Network Throttling

Throttle shapes the traffic flowing through Probe so you can see how your app behaves on a slow or flaky network. It works in two modes: a global profile that applies to every request, and a scoped rules list where each rule has its own URL matcher and shape parameters.

Throttling kicks in for everything that goes through Probe — desktop traffic and any phone or tablet using Probe as its proxy. There's no separate iOS/Android setting to maintain.

What gets shaped

Each profile is built from these knobs:

• Down speed (bytes/sec) — caps how fast the response reaches the client. Probe holds the response for its body size divided by this rate, so the average rate matches your value.
• Up speed (bytes/sec) — same idea, for the request body: Probe holds the request for its body size divided by this rate before forwarding it.
• Down delay / Up delay (ms) — extra latency added on each leg. Up delay is added before the request is forwarded; down delay is added before the response is surfaced. Together they simulate one round-trip's worth of RTT.
• DNS delay (ms) — extra delay applied at the start of every request, on top of the directional delays.
• Down loss / Up loss (%) — probability that a response (or request body) is dropped. At 100% loss the request hangs forever, simulating a dead network.

A value of 0 on any knob means "no effect" — Probe adds no delay for it and the traffic flows at full speed.

Built-in presets

Open the Throttle picker in the toolbar to pick a preset. The values match Apple's Network Link Conditioner reference profiles where applicable.

Preset	Down	Up	Delay (down/up)	Loss
Off	uncapped	uncapped	0 / 0	0%
DSL	2 Mbps	256 kbps	5 / 5 ms	0%
3G	780 kbps	330 kbps	100 / 100 ms	0%
LTE	50 Mbps	10 Mbps	50 / 65 ms	0%
High Latency DNS	uncapped	uncapped	0 / 0 ms (+ 3000 ms DNS)	0%
Very Bad Network	1 Mbps	1 Mbps	500 / 500 ms	10% / 10%
100% Loss	uncapped	uncapped	0 / 0	100% / 100%

You can save your own custom profiles next to the built-ins if you frequently reach for a specific shape.

Global mode

Click the throttle icon in the toolbar and pick a preset (or open Custom Profiles… to dial your own). The change applies immediately to every new connection — both desktop and any device using Probe as its proxy. Pick Off to disable throttling.

The icon highlights when a profile other than Off is active so you don't forget you're shaping traffic.

Scoped rules: throttle only what matters

The global profile is a blunt instrument — it touches every request. The scoped rules list lets you apply different shapes to different URLs, leaving everything else alone.

Each rule has:

• a matcher — host, URL glob, or app/process name,
• a profile — the same set of knobs as the global profile (down/up bps, delays, loss),
• an enabled toggle.

Probe evaluates the rules in order; the first match wins, and the matched profile overrides the global profile for that request. Once a rule is chosen for a request, its shape is locked in for both the request and response leg, even if you edit the rules list mid-flight.

The rule editor

Add or edit a rule from the throttle rules list. On macOS and Windows, the editor opens as a native child window — a separate OS window with its own title bar — so you can leave it floating while you watch live traffic in the main Probe window and tweak the rule's pattern or shape on the fly. Quick-create paths (e.g. right-click a log row → Tools → Throttle) use the same surface; they pre-fill the request's host, path and query and pick the URL glob matcher, so the new rule matches that request right away.

URL-shape note

Throttle URL globs are matched with the default port (:443 for HTTPS, :80 for HTTP) removed, like Map Local, Map Remote, Breakpoints and Scripting rules. A pattern without a scheme (api.example.com/v1/upload/*) is compared with the URL minus its scheme, so it matches HTTP and HTTPS; a pattern with a scheme (https://…) matches only that scheme. The scheme and host ignore case (API.Example.com matches api.example.com); the path and query are case-sensitive.

Worked example: slow uploads only

You want to verify your upload progress UI on a real LTE connection — but only for upload calls. Other traffic should flow at full speed.

1. Set the global profile to Off.
2. Open the throttle rules list and add:
   • Matcher: URL glob **/v1/upload/*
   • Profile: Down 50 Mbps, Up 1 Mbps, delay 50 / 65 ms
3. Save and enable the rule.

Now uploads crawl at 1 Mbps and you can watch your progress bar do real work, while every other request still flies.

Related

• Breakpoints — pause traffic instead of slowing it.
• Map Local — combine a fake response with a delay to test loading states.