diff --git a/tests/unit/web-server/auth-check-remote-access.test.ts b/tests/unit/web-server/auth-check-remote-access.test.ts
new file mode 100644
index 00000000..6d00d053
--- /dev/null
+++ b/tests/unit/web-server/auth-check-remote-access.test.ts
@@ -0,0 +1,63 @@
+/**
+ * Auth Check Route — Remote Access Detection Tests
+ *
+ * Verifies that /api/auth/check returns effectiveAuthRequired=true
+ * for remote clients when auth is disabled, preventing a silently
+ * broken dashboard.
+ */
+
+import { describe, it, expect } from 'bun:test';
+import { isLoopbackRemoteAddress } from '../../../src/web-server/middleware/auth-middleware';
+
+describe('isLoopbackRemoteAddress', () => {
+  it('returns true for IPv4 localhost', () => {
+    expect(isLoopbackRemoteAddress('127.0.0.1')).toBe(true);
+  });
+
+  it('returns true for IPv6 localhost', () => {
+    expect(isLoopbackRemoteAddress('::1')).toBe(true);
+  });
+
+  it('returns true for IPv4-mapped IPv6 localhost', () => {
+    expect(isLoopbackRemoteAddress('::ffff:127.0.0.1')).toBe(true);
+  });
+
+  it('returns true for other loopback addresses', () => {
+    expect(isLoopbackRemoteAddress('127.0.0.2')).toBe(true);
+    expect(isLoopbackRemoteAddress('::ffff:127.0.0.2')).toBe(true);
+  });
+
+  it('returns false for LAN addresses', () => {
+    expect(isLoopbackRemoteAddress('192.168.1.100')).toBe(false);
+    expect(isLoopbackRemoteAddress('10.0.0.1')).toBe(false);
+  });
+
+  it('returns false for undefined', () => {
+    expect(isLoopbackRemoteAddress(undefined)).toBe(false);
+  });
+});
+
+describe('effectiveAuthRequired logic', () => {
+  // Mirrors the logic in auth-routes.ts GET /api/auth/check:
+  // effectiveAuthRequired = authConfig.enabled || !isLocal
+  function computeEffectiveAuthRequired(authEnabled: boolean, remoteAddress: string | undefined) {
+    const isLocal = isLoopbackRemoteAddress(remoteAddress);
+    return authEnabled || !isLocal;
+  }
+
+  it('localhost + auth disabled -> authRequired=false', () => {
+    expect(computeEffectiveAuthRequired(false, '127.0.0.1')).toBe(false);
+  });
+
+  it('remote + auth disabled -> authRequired=true', () => {
+    expect(computeEffectiveAuthRequired(false, '192.168.2.100')).toBe(true);
+  });
+
+  it('remote + auth enabled -> authRequired=true', () => {
+    expect(computeEffectiveAuthRequired(true, '192.168.2.100')).toBe(true);
+  });
+
+  it('localhost + auth enabled -> authRequired=true', () => {
+    expect(computeEffectiveAuthRequired(true, '127.0.0.1')).toBe(true);
+  });
+});