limrun-ios-simulator

Limrun iOS Simulator

Interact with an app running on a Limrun cloud iOS simulator, from any environment (Linux, Windows, macOS, VM, container). This skill is build-agnostic: it assumes the app was already built and installed by a build skill (limrun-xcode-bazel for Bazel, limrun-xcode for xcodebuild). Keep build concerns in those skills; this one is about driving the running simulator.

Never use local Xcode, local simulators, or local macOS tools.

Auth and CLI

Install if needed: npm install --global lim. Auth is lim login or LIM_API_KEY (it may be set outside the project, so don't ask for it just because it's missing from .env or the shell). The CLI is the source of truth: the commands in this skill are verified, but if a flag errors or you need one not shown here, check lim ios <subcommand> --help instead of guessing.

Installing an app bundle

You can either use Limrun remote Bazel or Xcode services to build the app bundle and have it installed to the simulator automatically or you can sync a pre-built local .ipa file or .app folder to the simulator. The main requirement is that it must be built for simulator.

Build and install

A build skill usually attaches the simulator for you (lim xcode rbe --ios, or lim xcode build . then attach). Check what's already there:

lim xcode get      # is a simulator attached to the current build target?
lim ios list       # all running iOS instances

If none is attached, create one. It installs the last build immediately, so you don't need to rebuild:

lim ios create --attach

If the create (or lim xcode rbe --ios) output includes a signed stream URL, share it with the user as a Markdown link, like [Live simulator](<signed-stream-url>). If you have a browser the user can see, open the URL there and tell them. Otherwise pass --no-open to create: it skips opening the URL locally and still prints it for sharing.

lim xcode get prints a Limrun console URL instead. It opens the same live view but requires a console login, so prefer the signed stream URL for sharing. If the console URL is all you have, share it and mention it needs login.

Install app from local

Create a new simulator:

Share the signed stream URL with the user as a Markdown link, like [Live simulator](<signed-stream-url>). If you have a browser the user can see, open the URL there and tell them.

You can then run the following command to upload a bundle from local:

You can run the same command every time you need to install a new version of the bundle. It will patch with the difference and reload it in the simulator.

Targeting the right instance

Most lim ios commands default to the last created instance and resolve the "current" one from the git repo / worktree of your cwd. So even when a simulator is attached and lim xcode get shows it, a lim ios command can still report No instance ID provided and no recent ios instance found, because your cwd isn't the git worktree where the instance was created (or isn't a git repo at all). This bites most often right after lim xcode rbe --ios in a fresh project.

The reliable recipe when that happens:

lim xcode get is the dependable source for the attached simulator's ID (lim ios list also works). Once you have it, pass --id <ios-instance-id> to all lim ios calls for the rest of the session (screenshot, tap, type, element-tree, record). Alternatively, git init the project so the workspace resolves on its own. When controlling multiple instances, always pass --id.

Reaching services on the local machine

Destination tunnels let an iPhone simulator app keep calling its normal destinations while the CLI dials them from the machine running lim. Select exact localhost:port or literal IP:port destinations, or domains that only your machine or VPN can reach:

Use the app's normal URLs, such as http://localhost:3000. Declaring localhost:3000 also captures loopback forms such as 127.0.0.1:3000 and [::1]:3000, plus [::ffff:127.0.0.1]:3000. Domain selectors (exact api.corp.example or label-bound wildcard "*.staging.example") are intercepted on the simulator and dialed from your machine whether or not the name resolves on public DNS, so your DNS and VPN apply and TLS stays end to end. Apps that resolve DNS themselves over HTTPS bypass domain interception. A tunnel carries TCP only: up to ten exact selectors and 64 domain selectors, ports 1-65535 except 53; CIDRs and UDP are not supported. Start the tunnel before launching the app: connections opened earlier keep their original route.

One instance accepts one active destination tunnel, and its selector set is immutable. To add or remove a destination, stop the tunnel and start it again with the complete selector list:

If the simulator attempts a route while its local service is stopped, the tunnel remains active and reports connection_refused; restart the service without recreating the simulator or tunnel.

Launching the app

The build skills reinstall and relaunch the app after every successful build, so you usually don't need to launch it yourself. When the app is closed (a fresh attach to an old build, or after a terminate), launch it by bundle ID:

If you don't know the bundle ID, run lim ios list-apps.

