
+    if (m.index > last) out.push(...inline(text.slice(last, m.index), memberNames, keyed));
+    if (m[1] !== undefined) {
+      out.push(
+        <pre key={keyed()} className="miu-code-block">
+          <code>{m[1].replace(/^\n/, '')}</code>
+        </pre>,
+      );
+    } else {
+      out.push(
+        <code key={keyed()} className="miu-code">
+          {m[2]}
+        </code>,
+      );
+    }
+    last = m.index + m[0].length;
+  }
+  if (last < text.length) out.push(...inline(text.slice(last), memberNames, keyed));
+  return out.length > 0 ? out : [text];
+}
diff --git a/packages/iios-messaging-ui/src/styles.css b/packages/iios-messaging-ui/src/styles.css
index fc6a0bc..2c8922e 100644
--- a/packages/iios-messaging-ui/src/styles.css
+++ b/packages/iios-messaging-ui/src/styles.css
@@ -515,6 +515,63 @@ button.miu-attach-dl:hover {
 .miu-input:focus {
   border-color: var(--miu-accent);
 }
+/* Chat box: one row by default, grows with content (JS sets height), then scrolls. */
+.miu-textarea {
+  resize: none;
+  min-height: 38px;
+  max-height: 160px;
+  overflow-y: auto;
+  line-height: 1.45;
+  font-family: inherit;
+}
+.miu-format-bar {
+  display: flex;
+  gap: 2px;
+  padding: 0 2px 4px;
+}
+.miu-format-btn {
+  min-width: 26px;
+  height: 24px;
+  padding: 0 6px;
+  border: none;
+  border-radius: 6px;
+  background: transparent;
+  color: var(--miu-muted);
+  font-size: 12px;
+  font-weight: 700;
+  cursor: pointer;
+}
+.miu-format-btn:hover {
+  background: var(--miu-panel-2);
+  color: var(--miu-text);
+}
+
+/* ── Rendered message formatting ── */
+.miu-code {
+  padding: 1px 5px;
+  border-radius: 5px;
+  background: var(--miu-panel-2);
+  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
+  font-size: 0.92em;
+}
+.miu-code-block {
+  margin: 6px 0 2px;
+  padding: 8px 10px;
+  border-radius: 8px;
+  background: var(--miu-panel-2);
+  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
+  font-size: 0.92em;
+  white-space: pre-wrap;
+  overflow-x: auto;
+}
+.miu-link {
+  color: var(--miu-accent);
+  text-decoration: underline;
+}
+.miu-msg.is-mine .miu-bubble .miu-link,
+.miu-msg.is-mine .miu-bubble .miu-code {
+  color: var(--miu-accent-text);
+}
 .miu-send {
   padding: 0 16px;
   border-radius: 10px;