diff --git a/AGENTS.md b/AGENTS.md
index 056c106..f3f2631 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -18,6 +18,7 @@ Self-hosted journaling app where users capture events throughout the day and AI
   /src
     index.ts               # Main API routes, journal generation logic
     /services/ai           # AI provider implementations (Groq, OpenAI, Anthropic, Ollama, LMStudio)
+    /__tests__/            # API unit tests (Bun test)
 
 /frontend
   /src
@@ -191,6 +192,13 @@ bunx prisma migrate dev --name migration_name
 docker compose build && docker compose up -d
 ```
 
+### Running Tests
+```bash
+cd backend
+bun run test:server
+```
+Tests require the server running. The test script starts the server, runs tests, then stops it.
+
 ## Version History
 - 0.1.0: Automatic geolocation capture, Starlight documentation site
 - 0.0.6: Automatic geolocation capture on event creation, reverse geocoding to place names
diff --git a/backend/bunfig.toml b/backend/bunfig.toml
new file mode 100644
index 0000000..c05df21
--- /dev/null
+++ b/backend/bunfig.toml
@@ -0,0 +1,2 @@
+[test]
+preload = ["./src/__tests__/helpers.ts"]
diff --git a/backend/package.json b/backend/package.json
index 12ffa80..403635c 100644
--- a/backend/package.json
+++ b/backend/package.json
@@ -9,7 +9,10 @@
     "db:generate": "prisma generate",
     "db:push": "prisma db push",
     "db:migrate": "prisma migrate dev",
-    "db:studio": "prisma studio"
+    "db:studio": "prisma studio",
+    "test": "bun test",
+    "test:watch": "bun test --watch",
+    "test:server": "bun run src/index.ts & sleep 2 && bun test && kill $!"
   },
   "dependencies": {
     "@prisma/client": "^5.22.0",
diff --git a/backend/src/__tests__/auth.test.ts b/backend/src/__tests__/auth.test.ts
new file mode 100644
index 0000000..3801e88
--- /dev/null
+++ b/backend/src/__tests__/auth.test.ts
@@ -0,0 +1,57 @@
+import { describe, it, expect, beforeAll } from 'bun:test';
+import { createTestUser, createEvent } from './helpers';
+
+describe('Auth API', () => {
+  it('should register a new user', async () => {
+    const res = await fetch('http://localhost:3000/api/v1/auth/register', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({
+        email: `newuser_${Date.now()}@test.com`,
+        password: 'password123',
+      }),
+    });
+    const json = await res.json();
+    expect(res.status).toBe(201);
+    expect(json.data).toBeDefined();
+    expect(json.data.apiKey).toBeDefined();
+  });
+
+  it('should reject duplicate email', async () => {
+    const email = `duplicate_${Date.now()}@test.com`;
+    await createTestUser(email, 'password123');
+    
+    const res = await fetch('http://localhost:3000/api/v1/auth/register', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ email, password: 'password123' }),
+    });
+    expect(res.status).toBe(400);
+  });
+
+  it('should login with valid credentials', async () => {
+    const email = `login_${Date.now()}@test.com`;
+    await createTestUser(email, 'mypassword');
+    
+    const res = await fetch('http://localhost:3000/api/v1/auth/login', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ email, password: 'mypassword' }),
+    });
+    const json = await res.json();
+    expect(res.status).toBe(200);
+    expect(json.data.token).toBeDefined();
+  });
+
+  it('should reject invalid password', async () => {
+    const email = `invalid_${Date.now()}@test.com`;
+    await createTestUser(email, 'correctpassword');
+    
+    const res = await fetch('http://localhost:3000/api/v1/auth/login', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ email, password: 'wrongpassword' }),
+    });
+    expect(res.status).toBe(401);
+  });
+});
diff --git a/backend/src/__tests__/days.test.ts b/backend/src/__tests__/days.test.ts
new file mode 100644
index 0000000..b4a8ac7
--- /dev/null
+++ b/backend/src/__tests__/days.test.ts
@@ -0,0 +1,45 @@
+import { describe, it, expect, beforeEach } from 'bun:test';
+import { getApiKey, createEvent } from './helpers';
