diff --git a/src/lib/api-client.test.ts b/src/lib/api-client.test.ts
new file mode 100644
index 0000000..a64a5eb
--- /dev/null
+++ b/src/lib/api-client.test.ts
@@ -0,0 +1,105 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+import { ApiClientError, cardsApi } from './api-client'
+
+const CARD = {
+  id: '10000000-0000-4000-8000-000000000001',
+  question: 'Q ?',
+  response: 'R',
+  theme: 'git',
+  tags: ['a'],
+  createdAt: '2026-01-01T08:00:00.000Z',
+  updatedAt: '2026-01-01T08:00:00.000Z',
+}
+
+const jsonResponse = (body: unknown, status = 200) =>
+  new Response(JSON.stringify(body), { status, headers: { 'Content-Type': 'application/json' } })
+
+const fetchMock = vi.fn()
+
+beforeEach(() => {
+  global.fetch = fetchMock as unknown as typeof fetch
+  fetchMock.mockReset()
+})
+
+function expectRequest(method: string, path: string) {
+  expect(fetchMock).toHaveBeenCalledWith(
+    path,
+    expect.objectContaining({ method }),
+  )
+}
+
+describe('cardsApi', () => {
+  it('list() appelle GET /api/cards', async () => {
+    fetchMock.mockResolvedValue(jsonResponse([CARD]))
+    await expect(cardsApi.list()).resolves.toEqual([CARD])
+    expectRequest('GET', '/api/cards')
+  })
+
+  it('get() appelle GET /api/cards/:id', async () => {
+    fetchMock.mockResolvedValue(jsonResponse(CARD))
+    await expect(cardsApi.get(CARD.id)).resolves.toEqual(CARD)
+    expectRequest('GET', `/api/cards/${CARD.id}`)
+  })
+
+  it('create() envoie POST avec un corps JSON', async () => {
+    fetchMock.mockResolvedValue(jsonResponse(CARD, 201))
+    await expect(cardsApi.create({ question: 'Q ?', response: 'R', theme: 'git' } as never)).resolves.toEqual(CARD)
+    const [_, init] = fetchMock.mock.calls[0]
+    expect(init.method).toBe('POST')
+    expect(JSON.parse(init.body)).toEqual({ question: 'Q ?', response: 'R', theme: 'git' })
+  })
+
+  it('update() envoie PUT /api/cards/:id', async () => {
+    fetchMock.mockResolvedValue(jsonResponse(CARD))
+    await expect(cardsApi.update(CARD.id, { question: 'Q ?' } as never)).resolves.toEqual(CARD)
+    expectRequest('PUT', `/api/cards/${CARD.id}`)
+  })
+
+  it('remove() envoie DELETE et ignore le corps', async () => {
+    fetchMock.mockResolvedValue(new Response(null, { status: 204 }))
+    await expect(cardsApi.remove(CARD.id)).resolves.toBeUndefined()
+    expectRequest('DELETE', `/api/cards/${CARD.id}`)
+  })
+
+  it('random() sans thème et avec thème (URL-encodé)', async () => {
+    fetchMock.mockResolvedValue(jsonResponse(CARD))
+    await cardsApi.random()
+    expectRequest('GET', '/api/cards/random')
+    await cardsApi.random('git ops')
+    expectRequest('GET', '/api/cards/random?theme=git%20ops')
+  })
+
+  it('themes() appelle GET /api/themes', async () => {
+    fetchMock.mockResolvedValue(jsonResponse(['git', 'docker']))
+    await expect(cardsApi.themes()).resolves.toEqual(['git', 'docker'])
+    expectRequest('GET', '/api/themes')
+  })
+
+  it('lève ApiClientError avec le message de l API sur une erreur 404', async () => {
+    fetchMock.mockResolvedValue(jsonResponse({ error: 'NotFoundError', message: 'Carte inconnue' }, 404))
+    await expect(cardsApi.get('nope')).rejects.toMatchObject({
+      name: 'NotFoundError',
+      message: 'Carte inconnue',
+      status: 404,
+    })
+  })
+
+  it('lève ApiClientError sur une réponse invalide', async () => {
+    fetchMock.mockResolvedValue(jsonResponse({ error: 'ValidationError', message: 'Payload invalide' }, 400))
+    await expect(cardsApi.create({} as never)).rejects.toBeInstanceOf(ApiClientError)
+  })
+
+  it('lève ApiClientError NetworkError quand fetch échoue', async () => {
+    fetchMock.mockRejectedValue(new TypeError('network'))
+    await expect(cardsApi.list()).rejects.toMatchObject({ name: 'NetworkError', status: 0 })
+  })
+})
+
+describe('ApiClientError', () => {
+  it('porte status, name et message', () => {
+    const err = new ApiClientError(404, 'NotFoundError', 'inconnu')
+    expect(err.status).toBe(404)
+    expect(err.name).toBe('NotFoundError')
+    expect(err.message).toBe('inconnu')
+  })
+})
diff --git a/src/lib/api-client.ts b/src/lib/api-client.ts
new file mode 100644
index 0000000..4d16270
--- /dev/null
+++ b/src/lib/api-client.ts
@@ -0,0 +1,47 @@
+import type { Card, CardInput } from '@/domain/card'
+
+export class ApiClientError extends Error {
+  status: number
+  constructor(status: number, error: string, message: string) {
+    super(message)
+    this.name = error
+    this.status = status
+  }
+}
+
+interface ApiErrorPayload {
+  error?: string
+  message?: string
+}
+
+async function request<T>(path: string, init?: RequestInit): Promise<T> {
+  let res: Response
+  try {
+    res = await fetch(path, {
+      method: init?.method ?? 'GET',
+      ...init,
+      headers: { 'Content-Type': 'application/json', ...init?.headers },
+    })
+  } catch {
+    throw new ApiClientError(0, 'NetworkError', 'Impossible de joindre le serveur')
+  }
+  if (res.status === 204) return undefined as T
+  const body: T | ApiErrorPayload = await res.json().catch(() => ({}))
+  if (!res.ok) {
+    const payload = body as ApiErrorPayload
+    throw new ApiClientError(res.status, payload.error ?? 'HttpError', payload.message ?? `Erreur ${res.status}`)
+  }
+  return body as T
+}
+
+export const cardsApi = {
+  list: () => request<Card[]>('/api/cards'),
+  get: (id: string) => request<Card>(`/api/cards/${id}`),
+  create: (input: CardInput) => request<Card>('/api/cards', { method: 'POST', body: JSON.stringify(input) }),
+  update: (id: string, input: CardInput) =>
+    request<Card>(`/api/cards/${id}`, { method: 'PUT', body: JSON.stringify(input) }),
+  remove: (id: string) => request<void>(`/api/cards/${id}`, { method: 'DELETE' }),
+  random: (theme?: string) =>
+    request<Card>(`/api/cards/random${theme ? `?theme=${encodeURIComponent(theme)}` : ''}`),
+  themes: () => request<string[]>('/api/themes'),
+}