eas-simulator

EAS Simulator

EAS service - costs apply. EAS Simulator runs on Expo Application Services cloud infrastructure, a paid product with free-tier limits; remote simulator sessions use your plan's compute allowance. See https://expo.dev/pricing.

EAS Simulator runs a remote iOS simulator or Android emulator on EAS infrastructure that you drive from your machine — from the CLI, from an AI agent (via agent-device), and from a browser preview. It's the unlock for environments that can't run a simulator locally (Linux boxes, cloud/background agents like Cursor Cloud), and for letting an agent verify a change on a real device instead of only reasoning about code.

The simulator:* commands are experimental and hidden, and need a recent eas-cli (≥ 20.3.0 as of writing) — which is why this skill runs everything via npx --yes eas-cli@latest. Flags and verbs may change; if a command fails, <cmd> --help is authoritative.

When to use

The frontmatter description carries the trigger phrases. In short: use this to get a user's app onto a cloud simulator and interact with it — especially from a Mac-less or cloud/sandbox agent. Not for local sims (expo run:ios, Xcode, Android Studio), store builds/signing (that's EAS Build), or physical devices. For the macOS case, see Cloud vs local next.

Cloud vs local: decide this first

• Non-macOS (Linux / CI / cloud sandbox like Cursor Cloud, detect via uname -s ≠ Darwin): the only way to get a sim — just proceed.
• macOS: local sims exist and a cloud session costs money + latency, so ask first ("a remote cloud sim — to share a live preview, offload, or test an iOS version you lack — or just run locally?") unless the user explicitly said cloud/remote/shareable.
• Always honor an explicit choice; for "run it locally" hand off to expo run:ios / Xcode.

# Programmatic detection — run this to decide before doing anything else:
if [ "$(uname -s)" != "Darwin" ] || ! xcrun --find simctl &>/dev/null 2>&1; then
  echo "no local sim — proceed with EAS Simulator"

Prerequisites

• Run every eas command via npx --yes eas-cli@latest … — guarantees a CLI new enough to have simulator:* (a global eas is often too old), and --yes skips npx's prompt. (Bare eas is fine if eas --version is current.)
• Authenticated. Interactive machine → npx --yes eas-cli@latest login. Cloud sandbox / CI / headless agent has no browser login — set EXPO_TOKEN (expo.dev → Account → Access Tokens) in the env instead. Verify either way with npx --yes eas-cli@latest whoami.
• Run from an Expo project directory. A fresh app needs one-time setup: npx --yes eas-cli@latest init to create/link the project (when there's no projectId), and set ios.bundleIdentifier in app config if it's missing — a fresh create-expo-app often has none, and prebuild/eas build need it (they prompt or fail without it; e.g. dev.<owner>.<slug>). Read current config with npx expo config --json (it may live in app.config.js). The first Mode-C run is slow (native build); later runs reuse it.
• A controller to drive the device. This skill uses agent-device (open source, MIT), run on demand via npx agent-device@latest — nothing globally installed. argent is an alternative (--type argent in simulator:start); see references/controllers.md.
• .env.eas-simulator is written/managed by eas-cli (not this skill): it holds the session id (EAS_SIMULATOR_SESSION_ID) + the daemon URL/token, so get/stop/exec default to that session (usually omit --id; pass --id <id> to target another). It carries a token → keep it gitignored (eas-cli marks it "do not commit" but may not add the ignore rule, and a fresh app's .gitignore won't cover it — add .env.eas-simulator if missing).
• --max-duration-minutes is paid-plan only; otherwise a default applies.
• The command blocks assume a POSIX shell (bash/zsh) — printf, lsof, $(seq …) loops won't run in cmd/PowerShell. On Windows, run them in WSL or Git Bash, or translate as you go (the eas-cli/agent-device invocations themselves are cross-platform).

The core loop (always the same)

A session is: start → (install your app) → drive → stop. eas-cli owns the session; the device verbs (open/tap/screenshot) come from the controller, which npx --yes eas-cli@latest simulator:exec runs for you with the session's connection env loaded.

To watch it live, hand the user the webPreviewUrl that start prints (an --type agent-device iOS session runs serve-sim alongside the daemon, so it emits one — agent control and a browser preview in one session; Android has no preview, and --type serve-sim is preview-only). This URL is for the user's browser — you cannot open it for them, and it must never touch the sim:

• "Open it here" (Cursor/VS Code) → print the URL on its own line and tell the user to open Simple Browser (Cmd/Ctrl+Shift+P → "Simple Browser: Show") and paste it. Then stop: do not shell out to a system browser or a Cursor/VS Code URL handler, and do not ask "did a tab appear?" — you can't confirm it, the handoff is done.
• Never open the webPreviewUrl on the sim. It's a browser preview, not a deep link and not an agent-device open argument; routing it to the device renders a browser-in-a-browser (a real past failure).
• Headless agent (no display) → just return the URL as the deliverable.
• Keeping it alive for the user to drive → bound it: start with --max-duration-minutes N so it auto-stops; tell them it bills until stopped and when it auto-stops; offer to reopen/extend when it ends. (This is the one case where "stop right away" doesn't apply; one-shot screenshot/get runs still stop immediately.)

start also prints a job-run URL.

