LagsmithA Network Link Conditioner alternative that works per app
Apple’s Network Link Conditioner slows down your whole Mac. Lagsmith is a Network Link Conditioner alternative that slows down only the app you are testing, including a single app in the iOS Simulator, and adds the failures and visibility that bad-network testing needs.
Side by side
| Apple’s Network Link Conditioner | Lagsmith | |
|---|---|---|
| What it slows | The whole Mac: your browser, Slack, Xcode downloads, your AI agent, everything | Only the apps you choose |
| iOS Simulator | Throttles the whole Mac, so every simulator app and everything else too | Per simulator app, even per simulator device |
| How you get it | Separate "Additional Tools for Xcode" download from Apple’s developer site, installed as a System Settings pane | A normal Mac app with a menu bar icon |
| Failures | Packet loss and bandwidth/latency only | Airplane Mode, refused connections, time-outs, dropped connections, outages that come and go |
| Failing one endpoint | No | Fail, delay or mock a single API endpoint while the rest works |
| Seeing requests | No | Every request of a simulator app: URL, headers, bodies, timing, JSON tree, image previews |
| Automation | No | UI test helper, command line, URL scheme, local HTTP API, MCP server for AI agents |
When Network Link Conditioner is enough
Network Link Conditioner is a good, free tool from Apple. It is the right choice when:
- You want the whole Mac to be slow, for example to feel how a website loads on 3G.
- You are testing on a physical iPhone or iPad, where it is built into Settings › Developer.
- Bandwidth, latency and packet loss are all you need, and you don’t mind everything else slowing down while you test.
When you need Lagsmith
You want to keep working while you test
With Network Link Conditioner on, your browser, Slack, Xcode downloads and your AI coding agent all crawl. Lagsmith throttles only the app you pick, so everything else stays at full speed.
You test in the iOS Simulator
Lagsmith throttles one simulator app, or even one app on one simulator device while the same app on another device runs normally. How to throttle the iOS Simulator.
You need failures, not just slowness
Airplane Mode for one app, refused connections, time-outs, dropped connections and outages that come and go. In the simulator, Airplane Mode behaves like a real device: requests fail with “The Internet connection appears to be offline” and NWPathMonitor reports no network. Airplane Mode in the iOS Simulator.
You need to break one endpoint
Fail, delay or mock a single API endpoint while the rest of the app works. Mock an API in the iOS Simulator.
You want to see what the app is doing
Lagsmith shows every request of a simulator app with headers, bodies, timing, a JSON tree and image previews, with no certificates or proxy settings.
You want it in tests and CI
Set the network from an XCTest UI test, the ivar command line tool, lagsmith:// links, a local HTTP API or the MCP server for AI agents. Automation docs.
Moving from Network Link Conditioner
Your Network Link Conditioner presets are all here, by the same names: Edge, 3G, DSL, LTE, WiFi, Very Bad Network and 100% Loss. Pick one for an app, or start from one and save your own custom preset with different bandwidth, latency, jitter or packet loss.
- Turn Network Link Conditioner off in System Settings so it doesn’t slow down the whole Mac.
- Download Lagsmith and allow its network extension when macOS asks. Getting started.
- Click the Lagsmith menu bar icon, pick the app you are testing, and choose the same preset you used before.
Frequently asked questions
Is Lagsmith a replacement for Network Link Conditioner?
For per-app testing, yes. Lagsmith has the same presets by the same names, applied to one app instead of the whole Mac. If you want to slow down the entire Mac on purpose, Network Link Conditioner still does that well.
Can I keep Network Link Conditioner installed?
Yes. They are separate tools. Just remember that if Network Link Conditioner is on, it slows down everything, including apps Lagsmith leaves alone.
Can Network Link Conditioner throttle only the iOS Simulator?
No. Network Link Conditioner on the Mac applies to the whole Mac, so it slows down every simulator app and every other app at the same time. Lagsmith can throttle a single app in a single simulator device.
Does Lagsmith work on a real iPhone?
Lagsmith works on Mac apps and apps in the iOS Simulator. On a physical iPhone, use Network Link Conditioner in Settings › Developer.
Slow down one app, not your whole Mac
Free to download, with a 14-day Pro trial. No account, no card. Requires macOS 13 Ventura or later.