iOS Simulator Skill for Claude Code
June 18, 2026 · View on GitHub
iOS Simulator Skill for Claude Code
Production-ready skill for building, testing, and automating iOS apps. 27 scripts optimized for both human developers and AI agents.
(If you'd prefer an MCP, XC-MCP)
Xcode Build + Simulator Automation
This skill covers both sides of iOS development:
- Xcode builds via
xcodebuild— compile, test, and parse results with progressive error disclosure - Simulator interaction via
xcrun simctlandidb— semantic UI navigation, accessibility testing, device lifecycle
If you only need Xcode build tooling without the simulator scripts, see the plugin version: xclaude-plugin
Installation
Via Plugin Marketplace (Recommended)
In Claude Code:
/plugin marketplace add conorluddy/ios-simulator-skill
/plugin install ios-simulator-skill@conorluddy
Via Git Clone
# Personal installation
git clone https://github.com/conorluddy/ios-simulator-skill.git ~/.claude/skills/ios-simulator-skill
# Project installation
git clone https://github.com/conorluddy/ios-simulator-skill.git .claude/skills/ios-simulator-skill
Restart Claude Code. The skill loads automatically.
Prerequisites
- macOS 12+
- Xcode Command Line Tools (
xcode-select --install) - Python 3
- IDB (optional, for interactive features:
brew tap facebook/fb && brew install idb-companion) - Pillow (optional, for visual diffs:
pip3 install pillow)
Features
Xcode Build with Progressive Disclosure
The build_and_test.py script wraps xcodebuild with token-efficient output. A build returns a single summary line with an xcresult ID:
Build: SUCCESS (0 errors, 3 warnings) [xcresult-20251018-143052]
Then drill into details on demand:
python scripts/build_and_test.py --get-errors xcresult-20251018-143052
python scripts/build_and_test.py --get-warnings xcresult-20251018-143052
python scripts/build_and_test.py --get-log xcresult-20251018-143052
This keeps agent conversations focused — no walls of build output unless you ask for them.
Simulator Navigation via Accessibility
Instead of fragile pixel-coordinate tapping, all navigation uses iOS accessibility APIs to find elements by meaning:
# Fragile — breaks if UI changes
idb ui tap 320 400
# Robust — finds by meaning
python scripts/navigator.py --find-text "Login" --tap
The accessibility tree gives structured data (element types, labels, frames, tap targets) at ~10 tokens default output vs 1,600-6,300 tokens for a screenshot. See AI-Accessible Apps for more on why accessibility-first navigation matters for AI agents.
Screenshot Token Optimization
When screenshots are needed (visual verification, bug reports, diffs), the skill automatically resizes and compresses them to minimize token cost. Default output across all 27 scripts is 3-5 lines — 96% reduction vs raw tool output.
| Task | Raw Tools | This Skill | Savings |
|---|---|---|---|
| Screen analysis | 200+ lines | 5 lines | 97.5% |
| Find & tap button | 100+ lines | 1 line | 99% |
| Login flow | 400+ lines | 15 lines | 96% |
All 27 Scripts
Every script supports --help and --json. See SKILL.md for the complete reference.