The lim ios launch-app will stream the logs from the app in realtime for you to debug. If you'd like to launch and forget, you can use --detach flag.

Testing changes

When simulator interaction is part of the task, test new or changed functionality with the interaction commands after each build. Focus on what changed, plus a quick smoke test of core flows. Start by reading the element tree to see what's on screen before acting:

Interacting with the app

Prefer tapping by accessibility id, then by label, then coordinates as a last resort:

tap-element taps with a real synthesized touch. Elements the accessibility tree can see are scrolled into view automatically. A selector that matches nothing in the tree fails in about a second; iOS creates list rows lazily, so a below-the-fold row often isn't in the tree at all. For those, pass --scroll-search: the CLI pages the screen (a few pages down, then up) retrying the tap until the row materializes, which can take ~10s. Pass --activate ax to use an accessibility press instead of a touch (no scrolling, works on elements without a usable frame).

Toolbar / nav-bar items usually can't be tapped by id. SwiftUI collapses toolbar children into a single nav-bar group, and those items report AXUniqueId: null even when you set .accessibilityIdentifier(...) (regular content Buttons do expose it). So tap-element --ax-unique-id finds nothing for a nav-bar button. Set an .accessibilityLabel / .accessibilityIdentifier anyway for documentation, but to actually tap it, read its AXFrame from the element tree and tap the center by coordinate:

For text input, focus a field first (tap it), then type:

type presses real keys, so text delegates fire and the field's own keyboard behavior applies (a default text field autocapitalizes the first letter, for example). To set a value verbatim with no keyboard behavior, use set-text:

For scrolling and drags:

After every interaction, re-run element-tree to confirm the UI transitioned. No sleep is needed between a tap and element-tree; the tap blocks until done.

Chain multiple actions with precise timing via perform:

Run lim ios perform --help for the full action grammar.

Screenshots and video

Screenshot takes a positional path (not -o):

Use the element tree for functional assertions (element existence, labels, state changes) and screenshots only for visual properties. For anything involving motion (animations, gameplay, streaming UI), prefer video:

For UI changes, include a demo video in the pull request so the user can see it.

App container files

List an app's data container before pulling a file so you use the exact path the app created. Keep the same --bundle-id and --container-type flags for list, pull, push, and delete:

lim ios ls defaults to the staging-folder root. With --bundle-id, it defaults to the app bundle (--container-type app); use data for the app's writable Documents, Library, and tmp directories. Paths in ls output are relative to the selected root and can be copied directly into the other file commands.

Simulate the camera with a video

For camera-driven flows (QR-code scanning, document capture, video calls), play a local video file as the simulator's camera. The app sees the frames through its normal capture pipeline:

Any AVFoundation-decodable file works (H.264/HEVC in .mp4/.mov). Use --no-loop when the app must observe the end of the clip exactly once (the feed freezes on the last frame rather than stalling).

Preview URL for humans

Upload the .ipa file directly or targz archive of the .app folder to Limrun Asset Storage and return a preview URL for the user to open it and test the app manually in the browser.

Here is how to upload it:

Once the command finishes, you can give the following URL to the user to click to see a simulator where this bundle is pre-installed.

Cleanup

When the work is completed, you can delete the iOS simulator.

Gotchas

• Instance resolution can miss in a non-git dir. See "Targeting the right instance" above; pass --id when in doubt.
• element-tree can be large. Pipe through grep / jq to extract what you need rather than dumping the whole tree into context.
• type / perform typeText may not drive SwiftUI (or React Native) state. Automated text injection sets the field's value through accessibility, which does not always fire a SwiftUI @Binding / onChange the way a real keystroke does. Symptom: the text appears in the field (and in element-tree), but reactive UI tied to it doesn't update (a send button stays disabled, a character counter doesn't move) and submit handlers see empty state. A real keyboard on the live stream works. When automating, drive submit through a tappable control (a button, a suggestion chip) rather than relying on text bound to reactive state, or have the app expose a test affordance.
• Toolbar / nav-bar items aren't tappable by id. See "Interacting with the app" above: read the AXFrame from element-tree and tap by coordinate.
• Bundle ID discovery. If you don't know the bundle ID, run lim ios list-apps after a successful install.
• Build errors are the build skill's job. If the app isn't installing, the failure is upstream; go back to limrun-xcode-bazel / limrun-xcode.