+
+describe('Days API', () => {
+  let apiKey: string;
+
+  beforeEach(async () => {
+    apiKey = await getApiKey();
+  });
+
+  it('should list days with events', async () => {
+    await createEvent(apiKey, '2026-03-25', 'text', 'Day listing test');
+    
+    const res = await fetch('http://localhost:3000/api/v1/days', {
+      headers: { 'Authorization': `Bearer ${apiKey}` },
+    });
+    const json = await res.json();
+    expect(json.data).toBeDefined();
+    expect(Array.isArray(json.data.days)).toBe(true);
+  });
+
+  it('should get day with events and journal', async () => {
+    const date = '2026-03-26';
+    await createEvent(apiKey, date, 'text', 'Day details test');
+    
+    const res = await fetch(`http://localhost:3000/api/v1/days/${date}`, {
+      headers: { 'Authorization': `Bearer ${apiKey}` },
+    });
+    const json = await res.json();
+    expect(json.data).toBeDefined();
+    expect(json.data.date).toBe(date);
+    expect(json.data.events).toBeDefined();
+    expect(Array.isArray(json.data.events)).toBe(true);
+    expect(json.data.events.length).toBeGreaterThan(0);
+  });
+
+  it('should return empty events for day with no events', async () => {
+    const res = await fetch('http://localhost:3000/api/v1/days/2099-12-31', {
+      headers: { 'Authorization': `Bearer ${apiKey}` },
+    });
+    const json = await res.json();
+    expect(json.data.events.length).toBe(0);
+    expect(json.data.journal).toBeNull();
+  });
+});
diff --git a/backend/src/__tests__/events.test.ts b/backend/src/__tests__/events.test.ts
new file mode 100644
index 0000000..e94636a
--- /dev/null
+++ b/backend/src/__tests__/events.test.ts
@@ -0,0 +1,98 @@
+import { describe, it, expect, beforeEach } from 'bun:test';
+import { getApiKey, createEvent } from './helpers';
+
+describe('Events API', () => {
+  let apiKey: string;
+  const testDate = '2026-03-27';
+
+  beforeEach(async () => {
+    apiKey = await getApiKey();
+  });
+
+  it('should create an event', async () => {
+    const res = await createEvent(apiKey, testDate, 'text', 'Test event content');
+    expect(res.data).toBeDefined();
+    expect(res.data.content).toBe('Test event content');
+    expect(res.data.type).toBe('text');
+    expect(res.data.date).toBe(testDate);
+  });
+
+  it('should create event with location', async () => {
+    const res = await fetch('http://localhost:3000/api/v1/events', {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json',
+        'Authorization': `Bearer ${apiKey}`,
+      },
+      body: JSON.stringify({
+        date: testDate,
+        type: 'text',
+        content: 'Event with location',
+        latitude: 40.7128,
+        longitude: -74.006,
+        placeName: 'New York, NY',
+      }),
+    });
+    const json = await res.json();
+    expect(json.data.latitude).toBe(40.7128);
+    expect(json.data.longitude).toBe(-74.006);
+    expect(json.data.placeName).toBe('New York, NY');
+  });
+
+  it('should reject event without content', async () => {
+    const res = await fetch('http://localhost:3000/api/v1/events', {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json',
+        'Authorization': `Bearer ${apiKey}`,
+      },
+      body: JSON.stringify({
+        date: testDate,
+        type: 'text',
+        content: '',
+      }),
+    });
+    expect(res.status).toBe(400);
+  });
+
+  it('should reject event with invalid type', async () => {
+    const res = await fetch('http://localhost:3000/api/v1/events', {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json',
+        'Authorization': `Bearer ${apiKey}`,
+      },
+      body: JSON.stringify({
+        date: testDate,
+        type: 'invalid',
+        content: 'Test',
+      }),
+    });
+    expect(res.status).toBe(400);
+  });
+
+  it('should get day events', async () => {
+    await createEvent(apiKey, testDate, 'text', 'Event for day');
+    
+    const res = await fetch(`http://localhost:3000/api/v1/days/${testDate}`, {
+      headers: { 'Authorization': `Bearer ${apiKey}` },