Build & Development
| Script | What it does | Key flags |
|---|---|---|
build_and_test.py | Build Xcode projects, run tests, parse xcresult bundles | --project, --scheme, --test, --get-errors, --get-warnings |
log_monitor.py | Real-time log monitoring with severity filtering | --app, --severity, --follow, --duration |
Device State
| Script | What it does | Key flags |
|---|---|---|
appearance.py | Switch dark mode, dynamic type, locale, region | --theme, --text-size, --locale, --region, --reset |
location.py | Simulate GPS coordinates and run built-in scenarios | --lat, --lng, --city, --gpx, --list-scenarios, --clear |
Navigation & Interaction
| Script | What it does | Key flags |
|---|---|---|
screen_mapper.py | Analyze current screen, list interactive elements | --verbose, --hints |
navigator.py | Find and interact with elements semantically | --find-text, --find-type, --find-id, --tap, --enter-text |
gesture.py | Swipes, scrolls, pinches, long press, pull to refresh | --swipe, --scroll, --pinch, --long-press, --refresh |
keyboard.py | Text input and hardware button control | --type, --key, --button, --clear, --dismiss |
app_launcher.py | Launch, terminate, install, deep link apps | --launch, --terminate, --install, --open-url, --list |
Testing & Analysis
| Script | What it does | Key flags |
|---|---|---|
accessibility_audit.py | WCAG compliance checking on current screen | --verbose, --output |
visual_diff.py | Compare two screenshots for visual changes | --threshold, --output, --details |
test_recorder.py | Automated test documentation with screenshots | --test-name, --output |
app_state_capture.py | Debugging snapshots (screenshot, hierarchy, logs) | --app-bundle-id, --output, --log-lines |
sim_health_check.sh | Verify environment (Xcode, simctl, IDB, Python) | — |
model_inspector.py | Inspect Core Data / SwiftData models from project files | --project-path, --raw, --show-versions |
container.py | Inspect app sandbox: list, cat, UserDefaults, Core Data, export | --ls, --cat, --userdefaults, --core-data-path, --export |
hang_watcher.py (HangBuster) | Record + summarise os_log hang events with progressive disclosure (session mode + raw NDJSON + legacy stream); auto-restart on stream death, automatic disk-cap cleanup | --start [--raw-capture --max-size-mb N --no-gzip], --stop, --get-details, --list-sessions, --diff, --budget-tokens, --auto-sample (legacy: --watch, --since) |
localization_audit.py | Audit .xcstrings catalogs for missing keys, unused keys, placeholder mismatches | --catalog, --source, --strict |
Permissions & Environment
| Script | What it does | Key flags |
|---|---|---|
clipboard.py | Copy text to simulator clipboard for paste testing | --copy, --test-name |
status_bar.py | Override status bar (time, battery, network) | --preset, --time, --battery-level, --clear |
push_notification.py | Send simulated push notifications | --bundle-id, --title, --body, --payload |
privacy_manager.py | Grant, revoke, reset app permissions (13 services) | --bundle-id, --grant, --revoke, --reset |
Device Lifecycle
| Script | What it does | Key flags |
|---|---|---|
simctl_boot.py | Boot simulators with readiness verification | --name, --wait-ready, --timeout, --all, --type |
simctl_shutdown.py | Gracefully shutdown simulators | --name, --verify, --all, --type |
simctl_create.py | Create simulators by device type and OS version | --device, --runtime, --list-devices |
simctl_delete.py | Delete simulators with safety confirmation | --name, --yes, --all, --old |
simctl_erase.py | Factory reset without deletion | --name, --verify, --all, --booted |
Configuration
Every operational limit — timeouts, output caps, polling intervals, cache size, post-action delays — is tunable via an IOS_SIM_* environment variable. Defaults are tuned for local development on Apple Silicon. Raise them on slow CI runners, large monorepos, or accessibility audits over complex screens. Lower them when you need faster failure or tighter token budgets.
There's a universal tradeoff to keep in mind:
- Higher caps / longer timeouts → fewer false failures, more complete diagnostics, more tokens consumed by AI agents and slower failures when something is genuinely broken.
- Lower caps / shorter timeouts → faster feedback, tighter token usage, risk of silently dropped errors or premature timeouts on legitimately slow operations.
Boot & lifecycle timeouts
How long to wait on xcrun simctl operations.
| Variable | Default | Tradeoff |
|---|---|---|
IOS_SIM_BOOT_TIMEOUT | 300 (s) | Wait for simulator readiness after boot. Lower → faster failure on broken sims. Higher → survives cold-start on slow CI runners (GitHub-hosted macOS can need 4–6 min). |
IOS_SIM_BOOT_SUBPROCESS_TIMEOUT | 60 (s) | Timeout for the simctl boot call itself (before readiness polling starts). Rarely needs changing; bump only if you see Boot command timed out on resource-starved CI. |
IOS_SIM_ERASE_TIMEOUT | 90 (s) | Wait for factory-reset verification. Larger simulators (lots of installed apps + data) can need more than the old 30s. |
IOS_SIM_POLL_INTERVAL | 0.5 (s) | How often to re-check boot/erase state. Lower → more responsive (more CPU). Higher → quieter on slow CI but adds latency to “ready” detection. |
IOS_SIM_STATE_SUBPROCESS_TIMEOUT | 15 (s) | Per-subprocess timeout in app_state_capture.py. Bump for apps with very large accessibility trees. |
Build & test output caps
build_and_test.py returns counts by default and full details via xcresult ID; these caps govern what's surfaced in human/JSON output before progressive disclosure kicks in.
