diff --git a/extension/src/popup/styles.css b/extension/src/popup/styles.css
index 3f278fd..8e78353 100644
--- a/extension/src/popup/styles.css
+++ b/extension/src/popup/styles.css
@@ -1411,3 +1411,24 @@ textarea {
   color: var(--text-muted);
   font-variant-numeric: tabular-nums;
 }
+
+.totp-preview {
+  margin-top: 6px;
+  padding: 6px 10px;
+  border: 1px dashed var(--border-subtle);
+  border-radius: 3px;
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  font-variant-numeric: tabular-nums;
+  color: var(--text-muted);
+}
+.totp-code {
+  font-size: 14px;
+  font-weight: 600;
+  letter-spacing: 1px;
+  color: var(--accent);
+}
+.totp-countdown {
+  font-size: 11px;
+}
diff --git a/extension/src/shared/form-affordances/__tests__/totp-tools.test.ts b/extension/src/shared/form-affordances/__tests__/totp-tools.test.ts
new file mode 100644
index 0000000..0d0ff17
--- /dev/null
+++ b/extension/src/shared/form-affordances/__tests__/totp-tools.test.ts
@@ -0,0 +1,60 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { wireTotpPreview } from '../totp-tools';
+
+describe('wireTotpPreview', () => {
+  let form: HTMLElement;
+  let sendMessage: ReturnType<typeof vi.fn>;
+
+  beforeEach(() => {
+    form = document.createElement('div');
+    form.innerHTML = `
+      <input id="f-totp" type="text" value="" />
+      <div id="totp-preview-row" class="totp-preview" hidden>
+        <span class="totp-code">…</span>
+        <span class="totp-countdown">…</span>
+      </div>
+    `;
+    document.body.appendChild(form);
+    sendMessage = vi.fn();
+    vi.useFakeTimers();
+  });
+
+  it('shows preview when secret is valid base32', async () => {
+    sendMessage.mockResolvedValue({ ok: true, data: { code: '492837', expires_at: Math.floor(Date.now() / 1000) + 23 } });
+    const teardown = wireTotpPreview(form, { sendMessage });
+    const input = form.querySelector('#f-totp') as HTMLInputElement;
+    input.value = 'JBSWY3DPEHPK3PXP';
+    input.dispatchEvent(new Event('input'));
+    await vi.advanceTimersByTimeAsync(50);
+    const row = form.querySelector('#totp-preview-row') as HTMLElement;
+    expect(row.hidden).toBe(false);
+    expect(row.querySelector('.totp-code')?.textContent).toBe('492 837');
+    expect(row.querySelector('.totp-countdown')?.textContent).toMatch(/\d+s/);
+    teardown();
+  });
+
+  it('hides preview when secret is too short', async () => {
+    const teardown = wireTotpPreview(form, { sendMessage });
+    const input = form.querySelector('#f-totp') as HTMLInputElement;
+    input.value = 'TOOSHORT';
+    input.dispatchEvent(new Event('input'));
+    await vi.advanceTimersByTimeAsync(50);
+    const row = form.querySelector('#totp-preview-row') as HTMLElement;
+    expect(row.hidden).toBe(true);
+    expect(sendMessage).not.toHaveBeenCalled();
+    teardown();
+  });
+
+  it('teardown stops the interval', async () => {
+    sendMessage.mockResolvedValue({ ok: true, data: { code: '111111', expires_at: Math.floor(Date.now() / 1000) + 30 } });
+    const teardown = wireTotpPreview(form, { sendMessage });
+    const input = form.querySelector('#f-totp') as HTMLInputElement;
+    input.value = 'JBSWY3DPEHPK3PXP';
+    input.dispatchEvent(new Event('input'));
+    await vi.advanceTimersByTimeAsync(50);
+    const callsBefore = sendMessage.mock.calls.length;
+    teardown();
+    await vi.advanceTimersByTimeAsync(2000);
+    expect(sendMessage.mock.calls.length).toBe(callsBefore);
+  });
+});
diff --git a/extension/src/shared/form-affordances/totp-tools.ts b/extension/src/shared/form-affordances/totp-tools.ts
new file mode 100644
index 0000000..c1232ab
--- /dev/null
+++ b/extension/src/shared/form-affordances/totp-tools.ts
@@ -0,0 +1,53 @@
+export interface TotpPreviewOpts {
+  sendMessage: (msg: { type: 'preview_totp_from_secret'; secret_b32: string }) =>
+    Promise<{ ok: boolean; data?: { code: string; expires_at: number }; error?: string }>;
+}
+
+const VALID_B32 = /^[A-Z2-7]{16,}=*$/;
+
+export function wireTotpPreview(form: HTMLElement, opts: TotpPreviewOpts): () => void {
+  const input = form.querySelector<HTMLInputElement>('#f-totp');
+  const row = form.querySelector<HTMLElement>('#totp-preview-row');
+  if (!input || !row) return () => {};
+  const codeEl = row.querySelector<HTMLElement>('.totp-code');
+  const cdEl = row.querySelector<HTMLElement>('.totp-countdown');
+  if (!codeEl || !cdEl) return () => {};
+
+  let interval: ReturnType<typeof setInterval> | null = null;
+  let lastSecret = '';
+
+  const tick = async () => {
+    const cleaned = lastSecret.toUpperCase().replace(/\s+/g, '').replace(/=+$/, '');
+    if (!VALID_B32.test(cleaned)) {
+      row.hidden = true;
+      return;
+    }
+    const resp = await opts.sendMessage({ type: 'preview_totp_from_secret', secret_b32: cleaned });
+    if (!resp.ok || !resp.data) {
+      row.hidden = true;
+      return;
+    }
+    row.hidden = false;
+    // Format "492837" → "492 837" for legibility.
+    codeEl.textContent = resp.data.code.length === 6
+      ? `${resp.data.code.slice(0, 3)} ${resp.data.code.slice(3)}`
+      : resp.data.code;
+    const remaining = Math.max(0, resp.data.expires_at - Math.floor(Date.now() / 1000));
+    cdEl.textContent = `${remaining}s`;
+  };
+
+  const onInput = () => {
+    lastSecret = input.value;
+    void tick();
+  };
+  input.addEventListener('input', onInput);
+  if (interval === null) {
+    interval = setInterval(() => { void tick(); }, 1000);
+  }
+
+  return () => {
+    input.removeEventListener('input', onInput);
+    if (interval !== null) { clearInterval(interval); interval = null; }
+    row.hidden = true;
+  };
+}
diff --git a/extension/src/vault/vault.css b/extension/src/vault/vault.css
index b7099c8..6ae5155 100644
--- a/extension/src/vault/vault.css
+++ b/extension/src/vault/vault.css
@@ -1441,3 +1441,24 @@ textarea {
   color: var(--text-muted);
   font-variant-numeric: tabular-nums;
 }
+
+.totp-preview {
+  margin-top: 6px;
+  padding: 6px 10px;
+  border: 1px dashed var(--border-subtle);
+  border-radius: 3px;
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  font-variant-numeric: tabular-nums;
+  color: var(--text-muted);
+}
+.totp-code {
+  font-size: 14px;
+  font-weight: 600;
+  letter-spacing: 1px;
+  color: var(--accent);
+}
+.totp-countdown {
+  font-size: 11px;
+}