+    });
+    const json = await res.json();
+    expect(json.data).toBeDefined();
+    expect(json.data.events).toBeDefined();
+    expect(Array.isArray(json.data.events)).toBe(true);
+  });
+
+  it('should reject unauthorized request', async () => {
+    const res = await fetch('http://localhost:3000/api/v1/events', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({
+        date: testDate,
+        type: 'text',
+        content: 'Test',
+      }),
+    });
+    expect(res.status).toBe(401);
+  });
+});
diff --git a/backend/src/__tests__/export-import.test.ts b/backend/src/__tests__/export-import.test.ts
new file mode 100644
index 0000000..0a08cfa
--- /dev/null
+++ b/backend/src/__tests__/export-import.test.ts
@@ -0,0 +1,61 @@
+import { describe, it, expect, beforeEach } from 'bun:test';
+import { getApiKey, createEvent } from './helpers';
+
+describe('Export/Import API', () => {
+  let apiKey: string;
+  const testDate = '2026-03-29';
+
+  beforeEach(async () => {
+    apiKey = await getApiKey();
+    await createEvent(apiKey, testDate, 'text', 'Exportable event');
+  });
+
+  it('should export user data', async () => {
+    const res = await fetch('http://localhost:3000/api/v1/export', {
+      headers: { 'Authorization': `Bearer ${apiKey}` },
+    });
+    const json = await res.json();
+    expect(json.data).toBeDefined();
+    expect(json.data.version).toBeDefined();
+    expect(json.data.events).toBeDefined();
+    expect(json.data.journals).toBeDefined();
+    expect(json.data.settings).toBeDefined();
+    expect(Array.isArray(json.data.events)).toBe(true);
+    expect(Array.isArray(json.data.journals)).toBe(true);
+  });
+
+  it('should export events with location', async () => {
+    await fetch('http://localhost:3000/api/v1/events', {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json',
+        'Authorization': `Bearer ${apiKey}`,
+      },
+      body: JSON.stringify({
+        date: testDate,
+        type: 'text',
+        content: 'Event with location for export',
+        latitude: 51.5074,
+        longitude: -0.1278,
+        placeName: 'London, UK',
+      }),
+    });
+
+    const res = await fetch('http://localhost:3000/api/v1/export', {
+      headers: { 'Authorization': `Bearer ${apiKey}` },
+    });
+    const json = await res.json();
+    
+    const exportedEvent = json.data.events.find(
+      (e: any) => e.content === 'Event with location for export'
+    );
+    expect(exportedEvent).toBeDefined();
+    expect(exportedEvent.latitude).toBe(51.5074);
+    expect(exportedEvent.placeName).toBe('London, UK');
+  });
+
+  it('should reject unauthorized export', async () => {
+    const res = await fetch('http://localhost:3000/api/v1/export');
+    expect(res.status).toBe(401);
+  });
+});
diff --git a/backend/src/__tests__/helpers.ts b/backend/src/__tests__/helpers.ts
new file mode 100644
index 0000000..6605843
--- /dev/null
+++ b/backend/src/__tests__/helpers.ts
@@ -0,0 +1,95 @@
+import { describe, it, expect, beforeAll, afterAll } from 'bun:test';
+import { PrismaClient } from '@prisma/client';
+
+export const prisma = new PrismaClient({
+  datasourceUrl: 'file:./data/test.db',
+});
+
+export const TEST_USER = {
+  email: 'test@example.com',
+  password: 'testpassword123',
+};
+
+export const SECOND_USER = {
+  email: 'second@example.com',
+  password: 'secondpassword123',
+};
+
+let testApiKey: string;
+let secondApiKey: string;
+
+export async function createTestUser(email: string, password: string): Promise<string> {
+  const res = await fetch('http://localhost:3000/api/v1/auth/register', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ email, password }),
+  });
+  const json = await res.json();
+  return json.data.apiKey;
+}
+
+export async function loginUser(email: string, password: string): Promise<string> {
+  const res = await fetch('http://localhost:3000/api/v1/auth/login', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ email, password }),
+  });
