diff --git a/e2e/your-data.spec.ts b/e2e/your-data.spec.ts
new file mode 100644
index 000000000..379ae5e37
--- /dev/null
+++ b/e2e/your-data.spec.ts
@@ -0,0 +1,98 @@
+import fs from 'node:fs';
+import { test, expect } from '@playwright/test';
+import { api, ensureUser, hsReachable, loginUI, uniq } from './localHs';
+
+// [Gitea #114] Export / import "your data": a round trip through the file, the
+// merge summary, and the keep-mine / use-the-file's choice.
+const enc = encodeURIComponent;
+
+test.describe('your data (#114)', () => {
+  test.beforeAll(async () => {
+    test.skip(!(await hsReachable()), 'local homeserver not running');
+  });
+
+  test('export, change things, import merges with the chosen conflict rule', async ({ page }) => {
+    test.setTimeout(150_000);
+    const user = await ensureUser(uniq('yd'));
+    const put = (type: string, content: unknown) =>
+      api(
+        'PUT',
+        `/_matrix/client/v3/user/${enc(user.userId)}/account_data/${type}`,
+        user.token,
+        content,
+      );
+    const get = (type: string) =>
+      api<Record<string, unknown>>(
+        'GET',
+        `/_matrix/client/v3/user/${enc(user.userId)}/account_data/${type}`,
+        user.token,
+      );
+    const bm = (eventId: string) => ({ roomId: '!r:localhost', eventId, savedAt: 1 });
+    await put('io.lotus.bookmarks', { bookmarks: [bm('$one'), bm('$two')] });
+    await put('io.lotus.user_notes', { '@friend:localhost': 'met at the LAN party' });
+
+    await loginUI(page, user);
+    await page
+      .getByText('Connecting...')
+      .first()
+      .waitFor({ state: 'detached', timeout: 90_000 })
+      .catch(() => undefined);
+    const openGeneral = async () => {
+      await page.getByRole('button', { name: 'User Settings' }).click();
+      await page.getByRole('dialog').getByText('General', { exact: true }).first().click();
+      await page
+        .getByRole('dialog')
+        .getByText('Your data', { exact: true })
+        .scrollIntoViewIfNeeded();
+    };
+    await openGeneral();
+
+    // Export.
+    const [download] = await Promise.all([
+      page.waitForEvent('download'),
+      page.getByRole('dialog').getByRole('button', { name: 'Export', exact: true }).click(),
+    ]);
+    const path = await download.path();
+    const file = JSON.parse(fs.readFileSync(path!, 'utf8'));
+    expect(file.format).toBe('lotus-chat-data');
+    expect(file.accountData['io.lotus.bookmarks'].bookmarks).toHaveLength(2);
+    expect(file.local.settings).toBeTruthy();
+
+    // Lose a bookmark, change the note.
+    await put('io.lotus.bookmarks', { bookmarks: [bm('$one')] });
+    await put('io.lotus.user_notes', { '@friend:localhost': 'changed my mind' });
+    await page.waitForTimeout(3000); // let sync deliver the new account data
+
+    const importFile = async () => {
+      await page
+        .locator('input[type="file"][aria-label="Lotus Chat data file"]')
+        .setInputFiles(path!);
+      await expect(page.getByRole('region', { name: 'Import summary' })).toBeVisible();
+    };
+    await importFile();
+    const summary = page.getByRole('region', { name: 'Import summary' });
+    await expect(summary).toContainText('Bookmarks: 1 new');
+    await expect(summary).toContainText('Private notes about people: 1 differ');
+
+    // Keep mine: the bookmark comes back, the note stays as it is now.
+    await summary.getByRole('button', { name: 'Import', exact: true }).click();
+    await expect(page.getByText('Imported.')).toBeVisible({ timeout: 20_000 });
+    expect(((await get('io.lotus.bookmarks')).bookmarks as unknown[]).length).toBe(2);
+    expect((await get('io.lotus.user_notes'))['@friend:localhost']).toBe('changed my mind');
+
+    // Again, using the file's: the note goes back.