| Variable | Default | Tradeoff |
|---|---|---|
IOS_SIM_BUILD_SUMMARY_CAP | 15 | Errors / failed tests in the default text summary. Lower → terser default output. Higher → less need to chase xcresult IDs for context. |
IOS_SIM_BUILD_VERBOSE_CAP | 100 | Errors / warnings in --verbose mode. Mostly relevant for monorepos or first builds with many fixable warnings. |
IOS_SIM_BUILD_JSON_CAP | 50 | Max errors / failed tests in --json output. Raise for CI dashboards that need exhaustive lists. |
IOS_SIM_BUILD_LOG_PREVIEW | 4000 (chars) | Chars of build log included in default output. Higher → more context for failures, more tokens. |
IOS_SIM_BUILD_TIMEOUT | 1800 (s) | Hard cap on a single xcodebuild build invocation. Default of 30 min covers most clean builds of large apps; raise for very large monorepos, lower to fail fast in CI when builds are expected to take seconds. Without this, a hung xcodebuild would block forever. |
IOS_SIM_TEST_TIMEOUT | 2700 (s) | Hard cap on xcodebuild test. Tests can take significantly longer than builds (45 min default) because of simulator boot + animation delays. |
IOS_SIM_INTROSPECT_TIMEOUT | 60 (s) | Timeout for xcodebuild -list and xcrun simctl list introspection calls. These should normally complete in <1s; 60s catches Xcode-toolchain hangs without disrupting cold-start. |
Log monitor output
log_monitor.py aggregates os_log output; these caps shape both the text summary and the structured JSON.
| Variable | Default | Tradeoff |
|---|---|---|
IOS_SIM_LOG_TEXT_SUMMARY | 15 | Errors / warnings shown in the text summary. The default surfaces enough for most debugging without flooding terminal output. |
IOS_SIM_LOG_LINE_MAX | 300 (chars) | Per-line truncation. Crash messages with full Swift symbol mangling can exceed 200 chars; raise if you see “…” cutting off the actionable bit. |
IOS_SIM_LOG_TAIL | 200 (lines) | Recent log lines shown in verbose mode and JSON sample_logs. Also used by xcode log excerpt. Lower for tighter context, higher for richer post-mortems. |
IOS_SIM_LOG_JSON_CAP | 100 | Max errors / warnings in JSON output. Raise if you're piping into a dashboard that needs the full picture. |
IOS_SIM_HANG_PREDICATE | (default) | Override the os_log predicate used by hang_watcher.py. The default catches RunningBoard watchdog kills, explicit "Hang detected" messages, and main-thread hang annotations. Hang events originate from system daemons (RunningBoard, SpringBoard, watchdog) — not the target app's process — so the predicate intentionally stays simulator-global. --bundle-id is applied post-parse against the event payload, never ANDed into the predicate. |
IOS_SIM_HANG_MIN_MS | 250 | HangBuster threshold: events below this duration never reach disk. |
IOS_SIM_HANG_SESSION_TTL_HOURS | 24 | HangBuster session prune age. Pruning runs on every --start. |
IOS_SIM_HANG_DEFAULT_TOP_N | 3 | Default top-N clusters in --stop L1 output. |
IOS_SIM_HANG_BUDGET_TOKENS | (unset) | Default token budget for --stop (picks L0/L1/L2 to fit). |
IOS_SIM_HANG_MAX_RESTARTS | 3 | HangBuster worker: bounded log stream respawn attempts on EOF/subprocess death before the session is marked crashed. Set to 0 to disable auto-restart. |
IOS_SIM_HANG_TOTAL_CAP_MB | 100 | HangBuster aggregate disk cap. When total session-state exceeds this on --start, oldest sessions are dropped first. Set to 0 to disable. |
UI navigation & screen mapping
These shape what AI agents see when exploring a screen. They're the biggest direct lever on token consumption per navigation step.
