diff --git a/src/lib/validation.test.ts b/src/lib/validation.test.ts
new file mode 100644
index 0000000..b9bfde1
--- /dev/null
+++ b/src/lib/validation.test.ts
@@ -0,0 +1,70 @@
+import { test } from 'node:test';
+import assert from 'node:assert';
+import { calculateExpiration, calculateTTL } from './validation.ts';
+
+test('calculateTTL', async (t) => {
+    t.mock.timers.enable({ apis: ['Date'] });
+    const now = 1000000;
+    t.mock.timers.setTime(now);
+
+    await t.test('should return undefined when expiresAt is undefined', () => {
+        assert.strictEqual(calculateTTL(undefined), undefined);
+    });
+
+    await t.test('should return positive seconds for future timestamp', () => {
+        const future = now + 5000;
+        assert.strictEqual(calculateTTL(future), 5);
+    });
+
+    await t.test('should return 0 for past timestamp (edge case)', () => {
+        const past = now - 5000;
+        assert.strictEqual(calculateTTL(past), 0);
+    });
+
+    await t.test('should return 0 for current timestamp', () => {
+        assert.strictEqual(calculateTTL(now), 0);
+    });
+
+    await t.test('should floor the result', () => {
+        const future = now + 5500;
+        assert.strictEqual(calculateTTL(future), 5);
+    });
+});
+
+test('calculateExpiration', async (t) => {
+    t.mock.timers.enable({ apis: ['Date'] });
+    const now = 1000000;
+    t.mock.timers.setTime(now);
+
+    await t.test('should return undefined for "never"', () => {
+        assert.strictEqual(calculateExpiration('never'), undefined);
+    });
+
+    await t.test('should return now + 5 min', () => {
+        assert.strictEqual(calculateExpiration('5min'), now + 5 * 60 * 1000);
+    });
+
+    await t.test('should return now + 1 hour', () => {
+        assert.strictEqual(calculateExpiration('1hour'), now + 60 * 60 * 1000);
+    });
+
+    await t.test('should return now + 1 day', () => {
+        assert.strictEqual(calculateExpiration('1day'), now + 24 * 60 * 60 * 1000);
+    });
+
+    await t.test('should return now + 7 days', () => {
+        assert.strictEqual(calculateExpiration('7days'), now + 7 * 24 * 60 * 60 * 1000);
+    });
+
+    await t.test('should return now + 30 days', () => {
+        assert.strictEqual(calculateExpiration('30days'), now + 30 * 24 * 60 * 60 * 1000);
+    });
+
+    await t.test('should return undefined for "views"', () => {
+        assert.strictEqual(calculateExpiration('views'), undefined);
+    });
+
+    await t.test('should return undefined for "burn"', () => {
+        assert.strictEqual(calculateExpiration('burn'), undefined);
+    });
+});
diff --git a/src/lib/validation.ts b/src/lib/validation.ts
index e7504bc..c578ac7 100644
--- a/src/lib/validation.ts
+++ b/src/lib/validation.ts
@@ -138,9 +138,9 @@ export function calculateTTL(expiresAt?: number): number | undefined {
 /**
  * Re-export getClientIp from the dedicated IP utility module.
  */
-export { getClientIp } from './ip';
+export { getClientIp } from './ip.ts';
 
 /**
  * Re-export paste size validation logic from the dedicated module.
  */
-export { MAX_PASTE_SIZE, validatePasteSize } from './paste-size';
+export { MAX_PASTE_SIZE, validatePasteSize } from './paste-size.ts';