+    await page.waitForTimeout(2000);
+    await importFile();
+    await summary.getByText("Use the file's").click();
+    await summary.getByRole('button', { name: 'Import', exact: true }).click();
+    await expect(page.getByText('Imported.')).toBeVisible({ timeout: 20_000 });
+    expect((await get('io.lotus.user_notes'))['@friend:localhost']).toBe('met at the LAN party');
+
+    // Wrong files are refused with a plain message.
+    fs.writeFileSync(`${path}.bad`, '{"format":"something-else"}');
+    await page
+      .locator('input[type="file"][aria-label="Lotus Chat data file"]')
+      .setInputFiles(`${path}.bad`);
+    await expect(page.getByText("This isn't a Lotus Chat data file.")).toBeVisible();
+  });
+});
diff --git a/src/app/features/settings/general/General.tsx b/src/app/features/settings/general/General.tsx
index d1c9be22d..bc551da7c 100644
--- a/src/app/features/settings/general/General.tsx
+++ b/src/app/features/settings/general/General.tsx
@@ -61,6 +61,7 @@ import {
 } from '../../../utils/lotusDenoiseUtils';
 import { useSetting } from '../../../state/hooks/settings';
 import { useSettingsSyncActions } from '../../../hooks/useSettingsSync';
+import { YourDataSection } from './YourData';
 import {
   CallAudioBitrate,
   ChatBackground,
@@ -3007,6 +3008,7 @@ export function General({ requestClose }: GeneralProps) {
               <Privacy />
               <StorageUsage />
               <SettingsSyncSection />
+              <YourDataSection />
               <Calls />
               <DesktopSettings />
               <AppUpdates />
diff --git a/src/app/features/settings/general/YourData.tsx b/src/app/features/settings/general/YourData.tsx
new file mode 100644
index 000000000..1a9ea2e40
--- /dev/null
+++ b/src/app/features/settings/general/YourData.tsx
@@ -0,0 +1,285 @@
+import React, { useCallback, useRef, useState } from 'react';
+import { useAtom } from 'jotai';
+import { Method } from 'matrix-js-sdk';
+import { Box, Button, Text, color } from 'folds';
+import { SequenceCard } from '../../../components/sequence-card';
+import { SequenceCardStyle } from '../styles.css';
+import { SettingTile } from '../../../components/setting-tile';
+import { useMatrixClient } from '../../../hooks/useMatrixClient';
+import { Settings, settingsAtom } from '../../../state/settings';
+import {
+  buildExport,
+  EXPORT_ACCOUNT_DATA,
+  ExportFile,
+  ImportPlanItem,
+  mergeData,
+  parseExport,
+  planImport,
+} from '../../../utils/dataExport';
+import { invalidateDecorationCache } from '../../../hooks/useAvatarDecoration';
+
+const DECORATION_FIELD = 'io.lotus.avatar_decoration';
+
+type Current = {
+  accountData: Record<string, unknown>;
+  decoration: string | null;
+  localSettings: Record<string, unknown> | null;
+};
+
+/**
+ * [Gitea #114] "Your data": export the account's Lotus data (settings,
+ * bookmarks, notes, sections, ...) to a file and import it here or on another
+ * account. Import merges: new things are added; for things that differ the
+ * user picks "keep mine" (default) or "use the file's". Message history and
+ * encryption keys have their own exports.
