diff --git a/test/fetch.test.ts b/test/fetch.test.ts
new file mode 100644
index 0000000..9ac20cf
--- /dev/null
+++ b/test/fetch.test.ts
@@ -0,0 +1,179 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { fetchHeaders } from '../src/fetch.js';
+
+describe('fetchHeaders', () => {
+  beforeEach(() => {
+    vi.stubGlobal('fetch', vi.fn());
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+    vi.unstubAllGlobals();
+  });
+
+  function mockFetch(headers: Record<string, string> = {}, body: ReadableStream | null = null) {
+    vi.mocked(fetch).mockResolvedValue({
+      headers: new Headers(headers),
+      body,
+    } as unknown as Response);
+  }
+
+  it('returns response headers as lowercase key-value pairs', async () => {
+    mockFetch({
+      'Content-Type': 'text/html',
+      'X-Frame-Options': 'DENY',
+      'Strict-Transport-Security': 'max-age=31536000',
+    });
+
+    const result = await fetchHeaders('https://example.com');
+
+    expect(result).toEqual({
+      'content-type': 'text/html',
+      'x-frame-options': 'DENY',
+      'strict-transport-security': 'max-age=31536000',
+    });
+  });
+
+  it('uses GET method with redirect:follow', async () => {
+    mockFetch();
+
+    await fetchHeaders('https://example.com');
+
+    expect(fetch).toHaveBeenCalledWith(
+      'https://example.com',
+      expect.objectContaining({ method: 'GET', redirect: 'follow' }),
+    );
+  });
+
+  it('passes an AbortSignal to fetch', async () => {
+    mockFetch();
+
+    await fetchHeaders('https://example.com');
+
+    expect(fetch).toHaveBeenCalledWith(
+      'https://example.com',
+      expect.objectContaining({ signal: expect.any(AbortSignal) }),
+    );
+  });
+
+  it('cancels the response body to free resources', async () => {
+    const cancel = vi.fn().mockResolvedValue(undefined);
+    vi.mocked(fetch).mockResolvedValue({
+      headers: new Headers(),
+      body: { cancel } as unknown as ReadableStream,
+    } as unknown as Response);
+
+    await fetchHeaders('https://example.com');
+
+    expect(cancel).toHaveBeenCalledOnce();
+  });
+
+  it('handles null body without throwing', async () => {
+    vi.mocked(fetch).mockResolvedValue({
+      headers: new Headers(),
+      body: null,
+    } as unknown as Response);
+
+    await expect(fetchHeaders('https://example.com')).resolves.toEqual({});
+  });
+
+  it('returns empty object when no headers are present', async () => {
+    mockFetch();
+    const result = await fetchHeaders('https://example.com');
+    expect(result).toEqual({});
+  });
+
+  it('propagates network errors', async () => {
+    vi.mocked(fetch).mockRejectedValue(new TypeError('Failed to fetch'));
+
+    await expect(fetchHeaders('https://example.com')).rejects.toThrow('Failed to fetch');
+  });
+
+  it('aborts and rejects after the configured timeout', async () => {
+    vi.useFakeTimers();
+
+    let capturedSignal: AbortSignal | undefined;
+    vi.mocked(fetch).mockImplementation((_url, init) => {
+      capturedSignal = init?.signal as AbortSignal;
+      return new Promise((_resolve, reject) => {
+        capturedSignal?.addEventListener('abort', () =>
+          reject(new DOMException('The operation was aborted.', 'AbortError')),
+        );
+      });
+    });
+
+    const promise = fetchHeaders('https://example.com', { timeoutMs: 1000 });
+    // Attach rejection handler before advancing timers to avoid unhandled-rejection warnings.
+    promise.catch(() => {});
+
+    await vi.advanceTimersByTimeAsync(1001);
+
+    await expect(promise).rejects.toMatchObject({ name: 'AbortError' });
+    expect(capturedSignal?.aborted).toBe(true);
+
+    vi.useRealTimers();
+  });
+
+  it('does not abort before the timeout elapses', async () => {
+    vi.useFakeTimers();
+
+    let capturedSignal: AbortSignal | undefined;
+    vi.mocked(fetch).mockImplementation((_url, init) => {
+      capturedSignal = init?.signal as AbortSignal;
+      return new Promise(() => {});
+    });
+
+    fetchHeaders('https://example.com', { timeoutMs: 5000 }).catch(() => {});
+    await vi.advanceTimersByTimeAsync(4999);
+
+    expect(capturedSignal?.aborted).toBe(false);
+
+    vi.useRealTimers();
+  });
+
+  it('uses 10 seconds as the default timeout', async () => {
+    vi.useFakeTimers();
+
+    let capturedSignal: AbortSignal | undefined;
+    vi.mocked(fetch).mockImplementation((_url, init) => {
+      capturedSignal = init?.signal as AbortSignal;
+      return new Promise((_resolve, reject) => {
+        capturedSignal?.addEventListener('abort', () =>
+          reject(new DOMException('Aborted', 'AbortError')),
+        );
+      });
+    });
+
+    const promise = fetchHeaders('https://example.com');
+    // Attach rejection handler before advancing timers to avoid unhandled-rejection warnings.
+    promise.catch(() => {});
+
+    await vi.advanceTimersByTimeAsync(9999);
+    expect(capturedSignal?.aborted).toBe(false);
+
+    await vi.advanceTimersByTimeAsync(1);
+    expect(capturedSignal?.aborted).toBe(true);
+
+    await expect(promise).rejects.toMatchObject({ name: 'AbortError' });
+
+    vi.useRealTimers();
+  });
+
+  it('clears the timer after a successful fetch', async () => {
+    const clearTimeoutSpy = vi.spyOn(globalThis, 'clearTimeout');
+    mockFetch({ 'x-test': 'value' });
+
+    await fetchHeaders('https://example.com');
+
+    expect(clearTimeoutSpy).toHaveBeenCalledOnce();
+  });
+
+  it('clears the timer even when fetch throws', async () => {
+    const clearTimeoutSpy = vi.spyOn(globalThis, 'clearTimeout');
+    vi.mocked(fetch).mockRejectedValue(new Error('oops'));
+
+    await fetchHeaders('https://example.com').catch(() => {});
+
+    expect(clearTimeoutSpy).toHaveBeenCalledOnce();
+  });
+});