diff --git a/e2e/environment.spec.ts b/e2e/environment.spec.ts
index 6d1d825..5b36a80 100644
--- a/e2e/environment.spec.ts
+++ b/e2e/environment.spec.ts
@@ -156,4 +156,58 @@ test.describe('Environment Management', () => {
     const pageContent = await page.content();
     expect(pageContent).toContain('!!! custom');
   });
+
+  test('should not duplicate params when placeholder already exists in template', async ({ page }) => {
+    await page.goto('/');
+    await page.click('button:has-text("Create new")');
+
+    // Step 1: Add a param to DEFAULT
+    const nameInput = page.locator('input[placeholder="name"]').first();
+    const valueInput = page.locator('input[placeholder="value"]').first();
+    const addButton = page.locator('button.btn-success').first();
+    
+    await nameInput.fill('host');
+    await valueInput.fill('localhost:8080');
+    await addButton.click();
+    await page.waitForTimeout(500);
+
+    // Step 2: Switch to Content Template tab
+    await page.click('a:has-text("Content Template")');
+    await page.waitForTimeout(500);
+
+    // Step 3: Click Edit and manually add @host@ usage in a custom field
+    await page.click('button:has-text("Edit")');
+    await page.waitForTimeout(300);
+
+    const textarea = page.locator('textarea');
+    // Add a custom field that uses @host@ placeholder
+    await textarea.fill('{\n    "!!! host": "@host@",\n    "apiUrl": "http://@host@/api"\n}');
+    await page.waitForTimeout(300);
+
+    // Step 4: Save
+    await page.click('button:has-text("Save")');
+    await page.waitForTimeout(500);
+
+    // Step 5: Add ANOTHER param with same name (host) - should not create duplicate
+    await page.click('a:has-text("Env")');
+    await page.waitForTimeout(300);
+    
+    await nameInput.fill('host');
+    await valueInput.fill('updated-host:9090');
+    await addButton.click();
+    await page.waitForTimeout(500);
+
+    // Step 6: Switch back to Content Template and verify no duplicate
+    await page.click('a:has-text("Content Template")');
+    await page.waitForTimeout(500);
+
+    // Count occurrences of "!!! host" - should be exactly 1
+    const templateContent = await page.locator('.config-template-editor').textContent();
+    const hostKeyCount = (templateContent.match(/!!! host/g) || []).length;
+    expect(hostKeyCount).toBe(1);
+
+    // The @host@ placeholder should appear twice (once in !!! host, once in apiUrl)
+    const hostPlaceholderCount = (templateContent.match(/@host@/g) || []).length;
+    expect(hostPlaceholderCount).toBe(2);
+  });
 });