Lagsmith

Network testing for iOS and macOS developers

Network Link Conditioner for a single app

Network Link Conditioner slows down your whole Mac: Xcode, Slack, and the agent writing your code. Lagsmith puts only the app you pick on 3G, even one app on one simulator.

Download for Mac How it compares

Free download. 14-day Pro trial, no account. macOS 13 Ventura or later.

Your agent can test on 3G without crawling along with the app

Lagsmith has an MCP server. Ask Claude Code to test checkout on a bad network and it puts just your app on 3G, runs the UI tests, and reads the requests that failed.

Set up the MCP server

> Test checkout on 3G with the payments API returning 503s.
lagsmith - set_network (MCP)(app: "com.pantryhq.Pantry", preset: "3G")
{"ok": true, "preset": "3G", "conditions": {"down": 780, "latency": 200}}
lagsmith - fail_endpoint (MCP)(pattern: "api.pantryhq.app/v1/payments", kind: "status", value: 503)
{"ok": true}
Bash(xcodebuild test -scheme PantryUITests -only-testing:PantryUITests/CheckoutTests)
✓ testCartLoads (4.8 s)✗ testPlaceOrder (30.0 s): Failed to find "Order confirmed"
Found it: when payments fails, checkout spins forever because there’s no error state. Want me to add one with a "Try again" button and rerun the tests?
Illustrative Claude Code session using Lagsmith’s MCP server. Your agent stays at full speed; only Pantry is on 3G.
Pantry iPhone 17 Pro · iOS 26
Very Bad Network
  1. POST200 OK1.4 s /v1/cart
  2. GET200 OK2.8 s /v1/recipes?page=2
  3. POSTTimed out30 s /v1/payments
  4. GET200 OK3.1 s /v1/images/7f3a…c91.jpg
  5. GET304640 ms /v1/user/profile
  6. POST2021.9 s /v1/events
  7. GET200 OK912 ms /v1/pantry/items
46 requests · 1 failed · click to inspect

A small window next to the simulator

The mini monitor floats beside the app you’re testing and lists its requests as they happen, so you can see the time-out while you tap around. Click it to open the inspector.

Request monitoring

See every request, down to the photo

Headers, bodies and timing for every request a simulator app makes, with no certificate to install. JSON opens as a tree, and hovering an image URL shows the image.

PantryiOS Simulator · iPhone 17 Pro
PathMethodStatusTimeSize
/v1/sessionPOST 200 OK 1.3 s412 bytes
/v1/user/profileGET 304 Not Modified 640 ms—
/v1/pantry/itemsGET 200 OK 912 ms8 KB
/v1/recipes?page=2GET 200 OK 2.8 s25 KB
/r/412.jpgGET 200 OK 3.1 s64 KB
/r/387.jpgGET 200 OK 2.6 s58 KB
/v1/cartPOST 200 OK 1.4 s1 KB
/v1/paymentsPOST Timed out 30 s—
/v1/eventsPOST 202 Accepted 1.9 s—
/v1/recommendationsGET 200 OK 2.2 s6 KB
/r/355.jpgGET 200 OK 2.9 s61 KB
GET https://api.pantryhq.app/v1/recipes?page=2 200 OK
2.8 s · 25 KB · 11:46:36 AM
KeyValue
⌄recipes [ 24 items ]
⌄0 { 7 keys }
id 412
title "Lemon orzo with peas"
minutes 25
servings 4
imageUrl "https://cdn.pantryhq.app/r/412.jpg"
›tags [ 3 items ]
saved true
›1 { 7 keys }
›2 { 7 keys }
›3 { 7 keys }
›4 { 7 keys }
›5 { 7 keys }
›6 { 7 keys }
nextPage "/v1/recipes?page=3"

What else it does

Throttle one app
3G, Edge, LTE, or your own bandwidth, latency and packet loss.
Airplane Mode for one app
Plus time-outs, refused and dropped connections.
Fail or mock one endpoint
Make /v1/payments return a 503 and leave the rest of the API alone.
Automation
Set the network from XCUITest, the command line or a lagsmith:// link.
MCP server
For Claude Code, Cursor, Codex and anything else that speaks MCP.
HAR export
Hand a recording of the bad session to whoever owns the backend.

Compared with Network Link Conditioner

Apple’s Network Link ConditionerLagsmith
What it slowsThe whole MacOnly the apps you pick
Your AI agentSlowed down too, and can’t control itFull speed, and drives Lagsmith over MCP
iOS SimulatorEvery app at onceOne app, even on one device
FailuresPacket loss onlyAirplane Mode, time-outs, dropped and refused connections
Fail or mock one endpoint✕✓
See requests✕✓
UI tests and command line✕✓

Read the full comparison

Pricing

Free

  • Watch any app
  • See its last 50 requests and its connections
  • Slow it down with the Edge preset

Pro

$59 $39 launch price

Launch price for early supporters. Until November 30, then $59. One-time purchase with a year of updates.

  • 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

See pricing

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.

Download for Mac

Free download with a 14-day Pro trial. No account, no card. macOS 13 Ventura or later.