+ */
+export function YourDataSection() {
+  const mx = useMatrixClient();
+  const userId = mx.getSafeUserId();
+  const [settings, setSettings] = useAtom(settingsAtom);
+  const fileInput = useRef<HTMLInputElement>(null);
+  const [pending, setPending] = useState<{ file: ExportFile; plan: ImportPlanItem[] }>();
+  const [preferFile, setPreferFile] = useState(false);
+  const [message, setMessage] = useState<{ tone: 'ok' | 'error'; text: string }>();
+  const [busy, setBusy] = useState(false);
+
+  const readCurrent = useCallback(async (): Promise<Current> => {
+    const accountData: Record<string, unknown> = {};
+    EXPORT_ACCOUNT_DATA.forEach(({ type }) => {
+      const c = mx.getAccountData(type as never)?.getContent();
+      if (c && Object.keys(c).length > 0) accountData[type] = c;
+    });
+    let decoration: string | null = null;
+    try {
+      const profile = await mx.http.authedRequest<Record<string, unknown>>(
+        Method.Get,
+        `/profile/${encodeURIComponent(userId)}`,
+      );
+      const v = profile[DECORATION_FIELD];
+      decoration = typeof v === 'string' && v ? v : null;
+    } catch {
+      /* no decoration */
+    }
+    return {
+      accountData,
+      decoration,
+      localSettings: settings as unknown as Record<string, unknown>,
+    };
+  }, [mx, userId, settings]);
+
+  const exportData = async () => {
+    setBusy(true);
+    setMessage(undefined);
+    try {
+      const cur = await readCurrent();
+      const file = buildExport({ userId, ...cur });
+      const blob = new Blob([JSON.stringify(file, null, 2)], { type: 'application/json' });
+      const url = URL.createObjectURL(blob);
+      const a = document.createElement('a');
+      a.href = url;
+      a.download = `lotus-chat-data-${userId.replace(/[^a-z0-9]+/gi, '-')}-${file.exportedAt.slice(0, 10)}.json`;
+      a.click();
+      URL.revokeObjectURL(url);
+      setMessage({ tone: 'ok', text: 'Exported. Keep the file somewhere safe.' });
+    } catch {
+      setMessage({ tone: 'error', text: "Couldn't export your data. Please try again." });
+    } finally {
+      setBusy(false);
+    }
+  };
+
+  const chooseFile = async (f: File | undefined) => {
+    if (!f) return;
+    setMessage(undefined);
+    const parsed = parseExport(await f.text());
+    if (!parsed.ok) {
+      setMessage({ tone: 'error', text: parsed.error });
+      return;
+    }
+    const plan = planImport(parsed.file, await readCurrent());
+    setPreferFile(false);
+    setPending({ file: parsed.file, plan });
+  };
+
+  const applyImport = async () => {
+    if (!pending) return;
+    setBusy(true);
+    try {
+      const cur = await readCurrent();
+      const { file } = pending;
+      await Object.entries(file.accountData).reduce<Promise<void>>(
+        async (prev, [type, incoming]) => {
+          await prev;
+          const r = mergeData(cur.accountData[type], incoming, preferFile);
+          if (r.added > 0 || (preferFile && r.conflicts > 0)) {
+            await mx.setAccountData(type as never, r.value as never);
+          }
+        },
+        Promise.resolve(),
+      );
+      const deco = file.profile.decoration;
+      if (deco && deco !== cur.decoration && (!cur.decoration || preferFile)) {
+        await mx.http.authedRequest(
+          Method.Put,
+          `/profile/${encodeURIComponent(userId)}/${DECORATION_FIELD}`,
+          undefined,
+          { [DECORATION_FIELD]: deco },
+        );
+        invalidateDecorationCache(userId);
+      }
+      if (file.local.settings) {
+        const r = mergeData(cur.localSettings ?? {}, file.local.settings, preferFile);
+        setSettings({ ...settings, ...(r.value as Partial<Settings>) });
+      }
+      setPending(undefined);
+      setMessage({ tone: 'ok', text: 'Imported.' });
+    } catch {
+      setMessage({ tone: 'error', text: "Couldn't finish the import. Nothing else was changed." });
+    } finally {
+      setBusy(false);
+    }
+  };
+
+  const totals = pending?.plan.reduce(
+    (t, p) => ({ added: t.added + p.added, conflicts: t.conflicts + p.conflicts }),
+    { added: 0, conflicts: 0 },
+  );
+
+  return (
+    <Box direction="Column" gap="100">
+      <Text size="L400">Your data</Text>
+      <SequenceCard
+        className={SequenceCardStyle}
+        variant="SurfaceVariant"
+        direction="Column"
+        gap="400"
+      >
+        <SettingTile
+          title="Export your data"
+          description="Settings, bookmarks, private notes, room sections and names, reminders, status presets, soundboard and emoji, as one file. Not your messages or encryption keys (they have their own exports)."
+          after={
+            <Button
+              size="300"
+              variant="Secondary"
+              fill="Soft"
+              radii="300"
+              outlined
+              disabled={busy}
+              onClick={exportData}
+            >
+              <Text size="B300">Export</Text>
+            </Button>
+          }
+        />
+        <SettingTile
+          title="Import data"
+          description="Load a Lotus Chat data file into this account. New items are added; you choose what happens to things that differ."
