diff --git a/vitest.config.ts b/vitest.config.ts
index 57d46a6..1f89716 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -4,6 +4,6 @@ export default defineConfig({
   test: {
     root: '.',
     environment: 'node',
-    include: ['src/**/*.test.ts'],
+    include: ['src/**/*.test.ts', 'web/src/**/*.test.ts'],
   },
 });
diff --git a/web/src/api.test.ts b/web/src/api.test.ts
new file mode 100644
index 0000000..d5c5c5a
--- /dev/null
+++ b/web/src/api.test.ts
@@ -0,0 +1,36 @@
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { api } from './api';
+
+afterEach(() => vi.unstubAllGlobals());
+
+describe('API requests', () => {
+  it('does not send a content type for a bodyless request', async () => {
+    const fetchMock = vi.fn().mockResolvedValue(new Response(null, { status: 204 }));
+    vi.stubGlobal('fetch', fetchMock);
+
+    await api('/api/hosts/1/test', { method: 'POST' });
+
+    const options = fetchMock.mock.calls[0]![1] as RequestInit;
+    expect((options.headers as Headers).has('content-type')).toBe(false);
+  });
+
+  it('sends JSON content type when a body is present', async () => {
+    const fetchMock = vi.fn().mockResolvedValue(Response.json({ saved: true }));
+    vi.stubGlobal('fetch', fetchMock);
+
+    await api('/api/hosts', { method: 'POST', body: JSON.stringify({ name: 'server' }) });
+
+    const options = fetchMock.mock.calls[0]![1] as RequestInit;
+    expect((options.headers as Headers).get('content-type')).toBe('application/json');
+  });
+
+  it('preserves an explicitly supplied content type', async () => {
+    const fetchMock = vi.fn().mockResolvedValue(Response.json({ saved: true }));
+    vi.stubGlobal('fetch', fetchMock);
+
+    await api('/api/import', { method: 'POST', headers: { 'content-type': 'text/plain' }, body: 'value' });
+
+    const options = fetchMock.mock.calls[0]![1] as RequestInit;
+    expect((options.headers as Headers).get('content-type')).toBe('text/plain');
+  });
+});
diff --git a/web/src/api.ts b/web/src/api.ts
new file mode 100644
index 0000000..31e1495
--- /dev/null
+++ b/web/src/api.ts
@@ -0,0 +1,10 @@
+export async function api<T>(url: string, options?: RequestInit): Promise<T> {
+  const headers = new Headers(options?.headers);
+  if (options?.body != null && !headers.has('content-type')) headers.set('content-type', 'application/json');
+
+  const response = await fetch(url, { ...options, headers });
+  if (response.status === 204) return undefined as T;
+  const body = await response.json();
+  if (!response.ok) throw new Error(body.error ?? 'Request failed');
+  return body as T;
+}
diff --git a/web/src/main.tsx b/web/src/main.tsx
index d3204cf..9714b8e 100644
--- a/web/src/main.tsx
+++ b/web/src/main.tsx
@@ -1,5 +1,6 @@
 import { FormEvent, useEffect, useState } from 'react';
 import { createRoot } from 'react-dom/client';
+import { api } from './api';
 import './styles.css';
 
 type Tab = 'overview' | 'hosts' | 'jobs' | 'settings';
@@ -15,17 +16,6 @@ type Job = { id: number; name: string; hostName: string; config: { steps: Array<
 type Run = { id: number; jobName: string; status: string; trigger: string; createdAt: string; startedAt?: string; finishedAt?: string; error?: string; artifactCount: number };
 type RunDetail = { run: { id: number; status: string; log: string; error?: string }; artifacts: Array<{ id: number; name: string; size: number; checksum: string }> };
 
-async function api<T>(url: string, options?: RequestInit): Promise<T> {
-  const response = await fetch(url, {
-    ...options,
-    headers: { 'content-type': 'application/json', ...options?.headers },
-  });
-  if (response.status === 204) return undefined as T;
-  const body = await response.json();
-  if (!response.ok) throw new Error(body.error ?? 'Request failed');
-  return body as T;
-}
-
 function Login({ onLogin }: { onLogin: () => void }) {
   const [error, setError] = useState('');
   async function submit(event: FormEvent<HTMLFormElement>) {