+  const json = await res.json();
+  
+  const loginRes = await fetch('http://localhost:3000/api/v1/auth/api-key', {
+    method: 'POST',
+    headers: { 
+      'Content-Type': 'application/json',
+      'Authorization': `Bearer ${json.data.token}`,
+    },
+  });
+  const keyJson = await loginRes.json();
+  return keyJson.data.apiKey;
+}
+
+export async function createEvent(apiKey: string, date: string, type: string, content: string) {
+  const res = await fetch('http://localhost:3000/api/v1/events', {
+    method: 'POST',
+    headers: {
+      'Content-Type': 'application/json',
+      'Authorization': `Bearer ${apiKey}`,
+    },
+    body: JSON.stringify({ date, type, content }),
+  });
+  return res.json();
+}
+
+export async function getApiKey() {
+  if (!testApiKey) {
+    try {
+      testApiKey = await createTestUser(TEST_USER.email, TEST_USER.password);
+    } catch {
+      testApiKey = await loginUser(TEST_USER.email, TEST_USER.password);
+    }
+  }
+  return testApiKey;
+}
+
+export async function getSecondApiKey() {
+  if (!secondApiKey) {
+    try {
+      secondApiKey = await createTestUser(SECOND_USER.email, SECOND_USER.password);
+    } catch {
+      secondApiKey = await loginUser(SECOND_USER.email, SECOND_USER.password);
+    }
+  }
+  return secondApiKey;
+}
+
+beforeAll(async () => {
+  await prisma.event.deleteMany({ where: { user: { email: TEST_USER.email } } });
+  await prisma.journal.deleteMany({ where: { user: { email: TEST_USER.email } } });
+  await prisma.task.deleteMany({ where: { user: { email: TEST_USER.email } } });
+  await prisma.event.deleteMany({ where: { user: { email: SECOND_USER.email } } });
+  await prisma.journal.deleteMany({ where: { user: { email: SECOND_USER.email } } });
+  await prisma.task.deleteMany({ where: { user: { email: SECOND_USER.email } } });
+});
+
+afterAll(async () => {
+  await prisma.$disconnect();
+});
diff --git a/backend/src/__tests__/journals.test.ts b/backend/src/__tests__/journals.test.ts
new file mode 100644
index 0000000..ed1cf7d
--- /dev/null
+++ b/backend/src/__tests__/journals.test.ts
@@ -0,0 +1,55 @@
+import { describe, it, expect, beforeEach } from 'bun:test';
+import { getApiKey, createEvent } from './helpers';
+
+describe('Journals API', () => {
+  let apiKey: string;
+  const testDate = '2026-03-28';
+
+  beforeEach(async () => {
+    apiKey = await getApiKey();
+  });
+
+  it('should get empty day for journal', async () => {
+    const res = await fetch(`http://localhost:3000/api/v1/journal/${testDate}`, {
+      headers: { 'Authorization': `Bearer ${apiKey}` },
+    });
+    const json = await res.json();
+    expect(res.status).toBe(404);
+    expect(json.error.code).toBe('NOT_FOUND');
+  });
+
+  it('should reject journal generation with no events', async () => {
+    const res = await fetch(`http://localhost:3000/api/v1/journal/generate/${testDate}`, {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json',
+        'Authorization': `Bearer ${apiKey}`,
+      },
+    });
+    const json = await res.json();
+    expect(res.status).toBe(400);
+    expect(json.error.code).toBe('NO_EVENTS');
+  });
+
+  it('should delete journal', async () => {
+    await createEvent(apiKey, testDate, 'text', 'Test event');
+    
+    const deleteRes = await fetch(`http://localhost:3000/api/v1/journal/${testDate}`, {
+      method: 'DELETE',
+      headers: { 'Authorization': `Bearer ${apiKey}` },
+    });
+    const json = await deleteRes.json();
+    expect(json.data.deleted).toBe(true);
+  });
+
+  it('should list journals with pagination', async () => {
+    const res = await fetch('http://localhost:3000/api/v1/journals?page=1&limit=10', {
+      headers: { 'Authorization': `Bearer ${apiKey}` },
+    });
+    const json = await res.json();
+    expect(json.data.journals).toBeDefined();
+    expect(json.data.total).toBeDefined();
+    expect(json.data.page).toBe(1);
+    expect(json.data.limit).toBe(10);
+  });
+});
diff --git a/backend/src/__tests__/search.test.ts b/backend/src/__tests__/search.test.ts