+          after={
+            <Button
+              size="300"
+              variant="Secondary"
+              fill="Soft"
+              radii="300"
+              outlined
+              disabled={busy}
+              onClick={() => fileInput.current?.click()}
+            >
+              <Text size="B300">Import…</Text>
+            </Button>
+          }
+        />
+        <input
+          ref={fileInput}
+          type="file"
+          accept="application/json,.json"
+          hidden
+          aria-label="Lotus Chat data file"
+          onChange={(e) => {
+            chooseFile(e.target.files?.[0]).catch(() => undefined);
+            e.target.value = '';
+          }}
+        />
+        {pending && totals && (
+          <Box direction="Column" gap="200" role="region" aria-label="Import summary">
+            {pending.file.userId && pending.file.userId !== userId && (
+              <Text size="T200">
+                This file is from <b>{pending.file.userId}</b>.
+              </Text>
+            )}
+            {pending.plan.map((p) => (
+              <Text key={p.key} size="T200">
+                {p.label}:{' '}
+                {p.added === 0 && p.conflicts === 0
+                  ? 'already up to date'
+                  : [p.added > 0 && `${p.added} new`, p.conflicts > 0 && `${p.conflicts} differ`]
+                      .filter(Boolean)
+                      .join(', ')}
+              </Text>
+            ))}
+            {totals.conflicts > 0 && (
+              <Box direction="Column" gap="100" role="radiogroup" aria-label="Things that differ">
+                <Text size="T200">
+                  <b>{totals.conflicts}</b>{' '}
+                  {totals.conflicts === 1 ? 'thing differs' : 'things differ'} from what&apos;s
+                  here:
+                </Text>
+                <label>
+                  <input
+                    type="radio"
+                    name="your-data-conflicts"
+                    checked={!preferFile}
+                    onChange={() => setPreferFile(false)}
+                  />{' '}
+                  <Text as="span" size="T200">
+                    Keep mine
+                  </Text>
+                </label>
+                <label>
+                  <input
+                    type="radio"
+                    name="your-data-conflicts"
+                    checked={preferFile}
+                    onChange={() => setPreferFile(true)}
+                  />{' '}
+                  <Text as="span" size="T200">
+                    Use the file&apos;s
+                  </Text>
+                </label>
+              </Box>
+            )}
+            <Box gap="200">
+              <Button
+                size="300"
+                variant="Primary"
+                radii="300"
+                disabled={busy || (totals.added === 0 && !(preferFile && totals.conflicts > 0))}
+                onClick={applyImport}
+              >
+                <Text size="B300">Import</Text>
+              </Button>
+              <Button
+                size="300"
+                variant="Secondary"
+                fill="Soft"
+                radii="300"
+                disabled={busy}
+                onClick={() => setPending(undefined)}
+              >
+                <Text size="B300">Cancel</Text>
+              </Button>
+            </Box>
+          </Box>
+        )}
+        {message && (
+          <Text
+            size="T200"
+            role="status"
+            style={{ color: message.tone === 'error' ? color.Critical.Main : undefined }}
+          >
+            {message.text}
+          </Text>
+        )}
+      </SequenceCard>
+    </Box>
+  );
+}
diff --git a/src/app/utils/dataExport.test.ts b/src/app/utils/dataExport.test.ts
new file mode 100644
index 000000000..6090bacdb
--- /dev/null
