Test on a slow network

Your app feels fine on your office Wi-Fi, but you need to know how it behaves on a train. This guide slows one host (or everything) down to 3G, high latency, or intermittent packet loss with the Network Conditions tool, confirms the effect in the traffic list and timeline, and turns it off cleanly.

What you need

Cloak Proxy capturing the app you want to test	See macOS traffic or Debug a mobile app
HTTPS decrypted for the host, if you want per-host throttling to match it	See SSL Proxying — throttling matches by URL, which needs the request decrypted

Note

Network Conditions throttles traffic that goes through Cloak Proxy. It shapes the proxy’s own transfer timing; it does not change the device’s radio or the operating system’s networking.

Add a condition for one host

1. Capture a request to the host, right-click it, and choose Tools → Network Conditions…. The rule is created matching that host (wildcard, subpaths included) and the tool is turned on.

   You can also open Tools → Network Conditions (<kbd>⌥</kbd> <kbd>⌘</kbd> <kbd>T</kbd>) and add a rule by hand.

   1234

   A Network Conditions rule using the 3G preset.

   1. Tool on/off
   2. Matcher: the host to slow down
   3. Preset menu
   4. Latency, download, upload, packet loss

   ×

   

2. Pick a preset from the Profile menu, or set the numbers by hand. Changing a value relabels the profile Custom.

   Preset	Latency	Download	Upload	Packet loss
   100% Loss	0 ms	0	0	100%
   Very Bad Network	500 ms	1000 kbps	1000 kbps	10%
   Edge	400 ms	240 kbps	200 kbps	0%
   3G	300 ms	780 kbps	330 kbps	0%
   DSL	50 ms	2000 kbps	256 kbps	0%
   LTE	50 ms	50000 kbps	10000 kbps	0%
   Wi-Fi	2 ms	40000 kbps	33000 kbps	0%

   Set Download or Upload to 0 for unlimited. Packet loss is the percentage of matching requests that fail as if the network dropped them.

Tip

Requests are delayed by half the latency on the way out and half on the way back, plus transfer time at the given speeds. So a 300 ms latency adds about 300 ms round trip, and a 1 MB body at 780 kbps adds roughly 10 seconds of download.

Slow everything down

To throttle all traffic rather than one host, set the rule’s matcher to *:

1. In the rule’s matcher, set the URL to * and leave Include subpaths on.

2. Choose a profile. Every request through the proxy is now shaped.

See the effect

1. Use the app and watch the Duration column in the traffic list climb. Throttled requests are tagged Network Conditions.

2. With Packet loss above 0, some requests fail outright — they show as failed in the list, which is how the app would see a dropped connection.

3. Open Insights (<kbd>⌥</kbd> <kbd>⌘</kbd> <kbd>I</kbd>) and the Timeline tab to see every request on one time axis, so you can spot the requests that now dominate the load time.

4. The Performance tab flags Slow responses, which helps you find what suffers most under the condition.

   12

   Performance findings. Slow requests rise to the top under a throttle.

   1. Filter by kind
   2. Slow requests, with the worst time

   ×

   

Clean up

1. Turn off Network Conditions with the switch in the Tools window, or untick it in the Tools menu, so traffic runs at full speed again.

2. Leave the rule in place to reuse it later, or select it and press the minus button to delete it.

Caution

It’s easy to forget a throttle is on and chase a “slow server” that is really the 3G preset. The status bar shows Network Conditions while the tool is active with a rule — click it to jump back to the Tools window.

Related

Network ConditionsLatency, speed, packet loss and the built-in presets.

TimelineEvery request on one time axis, with zoom.

PerformanceSlow, large, duplicate and N+1 findings.

Rules and matchingMatch one host, a path, or everything with wildcards.