new file mode 100644
index 0000000..f3a0ccd
--- /dev/null
+++ b/backend/src/__tests__/search.test.ts
@@ -0,0 +1,40 @@
+import { describe, it, expect, beforeEach } from 'bun:test';
+import { getApiKey, createEvent } from './helpers';
+
+describe('Search API', () => {
+  let apiKey: string;
+
+  beforeEach(async () => {
+    apiKey = await getApiKey();
+  });
+
+  it('should search events', async () => {
+    await createEvent(apiKey, '2026-03-30', 'text', 'Unique search term banana apple');
+    
+    const res = await fetch('http://localhost:3000/api/v1/search?q=banana', {
+      headers: { 'Authorization': `Bearer ${apiKey}` },
+    });
+    const json = await res.json();
+    expect(json.data).toBeDefined();
+    expect(json.data.events).toBeDefined();
+  });
+
+  it('should return empty results for no matches', async () => {
+    const res = await fetch('http://localhost:3000/api/v1/search?q=nonexistentterm12345', {
+      headers: { 'Authorization': `Bearer ${apiKey}` },
+    });
+    const json = await res.json();
+    expect(json.data.events.length).toBe(0);
+  });
+
+  it('should search across all dates', async () => {
+    await createEvent(apiKey, '2026-03-15', 'text', 'Searchable content from march');
+    await createEvent(apiKey, '2026-03-20', 'text', 'Searchable content from march again');
+    
+    const res = await fetch('http://localhost:3000/api/v1/search?q=march', {
+      headers: { 'Authorization': `Bearer ${apiKey}` },
+    });
+    const json = await res.json();
+    expect(json.data.events.length).toBeGreaterThanOrEqual(2);
+  });
+});
diff --git a/backend/src/__tests__/settings.test.ts b/backend/src/__tests__/settings.test.ts
new file mode 100644
index 0000000..20905d1
--- /dev/null
+++ b/backend/src/__tests__/settings.test.ts
@@ -0,0 +1,71 @@
+import { describe, it, expect, beforeEach } from 'bun:test';
+import { getApiKey } from './helpers';
+
+describe('Settings API', () => {
+  let apiKey: string;
+
+  beforeEach(async () => {
+    apiKey = await getApiKey();
+  });
+
+  it('should get default settings', async () => {
+    const res = await fetch('http://localhost:3000/api/v1/settings', {
+      headers: { 'Authorization': `Bearer ${apiKey}` },
+    });
+    const json = await res.json();
+    expect(json.data).toBeDefined();
+    expect(json.data.aiProvider).toBeDefined();
+  });
+
+  it('should update settings', async () => {
+    const res = await fetch('http://localhost:3000/api/v1/settings', {
+      method: 'PUT',
+      headers: {
+        'Content-Type': 'application/json',
+        'Authorization': `Bearer ${apiKey}`,
+      },
+      body: JSON.stringify({
+        aiProvider: 'openai',
+        journalPrompt: 'Write in a poetic style',
+      }),
+    });
+    const json = await res.json();
+    expect(json.data.aiProvider).toBe('openai');
+    expect(json.data.journalPrompt).toBe('Write in a poetic style');
+  });
+
+  it('should clear journal prompt with empty string', async () => {
+    await fetch('http://localhost:3000/api/v1/settings', {
+      method: 'PUT',
+      headers: {
+        'Content-Type': 'application/json',
+        'Authorization': `Bearer ${apiKey}`,
+      },
+      body: JSON.stringify({ journalPrompt: '' }),
+    });
+    
+    const getRes = await fetch('http://localhost:3000/api/v1/settings', {
+      headers: { 'Authorization': `Bearer ${apiKey}` },
+    });
+    const json = await getRes.json();
+    expect(json.data.journalPrompt).toBeNull();
+  });
+
+  it('should change password', async () => {
+    const newPassword = 'newpassword456';
+    
+    const res = await fetch('http://localhost:3000/api/v1/account/password', {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json',
+        'Authorization': `Bearer ${apiKey}`,
+      },
+      body: JSON.stringify({
+        currentPassword: 'testpassword123',
+        newPassword,
+      }),
+    });
+    const json = await res.json();
+    expect(json.data).toBeDefined();
+  });
+});