+++ b/src/app/utils/dataExport.test.ts
@@ -0,0 +1,76 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { buildExport, mergeData, parseExport, planImport } from './dataExport';
+
+const file = buildExport({
+  userId: '@a:hs',
+  accountData: {
+    'io.lotus.bookmarks': { bookmarks: [{ id: 'b1', note: 'x' }] },
+    'io.lotus.user_notes': { notes: { '@b:hs': 'met at LAN party' } },
+    'm.direct': { secret: true },
+    'io.lotus.settings': { theme: 'dark', fontSize: 16 },
+  },
+  decoration: 'halo',
+  localSettings: { callNoiseSuppression: 'ml' },
+  now: new Date('2026-10-25T00:00:00Z'),
+});
+
+test('[#114] export keeps only our own types', () => {
+  assert.equal(file.format, 'lotus-chat-data');
+  assert.equal(file.version, 1);
+  assert.deepEqual(Object.keys(file.accountData).sort(), [
+    'io.lotus.bookmarks',
+    'io.lotus.settings',
+    'io.lotus.user_notes',
+  ]);
+  assert.equal(file.profile.decoration, 'halo');
+});
+
+test('[#114] parse: round trip, wrong files, newer versions, foreign types', () => {
+  const r = parseExport(JSON.stringify(file));
+  assert.ok(r.ok);
+  assert.equal(parseExport('nope').ok, false);
+  assert.equal(parseExport('{"format":"other"}').ok, false);
+  const newer = parseExport(JSON.stringify({ ...file, version: 2 }));
+  assert.ok(!newer.ok && /newer Lotus Chat/.test(newer.error));
+  const sneaky = parseExport(
+    JSON.stringify({ ...file, accountData: { 'm.push_rules': {}, 'io.lotus.bookmarks': {} } }),
+  );
+  assert.ok(sneaky.ok);
+  assert.deepEqual(Object.keys(sneaky.file.accountData), ['io.lotus.bookmarks']);
+});
+
+test('[#114] merge: lists by id, maps by key, conflicts kept unless preferred', () => {
+  const mine = { bookmarks: [{ id: 'b1', note: 'mine' }, { id: 'b2' }] };
+  const theirs = { bookmarks: [{ id: 'b1', note: 'theirs' }, { id: 'b3' }] };
+  const keep = mergeData(mine, theirs);
+  assert.equal(keep.added, 1);
+  assert.equal(keep.conflicts, 1);
+  assert.deepEqual(keep.value, {
+    bookmarks: [{ id: 'b1', note: 'mine' }, { id: 'b2' }, { id: 'b3' }],
+  });
+  const take = mergeData(mine, theirs, true);
+  assert.deepEqual((take.value as typeof mine).bookmarks[0], { id: 'b1', note: 'theirs' });
+
+  const notes = mergeData({ a: 1, b: 2 }, { b: 3, c: 4 });
+  assert.deepEqual(notes, { value: { a: 1, b: 2, c: 4 }, added: 1, conflicts: 1 });
+  assert.deepEqual(mergeData(undefined, { x: 1 }), { value: { x: 1 }, added: 1, conflicts: 0 });
+  assert.deepEqual(mergeData(['a'], ['a', 'b']).value, ['a', 'b']);
+});
+
+test('[#114] plan summarises per category', () => {
+  const plan = planImport(file, {
+    accountData: { 'io.lotus.settings': { theme: 'light' } },
+    decoration: null,
+    localSettings: { callNoiseSuppression: 'ml' },
+  });
+  const by = Object.fromEntries(plan.map((p) => [p.key, p]));
+  assert.deepEqual(
+    [by['io.lotus.settings'].added, by['io.lotus.settings'].conflicts],
+    [1, 1],
+    'fontSize new, theme differs',
+  );
+  assert.equal(by['io.lotus.bookmarks'].added, 1);
+  assert.equal(by['profile.decoration'].added, 1);
+  assert.deepEqual([by['local.settings'].added, by['local.settings'].conflicts], [0, 0]);
+});
diff --git a/src/app/utils/dataExport.ts b/src/app/utils/dataExport.ts
new file mode 100644
index 000000000..629f968ee
--- /dev/null
+++ b/src/app/utils/dataExport.ts
@@ -0,0 +1,219 @@
+/**
+ * [Gitea #114] Export / import "your data": the Lotus-side personal data of
+ * an account (not message history, not encryption keys: those have their own
+ * exports, and keys are secret). One JSON file:
+ *
+ *   { format: 'lotus-chat-data', version: 1, exportedAt, userId,
+ *     accountData: { [type]: content }, profile: { decoration }, local: { settings } }
+ *
+ * Import MERGES: anything missing here is added; a value that differs is a
+ * conflict, kept as it is unless the user chooses the file's. Pure helpers.