Commands at a glance

Running the user's app — pick a mode

The remote sim boots blank — no Expo Go, no apps. Install a build, then drive it — but match the build type to the goal first (the box below); that's where live-session runs derail. Full sequences: references/run-your-app.md — read before running a mode.

Match the build to the goal before installing anything — this is where live-session runs derail. Two traps, same root (grabbing a build that doesn't fit the request):

1. Wrong type. Live edits (Mode C) require a dev build. A static build — a local Release (A), the default EAS sim build (B), or any build left on the sim from an earlier screenshot run — freezes its JS at build time and can never hot-reload. For a live request, ignore existing builds entirely and install a dev build (local Debug, or an EAS build with developmentClient: true). Never reconnect Metro to a static build hoping it'll reload — it won't.
2. Stale. A static look must match current source — reuse only a fingerprint-matched build, else build fresh; reuse is explicit-only.

So a leftover EAS/release build is not a shortcut for "iterate live" — it's the wrong binary. The fact that a build exists never makes it the right one.

Quick decision — default to C; A and B are explicit-only:

• C (almost everything): iterate, interact, poke the app, live edits — and most "show me my app" (current code needs a build anyway, so live+current wins). Mac → dev client builds locally; no Mac → build it on EAS (developmentClient: true). Unsure → C.
• A: only an explicit one-shot static screenshot on a Mac.
• B: only when the user names an existing/EAS build or wants a static EAS artifact (CI/sharing) — see the box above for why a static build is the wrong tool for "iterate."

Driving the device (agent-device)

agent-device is the controller. Common verbs (run each as npx --yes eas-cli@latest simulator:exec npx agent-device@latest <verb>):

For the full verb set and the argent controller alternative, see references/controllers.md.

Operating principles

The non-obvious mental model worth internalizing. Specific error→fix lookups (hung verbs, tap→press, --platform, --json, pod install locale, orphaned sessions, boot variability) live in references/troubleshooting.md.

1. Establish ground truth, then reset — don't patch-loop. Never assume an existing session or Metro is yours or healthy. Before driving, confirm:

   • cwd — you're in the intended Expo project dir (a misdirected start/exec sessions the wrong app + drops a stray .env.eas-simulator; pwd / check app.json).
   • session live — IN_PROGRESS via simulator:get --json (a stopped session keeps its id + remoteConfig, so the dotenv alone isn't proof).
   • one Metro on :8081 — reuse if it's yours, else free the port before starting (run-your-app.md).
   • build fits intent — a release build can't live-reload; if live edits are wanted and a release build is installed, install the dev build, don't reconnect.

   If current code isn't rendering after your first connect, stop poking live state: reset to baseline (stop session → clear dotenv → kill Metro) and redo the mode once; a second failure → stop and report. Never restart Metro in place, reconnect more than once, rebuild the native client to fix a JS/connection problem, or surface a preview URL while state is unknown. (A daemon drop — ERR_NGROK_3200 / Remote daemon is unavailable — is the same: reset, don't retry.)

2. exec is a wrapper, not a driver. simulator:exec loads .env.eas-simulator and spawns the command you pass; the device verbs come from the controller (npx agent-device@latest). There is no simulator:tap.

3. Act immediately; don't park an idle session. Sessions are short-lived — install and drive right after start. Leaving one idle drops the tunnel/daemon (→ reset, per #1).

4. Stop on every exit path (billing) and reset the dotenv. --non-interactive doesn't auto-stop, and a forgotten session bills until stopped. Don't start again to "retry" a slow boot — that orphans a second billed session.

5. Screenshot only the correct, fresh build. Mode C only after the dev client connects to Metro; A/B only from a build matching current source — reusing a pre-existing build is the #1 "my edits don't show" cause (see the build caveat above). (9:41 in the status bar is the sim default, not staleness.)

Stop and clean up

Stop the session (ends billing) and reset the dotenv so a later run doesn't try to reuse the dead session:

References

• references/run-your-app.md — full command sequences for modes A, B, and C (read before running a mode).
• references/controllers.md — agent-device verb reference and the argent alternative.
• references/troubleshooting.md — concrete errors and fixes.

Source of truth: Expo docs and the eas / agent-device CLIs (npx --yes eas-cli@latest simulator:* --help, agent-device --help). This skill teaches how to apply them; it doesn't replace them.