| Variable | Default | Tradeoff |
|---|---|---|
IOS_SIM_MAX_ELEMENTS | 25 | Tappable elements listed by navigator.py. Default is enough for most screens; raise to 100+ for dense Settings-style screens or audit workflows. High token impact at high values. |
IOS_SIM_SCREEN_BUTTONS_PREVIEW | 15 | Button names in screen_mapper.py summary. |
IOS_SIM_SCREEN_SECTION_ITEMS | 10 | Items per section in screen_mapper.py summary. |
IOS_SIM_APPS_PREVIEW | 30 | Installed apps listed by app_launcher.py before truncation. |
IOS_SIM_TAP_SETTLE_MS | 500 (ms) | Delay after a tap before reading new state. Lower → faster navigation on snappy apps. Higher → safer on apps with heavy animations or async loading; raises end-to-end test runtime linearly. |
IOS_SIM_RELAUNCH_DELAY_MS | 1000 (ms) | Delay between terminate and re-launch in app_launcher.py --restart. Raise if you see relaunches catching the previous process still tearing down. |
Accessibility audit
| Variable | Default | Tradeoff |
|---|---|---|
IOS_SIM_A11Y_TOP_ISSUES | 10 | Top issues surfaced per audit. Default of 3 in older versions was almost always too aggressive for real-world apps. Raise for first-pass audits, lower for regression checks. |
IOS_SIM_A11Y_LABEL_MAX | 80 (chars) | Max chars of AXLabel retained in audit output. Custom localized labels often exceed 30 chars; 80 catches almost all. |
Progressive disclosure cache
ProgressiveCache stores large outputs (build results, log dumps) keyed by short IDs so the default output stays minimal.
| Variable | Default | Tradeoff |
|---|---|---|
IOS_SIM_CACHE_TTL_HOURS | 1 | How long cache entries remain valid. Lower → fresher data on next retrieve, more re-runs. Higher → faster reruns in long CI pipelines, risk of stale results if simulator state changed. |
IOS_SIM_CACHE_MAX_ENTRIES | 500 | Hard cap; oldest entries (by mtime) are evicted on every save(). Prevents unbounded growth of ~/.ios-simulator-skill/cache/ in long-running environments. Raise only if you frequently need to retrieve entries older than ~500 saves. |
Examples
# Slow GitHub Actions macOS runner — give boot up to 10 minutes
IOS_SIM_BOOT_TIMEOUT=600 python scripts/simctl_boot.py --wait-ready
# Monorepo with hundreds of warnings — see them all in verbose mode
IOS_SIM_BUILD_VERBOSE_CAP=500 python scripts/build_and_test.py --verbose
# Complex Settings-style screen — return more tappable elements
IOS_SIM_MAX_ELEMENTS=100 python scripts/navigator.py --list-tappable
# Snappy app — cut tap-settle delay in half for faster E2E runs
IOS_SIM_TAP_SETTLE_MS=250 python scripts/navigator.py --find-text "Login" --tap
# Long CI pipeline — keep cache entries valid for the whole job
IOS_SIM_CACHE_TTL_HOURS=8 python scripts/build_and_test.py --project MyApp.xcodeproj
You can also export the vars once for the whole session:
export IOS_SIM_BOOT_TIMEOUT=600
export IOS_SIM_LOG_TAIL=500
export IOS_SIM_MAX_ELEMENTS=50
# … all subsequent scripts honor them
Parse errors fall back to the documented default with a warning on stderr — no scripts will crash on a malformed env var.
Evaluation
Tested using Claude Code evals:
| Condition | Pass Rate |
|---|---|
| With skill | 100% (3/3) |
| Without skill | 46% (~1.4/3) |
claude evals run evals/evals.json --skill ios-simulator-skill
License
MIT