+ */
+
+export const EXPORT_FORMAT = 'lotus-chat-data';
+export const EXPORT_VERSION = 1;
+
+/** The account-data types that are the user's own Lotus data, with labels. */
+export const EXPORT_ACCOUNT_DATA: { type: string; label: string }[] = [
+  { type: 'io.lotus.settings', label: 'Synced settings' },
+  { type: 'io.lotus.bookmarks', label: 'Bookmarks' },
+  { type: 'io.lotus.user_notes', label: 'Private notes about people' },
+  { type: 'io.lotus.room_names', label: 'Your names for rooms' },
+  { type: 'in.cinny.spaces', label: 'Room sections and sidebar' },
+  { type: 'io.lotus.reminders', label: 'Reminders' },
+  { type: 'io.lotus.status_presets', label: 'Status presets' },
+  { type: 'io.lotus.thread_notifications', label: 'Thread notification settings' },
+  { type: 'io.lotus.mute_timers', label: 'Timed mutes' },
+  { type: 'io.lotus.soundboard', label: 'Soundboard (clips stay on the server)' },
+  { type: 'io.lotus.soundboard_rooms', label: 'Soundboards enabled everywhere' },
+  { type: 'im.ponies.user_emotes', label: 'Your emoji and stickers' },
+  { type: 'im.ponies.emote_rooms', label: 'Emoji packs enabled everywhere' },
+];
+
+export type ExportFile = {
+  format: typeof EXPORT_FORMAT;
+  version: number;
+  exportedAt: string;
+  userId: string;
+  accountData: Record<string, unknown>;
+  profile: { decoration: string | null };
+  local: { settings: Record<string, unknown> | null };
+};
+
+export const buildExport = (input: {
+  userId: string;
+  accountData: Record<string, unknown>;
+  decoration: string | null;
+  localSettings: Record<string, unknown> | null;
+  now?: Date;
+}): ExportFile => {
+  const accountData: Record<string, unknown> = {};
+  EXPORT_ACCOUNT_DATA.forEach(({ type }) => {
+    const c = input.accountData[type];
+    if (c !== undefined && c !== null) accountData[type] = c;
+  });
+  return {
+    format: EXPORT_FORMAT,
+    version: EXPORT_VERSION,
+    exportedAt: (input.now ?? new Date()).toISOString(),
+    userId: input.userId,
+    accountData,
+    profile: { decoration: input.decoration },
+    local: { settings: input.localSettings },
+  };
+};
+
+const isObject = (v: unknown): v is Record<string, unknown> =>
+  !!v && typeof v === 'object' && !Array.isArray(v);
+
+export type ParseResult = { ok: true; file: ExportFile } | { ok: false; error: string };
+
+/** Validate an imported file; older versions would be migrated here. */
+export const parseExport = (text: string): ParseResult => {
+  let v: unknown;
+  try {
+    v = JSON.parse(text);
+  } catch {
+    return { ok: false, error: "This isn't a Lotus Chat data file (it isn't valid JSON)." };
+  }
+  if (!isObject(v) || v.format !== EXPORT_FORMAT)
+    return { ok: false, error: "This isn't a Lotus Chat data file." };
+  if (typeof v.version !== 'number' || v.version < 1)
+    return { ok: false, error: 'This data file is damaged (no version).' };
+  if (v.version > EXPORT_VERSION)
+    return {
+      ok: false,
+      error: 'This file was made by a newer Lotus Chat. Update the app, then import it again.',
+    };
+  const accountData = isObject(v.accountData) ? v.accountData : {};
+  const known = new Set(EXPORT_ACCOUNT_DATA.map((t) => t.type));
+  const filtered: Record<string, unknown> = {};
+  Object.entries(accountData).forEach(([type, content]) => {
+    // Only our own types: a file can't be used to write arbitrary account data.
