diff --git a/services/platform-service/src/lib/cosmos-init.ts b/services/platform-service/src/lib/cosmos-init.ts
index d1f1bb5f..aad7d158 100644
--- a/services/platform-service/src/lib/cosmos-init.ts
+++ b/services/platform-service/src/lib/cosmos-init.ts
@@ -5,6 +5,7 @@ import { config } from './config.js';
 const CONTAINER_DEFS: Record<string, ContainerConfig> = {
   products: { partitionKeyPath: '/id' },
   users: { partitionKeyPath: '/id' },
+  settings: { partitionKeyPath: '/userId' },
   devices: { partitionKeyPath: '/userId' },
   notification_prefs: { partitionKeyPath: '/userId' },
   audit_log: { partitionKeyPath: '/category', defaultTtl: 90 * 86400 },
diff --git a/services/platform-service/src/modules/settings/repository.ts b/services/platform-service/src/modules/settings/repository.ts
new file mode 100644
index 00000000..ea7ba268
--- /dev/null
+++ b/services/platform-service/src/modules/settings/repository.ts
@@ -0,0 +1,32 @@
+/**
+ * User settings repository — Cosmos DB CRUD for settings + device overrides.
+ */
+
+import { getContainer } from '../../lib/cosmos.js';
+import type { UserSettingsDoc } from './types.js';
+
+function container() {
+  return getContainer('settings');
+}
+
+export function getSettingsId(productId: string, userId: string): string {
+  return `set_${productId}_${userId}`;
+}
+
+export async function getByUserId(
+  userId: string,
+  productId: string
+): Promise<UserSettingsDoc | null> {
+  const id = getSettingsId(productId, userId);
+  try {
+    const { resource } = await container().item(id, userId).read<UserSettingsDoc>();
+    return resource ?? null;
+  } catch {
+    return null;
+  }
+}
+
+export async function upsert(doc: UserSettingsDoc): Promise<UserSettingsDoc> {
+  const { resource } = await container().items.upsert<UserSettingsDoc>(doc);
+  return resource!;
+}
diff --git a/services/platform-service/src/modules/settings/routes.ts b/services/platform-service/src/modules/settings/routes.ts
new file mode 100644
index 00000000..afb4f5fb
--- /dev/null
+++ b/services/platform-service/src/modules/settings/routes.ts
@@ -0,0 +1,126 @@
+/**
+ * User settings REST endpoints.
+ *
+ * GET    /settings                   — get user settings
+ * PUT    /settings                   — merge global settings
+ * GET    /settings/device/:deviceId  — get resolved settings for a device
+ * PUT    /settings/device/:deviceId  — set per-device overrides
+ * DELETE /settings/device/:deviceId  — clear per-device overrides
+ */
+
+import type { FastifyInstance, FastifyRequest } from 'fastify';
+import { getRequestProductId } from '../../lib/request-context.js';
+import { BadRequestError, UnauthorizedError } from '../../lib/errors.js';
+import * as repo from './repository.js';
+import { UpdateSettingsSchema, SetDeviceOverridesSchema, type UserSettingsDoc } from './types.js';
+
+function getRequestUserId(req: FastifyRequest): string {
+  const userId = req.jwtPayload?.sub;
+  if (!userId) throw new UnauthorizedError('Authentication required');
+  return userId;
+}
+
+function buildDefaultDoc(productId: string, userId: string): UserSettingsDoc {
+  const now = new Date().toISOString();
+  return {
+    id: repo.getSettingsId(productId, userId),
+    productId,
+    userId,
+    settings: {},
+    deviceOverrides: {},
+    createdAt: now,
+    updatedAt: now,
+  };
+}
+
+export async function settingsRoutes(app: FastifyInstance) {
+  app.get('/settings', async req => {
+    const productId = getRequestProductId(req);
+    const userId = getRequestUserId(req);
+
+    const existing = await repo.getByUserId(userId, productId);
+    return existing ?? buildDefaultDoc(productId, userId);
+  });
+
+  app.put('/settings', async req => {
+    const parsed = UpdateSettingsSchema.safeParse(req.body);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+
+    const productId = getRequestProductId(req);
+    const userId = getRequestUserId(req);
+    const existing = await repo.getByUserId(userId, productId);
+    const now = new Date().toISOString();
+
+    const doc: UserSettingsDoc = {
+      ...(existing ?? buildDefaultDoc(productId, userId)),
+      settings: { ...(existing?.settings ?? {}), ...parsed.data.settings },
+      updatedAt: now,
+    };
+
+    return repo.upsert(doc);
+  });
+
+  app.get('/settings/device/:deviceId', async req => {
+    const { deviceId } = req.params as { deviceId: string };
+    const productId = getRequestProductId(req);
+    const userId = getRequestUserId(req);
+
+    const existing = await repo.getByUserId(userId, productId);
+    const doc = existing ?? buildDefaultDoc(productId, userId);
+    const overrides = doc.deviceOverrides[deviceId] ?? {};
+
+    return {
+      deviceId,
+      settings: { ...doc.settings, ...overrides },
+      hasOverrides: Object.keys(overrides).length > 0,
+    };
+  });
+
+  app.put('/settings/device/:deviceId', async req => {
+    const { deviceId } = req.params as { deviceId: string };
+    const parsed = SetDeviceOverridesSchema.safeParse(req.body);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+
+    const productId = getRequestProductId(req);
+    const userId = getRequestUserId(req);
+    const existing = await repo.getByUserId(userId, productId);
+    const now = new Date().toISOString();
+
+    const doc: UserSettingsDoc = {
+      ...(existing ?? buildDefaultDoc(productId, userId)),
+      deviceOverrides: {
+        ...(existing?.deviceOverrides ?? {}),
+        [deviceId]: parsed.data.overrides,
+      },
+      updatedAt: now,
+    };
+
+    await repo.upsert(doc);
+    return { deviceId, overrides: doc.deviceOverrides[deviceId] };
+  });
+
+  app.delete('/settings/device/:deviceId', async req => {
+    const { deviceId } = req.params as { deviceId: string };
+    const productId = getRequestProductId(req);
+    const userId = getRequestUserId(req);
+    const existing = await repo.getByUserId(userId, productId);
+
+    if (!existing) return { success: true, deviceId };
+
+    const now = new Date().toISOString();
+    const nextOverrides = { ...existing.deviceOverrides };
+    delete nextOverrides[deviceId];
+
+    await repo.upsert({
+      ...existing,
+      deviceOverrides: nextOverrides,
+      updatedAt: now,
+    });
+
+    return { success: true, deviceId };
+  });
+}
diff --git a/services/platform-service/src/modules/settings/settings.test.ts b/services/platform-service/src/modules/settings/settings.test.ts
new file mode 100644
index 00000000..d23e74f6
--- /dev/null
+++ b/services/platform-service/src/modules/settings/settings.test.ts
@@ -0,0 +1,49 @@
+/**
+ * Unit tests for settings module — types + validation.
