/run-simulator

name: run-simulator
description: Build, install, launch, and screenshot an iOS app in the Simulator to verify a change visually. Use when the user wants to run the app, see a change live, screenshot the running app, or confirm a UI fix actually works (not just that it compiles).
allowed-tools: [Bash, Read, Glob]
last_verified: 2026-11-04
review_by: 2027-06-22

Run in Simulator

Launches the **actual app** in the iOS Simulator and drives it far enough to see what a user would see. Building proves the code compiles; this skill proves it *runs*. The payoff is a screenshot of the live app that you read back to confirm the change — a blank or crashed frame is a failure, not a pass.

> **The rule:** navigate with the accessibility tree; screenshots verify > outcomes, never locate tap targets. Text is cheap and exact; every image you > Read stays in context for the rest of the session.

This skill is generic. Nothing about a specific app is hardcoded — the scheme, simulator, product path, and bundle id are all discovered at runtime.

When This Skill Activates

Use this skill when the user:

• Asks to "run", "launch", or "open" the app in the simulator
• Wants to *see* a change working, not just compile it
• Asks for a screenshot of the running app
• Wants to verify a UI fix visually before committing or pushing
• Says "does this actually work?" about a view/flow they just changed

Do **not** use it for unit/UI test runs (`xcodebuild test`) — that's a different goal. This is about meeting the app as a user would.

Process

Run the steps in order. Each step's output feeds the next, so don't hardcode values a previous step can discover.

1. Discover the project and scheme

Prefer a workspace over a bare project when both exist (CocoaPods/SPM setups often require the workspace):

# Find the container
ls *.xcworkspace 2>/dev/null || ls *.xcodeproj 2>/dev/null

# List schemes (use -workspace X.xcworkspace OR -project X.xcodeproj)
xcodebuild -list -project <App>.xcodeproj 2>/dev/null

Pick the app scheme (usually matches the app name). If several schemes look plausible and none clearly matches, **ask the user** which to run rather than guessing.

2. Pick a simulator destination

**Never hardcode a device name** — the named device may not exist on this Mac (e.g. assuming "iPhone 16" when only "iPhone 17 Pro" is installed fails with *"Unable to find a device matching the provided destination specifier"*). List what's actually available and prefer one already booted:

# Already-booted sim, if any (fastest — skip the boot wait)
xcrun simctl list devices booted

# Otherwise, available iPhones to choose from
xcrun simctl list devices available | grep -i iphone

Choose a booted device if present; otherwise pick a recent iPhone from the available list and remember its name for the destination string.

3. Build for the simulator

xcodebuild build \
  -project <App>.xcodeproj \
  -scheme <Scheme> \
  -destination 'platform=iOS Simulator,name=<SimName>' \
  2>&1 | tail -5

• Read the tail for `** BUILD SUCCEEDED **`. Note that `-quiet` *suppresses*

that success line, so either drop `-quiet` for the confirming run or grep for `error:` explicitly.

• On failure, surface the `error:` lines — don't proceed to install a stale or

nonexistent build.

4. Resolve the built `.app` and its bundle id

Don't guess the DerivedData path — ask the build system for it:

# Product directory + name from the resolved build settings
eval $(xcodebuild -project <App>.xcodeproj -scheme <Scheme> \
  -destination 'platform=iOS Simulator,name=<SimName>' \
  -showBuildSettings 2>/dev/null \
  | awk -F' = ' '/ TARGET_BUILD_DIR =/{print "DIR=\""$2"\""} / FULL_PRODUCT_NAME =/{print "NAME=\""$2"\""}')
APP="$DIR/$NAME"
echo "APP: $APP"

# Bundle id straight from the built Info.plist
BID=$(/usr/libexec/PlistBuddy -c "Print :CFBundleIdentifier" "$APP/Info.plist")
echo "Bundle id: $BID"

5. Boot, install, launch

SIM="<SimName>"
xcrun simctl boot "$SIM" 2>/dev/null   # no-op if already booted
open -a Simulator                      # bring the window forward
xcrun simctl bootstatus "$SIM" -b      # block until fully booted

xcrun simctl install "$SIM" "$APP"
xcrun simctl launch "$SIM" "$BID"

`simctl launch` prints `<bundleid>: <pid>` on success. A non-zero exit or an error string here means the app failed to start — investigate before screenshotting.

6. Navigate to the screen (if the change is behind navigation)

`xcrun simctl` **cannot tap** — `simctl io` has no tap operation (only `enumerate`, `poll`, `recordVideo`, `screenshot`). Navigation needs a tool that reads the accessibility tree. Pick the first that works:

**a. Deep link** — if the app has a URL route to the screen, it's the cheapest path: `xcrun simctl openurl "$SIM" "<scheme>://<path>"`.

**b. AXe** (`command -v axe`; install: `brew install cameroncooke/axe/axe`). AXe needs the simulator's UDID:

UDID=$(xcrun simctl list devices booted -j \
  | jq -r --arg n "$SIM" '.devices[][] | select(.name==$n or .udid==$n) | .udid' | head -1)

# Compact element list: type, label, id, centre point. ~2 KB per screen.
# NEVER Read raw `axe describe-ui` output — it is ~280 KB (≈70k tokens) for
# one screen, far more than a screenshot.
UI_FILTER='[.. | objects | select(has("type") and (.AXLabel // .AXUniqueId // "") != ""
  and .type != "Application" and .type != "Group")
  | {t: .type, l: .AXLabel, id: .AXUniqueId, v: .AXValue,
     xy: [(.frame.x + .frame.width/2 | floor), (.frame.y + .frame.height/2 | floor)]}
  | with_entries(select(.value != null))]'
axe describe-ui --udid "$UDID" | jq -c "$UI_FILTER" | jq -c '.[]'

Tap the target, most specific first:

axe tap --id "<AXUniqueId>" --udid "$UDID"                              # 1. accessibilityIdentifier
axe tap --label "<AXLabel>" --element-type Button --wait-timeout 5 --udid "$UDID"  # 2. label (+ type)
axe tap -x <x> -y <