+    if (known.has(type) && content !== null && content !== undefined) filtered[type] = content;
+  });
+  const profile = isObject(v.profile) ? v.profile : {};
+  const local = isObject(v.local) ? v.local : {};
+  return {
+    ok: true,
+    file: {
+      format: EXPORT_FORMAT,
+      version: v.version,
+      exportedAt: typeof v.exportedAt === 'string' ? v.exportedAt : '',
+      userId: typeof v.userId === 'string' ? v.userId : '',
+      accountData: filtered,
+      profile: {
+        decoration: typeof profile.decoration === 'string' ? profile.decoration : null,
+      },
+      local: { settings: isObject(local.settings) ? local.settings : null },
+    },
+  };
+};
+
+const same = (a: unknown, b: unknown): boolean => JSON.stringify(a) === JSON.stringify(b);
+
+const itemKey = (v: unknown): string => {
+  if (isObject(v)) {
+    const id = v.id ?? v.eventId ?? v.event_id ?? v.key ?? v.roomId ?? v.room_id ?? v.mxc;
+    if (typeof id === 'string' || typeof id === 'number') return `id:${String(id)}`;
+  }
+  return `json:${JSON.stringify(v)}`;
+};
+
+export type MergeResult = { value: unknown; added: number; conflicts: number };
+
+/**
+ * Pure: merge `incoming` into `current`. Lists: add items that are missing
+ * (matched by id, else by content). Objects: add missing keys, recurse into
+ * shared ones. A differing leaf is a conflict: `preferIncoming` decides.
+ */
+export const mergeData = (
+  current: unknown,
+  incoming: unknown,
+  preferIncoming = false,
+): MergeResult => {
+  if (current === undefined || current === null) {
+    return { value: incoming, added: incoming === undefined ? 0 : 1, conflicts: 0 };
+  }
+  if (Array.isArray(current) && Array.isArray(incoming)) {
+    const have = new Map(current.map((v, i) => [itemKey(v), i]));
+    const out = [...current];
+    let added = 0;
+    let conflicts = 0;
+    incoming.forEach((item) => {
+      const k = itemKey(item);
+      const at = have.get(k);
+      if (at === undefined) {
+        out.push(item);
+        have.set(k, out.length - 1);
+        added += 1;
+      } else if (!same(out[at], item)) {
+        conflicts += 1;
+        if (preferIncoming) out[at] = item;
+      }
+    });
+    return { value: out, added, conflicts };
+  }
+  if (isObject(current) && isObject(incoming)) {
+    const out: Record<string, unknown> = { ...current };
+    let added = 0;
+    let conflicts = 0;
+    Object.entries(incoming).forEach(([k, v]) => {
+      if (!(k in current)) {
+        out[k] = v;
+        added += 1;
+        return;
+      }
+      const r = mergeData(current[k], v, preferIncoming);
+      out[k] = r.value;
+      added += r.added;
+      conflicts += r.conflicts;
+    });
+    return { value: out, added, conflicts };
+  }
+  if (same(current, incoming)) return { value: current, added: 0, conflicts: 0 };
+  return { value: preferIncoming ? incoming : current, added: 0, conflicts: 1 };
+};
+
+export type ImportPlanItem = {
+  key: string;
+  label: string;
+  added: number;
+  conflicts: number;
+};
+
+/** What importing `file` into the current data would change, per category. */
+export const planImport = (
+  file: ExportFile,
+  current: {
+    accountData: Record<string, unknown>;
+    decoration: string | null;
+    localSettings: Record<string, unknown> | null;
+  },
+): ImportPlanItem[] => {
+  const items: ImportPlanItem[] = [];
+  EXPORT_ACCOUNT_DATA.forEach(({ type, label }) => {
+    if (!(type in file.accountData)) return;
+    const r = mergeData(current.accountData[type], file.accountData[type]);
+    items.push({ key: type, label, added: r.added, conflicts: r.conflicts });
+  });
+  if (file.profile.decoration !== null) {
+    const differs = current.decoration !== file.profile.decoration;
+    items.push({
+      key: 'profile.decoration',
+      label: 'Avatar decoration',
+      added: !current.decoration && differs ? 1 : 0,
+      conflicts: current.decoration && differs ? 1 : 0,
+    });
+  }
+  if (file.local.settings) {
+    const r = mergeData(current.localSettings ?? {}, file.local.settings);
+    items.push({
+      key: 'local.settings',
+      label: "This device's settings",
+      added: r.added,
+      conflicts: r.conflicts,
+    });
+  }
+  return items;
+};