Testing with Slow Networks and Offline Mode
Simulate real-world network conditions to test loading states, error handling, and offline behavior.
Your users aren't all on fast WiFi. Many are on 3G connections, in elevators, or on flaky public networks. Certyn lets you simulate these conditions to verify your app handles them gracefully.
Network Presets
Certyn provides realistic network simulation via Chrome DevTools Protocol:
| Preset | Latency | Download | Upload |
|---|---|---|---|
| Slow 3G | 2000ms | 50 KB/s | 25 KB/s |
| 3G | 100ms | 188 KB/s | 94 KB/s |
| 4G | 20ms | 4 MB/s | 3 MB/s |
| WiFi | 2ms | 30 MB/s | 15 MB/s |
| Offline | - | 0 | 0 |
What to Test
Loading States
On slow networks, content takes time to appear. Does your app show:
- Skeleton screens or spinners?
- Progressive loading for images?
- Meaningful feedback during form submissions?
Error Handling
Switch to offline mode and verify:
- Does the app show a clear offline message?
- Are form submissions queued or do they fail silently?
- Does reconnecting recover gracefully?
Timeouts
On slow 3G, API calls may take 10+ seconds:
- Do requests timeout with a helpful message?
- Is there a retry mechanism?
- Does the UI remain responsive during long requests?
Example Scenarios
Test checkout on slow 3G
"Simulate slow 3G network and complete the checkout flow. Check if loading indicators appear and if the payment submission handles the delay."
Verify offline error handling
"Go offline and try to submit the contact form. Verify a proper error message appears, not a blank page or browser error."
Test image loading on 3G
"Switch to 3G and navigate to the product gallery. Check if images lazy load and if placeholders are shown."
Tips
- Always test your most critical flows on slow 3G — it exposes timing-related bugs
- Offline testing catches missing error boundaries
- Remember to
resetthe network after testing to avoid affecting subsequent test steps - Combine with mobile emulation for the most realistic user experience