LagsmithNetwork testing for iOS and macOS developers
Slow down one app, not your whole Mac
Lagsmith slows down and breaks the network for one app at a time, including apps in the iOS Simulator. Your browser, Slack, Xcode and your AI agent stay at full speed.
Free, with a 14-day Pro trial. No account. macOS 13 Ventura or later, Apple silicon and Intel.
Everything you need to test bad networks
Throttle one app
Pick a running Mac app or an app in a booted iOS Simulator. Use Edge, 3G, DSL, LTE, WiFi or Very Bad Network, or set your own bandwidth, latency, jitter and packet loss. Every other app stays at full speed.
Break it on purpose
Airplane Mode for one app, refused connections, time-outs, dropped connections and outages that come and go. In the simulator, NWPathMonitor and SCNetworkReachability report no network, like a real device.
Fail or mock one endpoint
Make a single API endpoint go offline, time out, return an HTTP status or respond slowly, or mock it with a made-up response starting from the real one. The rest of the app keeps working.
See every request
Method, URL, status, timing, headers, bodies, a JSON tree and image previews for simulator apps. Search with filters like status:4xx or -host:cdn, and export as HAR.
Automate it
Set the network from an XCTest UI test before launching the app, or use the ivar command line tool, lagsmith:// links or the local HTTP API.
Let your AI agent drive
The built-in MCP server lets Claude Code, Cursor, Codex and others slow down the app under test, read its requests and mock endpoints, without slowing down the agent itself.
Compared with Apple’s Network Link Conditioner
Network Link Conditioner, per app
Network Link Conditioner is a good free tool from Apple. Lagsmith is what you reach for when you need it per app, need real failures, or need to see what’s happening.
| 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 |
Read the full comparison · How to install and use Network Link Conditioner
For AI coding agents
Run your end-to-end tests on 3G without slowing down your agent
Throttle the whole Mac and your AI agent slows down with it. Lagsmith’s built-in MCP server lets Claude Code, Cursor, Codex, Claude Desktop and Windsurf list simulators and apps, set and reset one app’s network, relaunch it with monitoring, read its requests, and fail or mock endpoints.
Free to start, Pro when you need it
Free
- Watch any app
- See its last 50 requests and its connections
- Slow it down with the Edge preset
Pro
$39 one-time
One-time purchase. Includes a year of updates, and your version keeps working forever.
- Every preset per app, custom presets and profiles
- Airplane Mode and failure modes
- Fail and mock endpoints
- UI tests, command line and MCP for AI agents
- Unlimited history, search filters, HAR export, mini monitor
Every install starts with a 14-day Pro trial. See pricing
Frequently asked questions
How is Lagsmith different from Apple’s Network Link Conditioner?
Network Link Conditioner slows down the whole Mac. Lagsmith slows down only the apps you pick, including individual apps in the iOS Simulator, and adds failure modes, request monitoring and automation. See the full comparison.
Does it work with the iOS Simulator?
Yes. Pick an app in a booted simulator and Lagsmith slows down or breaks only that app, even on one simulator device while another runs normally.
Do I need to install a certificate or change proxy settings?
No. Lagsmith sees the requests of simulator apps without certificates or proxy settings, and everything stays on your Mac.
What does Lagsmith install?
A network extension. macOS asks you to allow it once in System Settings. See getting started.
Which Macs does it run on?
macOS 13 Ventura or later, on Apple silicon and Intel.
Is there a free version?
Yes. Every install starts with a 14-day Pro trial with no account or card. After that, the free version keeps working: watch any app, see its last 50 requests and its connections, and slow it down with the Edge preset.
Does Lagsmith collect any data?
No. Everything runs locally, there is no account, and the app has no analytics.
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.