+ */
+
+import { describe, it, expect } from 'vitest';
+import { SetDeviceOverridesSchema, UpdateSettingsSchema } from './types.js';
+
+describe('UpdateSettingsSchema', () => {
+  it('accepts generic settings payload', () => {
+    const result = UpdateSettingsSchema.safeParse({
+      settings: {
+        hotkey: 'fn',
+        language: 'en-US',
+        cleanup_enabled: true,
+        custom_vocabulary: ['alpha', 'beta'],
+      },
+    });
+    expect(result.success).toBe(true);
+  });
+
+  it('rejects missing settings object', () => {
+    const result = UpdateSettingsSchema.safeParse({});
+    expect(result.success).toBe(false);
+  });
+});
+
+describe('SetDeviceOverridesSchema', () => {
+  it('accepts per-device overrides payload', () => {
+    const result = SetDeviceOverridesSchema.safeParse({
+      overrides: {
+        language: 'en-GB',
+        sound_enabled: false,
+      },
+    });
+    expect(result.success).toBe(true);
+  });
+
+  it('rejects missing overrides object', () => {
+    const result = SetDeviceOverridesSchema.safeParse({});
+    expect(result.success).toBe(false);
+  });
+});
+
+describe('settingsRoutes export', () => {
+  it('exports settingsRoutes function', async () => {
+    const mod = await import('./routes.js');
+    expect(typeof mod.settingsRoutes).toBe('function');
+  });
+});
diff --git a/services/platform-service/src/modules/settings/types.ts b/services/platform-service/src/modules/settings/types.ts
new file mode 100644
index 00000000..410ee4dc
--- /dev/null
+++ b/services/platform-service/src/modules/settings/types.ts
@@ -0,0 +1,26 @@
+/**
+ * User settings types — product-scoped settings with per-device overrides.
+ */
+
+import { z } from 'zod';
+
+export interface UserSettingsDoc {
+  id: string;
+  productId: string;
+  userId: string;
+  settings: Record<string, unknown>;
+  deviceOverrides: Record<string, Record<string, unknown>>;
+  createdAt: string;
+  updatedAt: string;
+}
+
+export const UpdateSettingsSchema = z.object({
+  settings: z.record(z.unknown()),
+});
+
+export const SetDeviceOverridesSchema = z.object({
+  overrides: z.record(z.unknown()),
+});
+
+export type UpdateSettingsInput = z.infer<typeof UpdateSettingsSchema>;
+export type SetDeviceOverridesInput = z.infer<typeof SetDeviceOverridesSchema>;
diff --git a/services/platform-service/src/server.ts b/services/platform-service/src/server.ts
index 75daebe8..0264519c 100644
--- a/services/platform-service/src/server.ts
+++ b/services/platform-service/src/server.ts
@@ -37,6 +37,7 @@ import { usageRoutes } from './modules/usage/routes.js';
 import { planRoutes } from './modules/plans/routes.js';
 import { licenseRoutes } from './modules/licenses/routes.js';
 import { stripeRoutes } from './modules/stripe/routes.js';
+import { settingsRoutes } from './modules/settings/routes.js';
 import { itemRoutes } from './modules/items/routes.js';
 import { commentRoutes } from './modules/comments/routes.js';
 import { voteRoutes } from './modules/votes/routes.js';
@@ -98,6 +99,8 @@ await app.register(planRoutes, { prefix: '/api' });
 await app.register(licenseRoutes, { prefix: '/api' });
 // Stripe routes outside billing scope (webhook has its own signature verification)
 await app.register(stripeRoutes, { prefix: '/api' });
+// Settings module (user-level global settings + per-device overrides)
+await app.register(settingsRoutes, { prefix: '/api' });
 // Tracker modules (merged from tracker-service)
 await app.register(itemRoutes, { prefix: '/api' });
 await app.register(commentRoutes, { prefix: '/api' });