diff --git a/services/platform-service/src/lib/config.test.ts b/services/platform-service/src/lib/config.test.ts
new file mode 100644
index 00000000..3388bee4
--- /dev/null
+++ b/services/platform-service/src/lib/config.test.ts
@@ -0,0 +1,53 @@
+import { afterEach, describe, expect, it, vi } from 'vitest';
+
+const REQUIRED_ENV = {
+  COSMOS_ENDPOINT: 'https://example.documents.azure.com:443/',
+  COSMOS_KEY: 'test-cosmos-key',
+  JWT_SECRET: 'test-jwt-secret',
+};
+
+afterEach(() => {
+  vi.resetModules();
+  vi.unstubAllEnvs();
+});
+
+describe('lib/config', () => {
+  it('parses with defaults when required env vars are set', async () => {
+    vi.stubEnv('COSMOS_ENDPOINT', REQUIRED_ENV.COSMOS_ENDPOINT);
+    vi.stubEnv('COSMOS_KEY', REQUIRED_ENV.COSMOS_KEY);
+    vi.stubEnv('JWT_SECRET', REQUIRED_ENV.JWT_SECRET);
+
+    const { config } = await import('./config.js');
+
+    expect(config.PORT).toBe(4003);
+    expect(config.HOST).toBe('0.0.0.0');
+    expect(['development', 'test']).toContain(config.NODE_ENV);
+    expect(config.COSMOS_DATABASE).toBe('lysnrai');
+    expect(config.USAGE_WARN_THRESHOLD).toBe(0.8);
+  });
+
+  it('respects explicit env overrides', async () => {
+    vi.stubEnv('COSMOS_ENDPOINT', REQUIRED_ENV.COSMOS_ENDPOINT);
+    vi.stubEnv('COSMOS_KEY', REQUIRED_ENV.COSMOS_KEY);
+    vi.stubEnv('JWT_SECRET', REQUIRED_ENV.JWT_SECRET);
+    vi.stubEnv('PORT', '4999');
+    vi.stubEnv('NODE_ENV', 'test');
+    vi.stubEnv('SERVICE_NAME', 'platform-service-test');
+    vi.stubEnv('USAGE_WARN_THRESHOLD', '0.9');
+
+    const { config } = await import('./config.js');
+
+    expect(config.PORT).toBe(4999);
+    expect(config.NODE_ENV).toBe('test');
+    expect(config.SERVICE_NAME).toBe('platform-service-test');
+    expect(config.USAGE_WARN_THRESHOLD).toBe(0.9);
+  });
+
+  it('throws when required env vars are missing', async () => {
+    vi.stubEnv('COSMOS_ENDPOINT', '');
+    vi.stubEnv('COSMOS_KEY', '');
+    vi.stubEnv('JWT_SECRET', '');
+
+    await expect(import('./config.js')).rejects.toThrow();
+  });
+});