A reference guide for the Expo ecosystem, a set of tools for building React Native apps, including Expo SDK, routing, builds, submissions, and updates.

Use it when working with Expo Router, EAS services, development clients, native modules, Hermes, or React Native’s newer architecture.

It gives team roles current Expo-specific information without replacing their normal engineering responsibilities.

stack-expo — Skill for Claude Code by e-t-y-b/etyb-skills

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent

npx skills add e-t-y-b/etyb-skills --skill expo

Clone the repo

git clone --depth 1 https://github.com/e-t-y-b/etyb-skills

Made for: Claude Code.

Or install etyb, the plugin that ships this one along with the rest of its 14 skills, 5 agents, 4 hooks.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/e-t-y-b/etyb-skills/expo/github.svg)](https://agentmods.dev/skills/e-t-y-b/etyb-skills/expo)

Your own site

<a href="https://agentmods.dev/skills/e-t-y-b/etyb-skills/expo"><img src="https://agentmods.dev/badge/skills/e-t-y-b/etyb-skills/expo/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/e-t-y-b/etyb-skills/expo"><img src="https://agentmods.dev/badge/skills/e-t-y-b/etyb-skills/expo.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 240 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 3,470 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.00240	$0.03470
Opus 5.5	$0.00096	$0.01388
Sonnet 5.5	$0.00048	$0.00694
Haiku 4.5	$0.00024	$0.00347

Measured 1mo ago against content hash 20113ee4a2bc, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

stack-expo scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

stacks/expo/SKILL.md · 127 lines

How it starts

The opening of the file, as written. The whole thing — 127 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Expo Stack — Team Briefing

This is a knowledge overlay, not a new specialist. The existing ETYB team does the work — backend-architect writes the backend code, devops-engineer wires the deploys, security-engineer enforces the boundary. This pack tells each role where the current Expo knowledge lives.

Where the full briefing lives

The full Stack briefing lives in this same folder. Per-product and per-role pages are siblings of this SKILL.md. Every page carries last_verified_on stamps and authoritative-source URLs in its frontmatter; see skills/etyb/core/knowledge-currency.md for the drift-check protocol that uses them.

Stack briefing: stacks/expo/index.md
Per-product pages: stacks/expo/<product>.md — one per entry in products_covered above
Per-role views: stacks/expo/<role>.md — one per role in applies_to_roles above

When ETYB is installed locally these are read directly from disk. For third-party agents without the install, the same content is reachable as raw markdown at https://raw.githubusercontent.com/e-t-y-b/etyb-skills/main/stacks/expo/<page>.md.

When delegate_to_skills (frontmatter above) lists a first-party vendor MCP/skill that's installed in the user's environment, ETYB defers to it first. The in-repo Stack content is the curated fallback.

What changed in 2025-2026 that older training data misses

Critical context — an LLM with a 2024 cutoff will get these wrong:

The New Architecture is mandatory. SDK 51 made Fabric + TurboModules the default; SDK 53 made the old architecture opt-out impossible inside Expo; React Native 0.82 forced bridgeless mode platform-wide. As of SDK 55 / RN 0.83 you cannot opt out. Any answer that says "you can disable the new architecture" is wrong for current SDKs.
Hermes is the only JS engine. JavaScriptCore was removed from React Native; Hermes V1 is default and only. No jsEngine: 'jsc' in app.json.
expo CLI replaces react-native CLI for everything in managed and prebuild workflows. npx expo start, npx expo run:ios, npx expo prebuild, npx expo install. The old react-native run-ios is bare-only and inferior. Do not recommend it for Expo projects.
expo-cli (the global v0–v6) is dead. Use npx expo per-project. Don't npm i -g expo-cli.
EAS Update replaces CodePush. Microsoft App Center retired March 2025; for any Expo project, EAS Update with Hermes bytecode diffing + branch-based channels is the answer.
EAS Hosting is GA. Launched 2024-2025, GA in 2025. Expo Router web + API routes deploy here; the runtime is Cloudflare Workers. Plumbing differs from Vercel/Node.
Continuous Native Generation (CNG) is the recommended workflow. Do not commit ios/ and android/ folders. The native projects are regenerated by npx expo prebuild, configured by config plugins, and built by EAS Build.
Expo Router is the default router in create-expo-app since SDK 50, stable since SDK 51. Typed routes are GA. Data loaders are experimental in SDK 55. SSR/static rendering for web is GA.
Expo API Routes (+api.ts files in app/) deploy as EAS Hosting workers. They are not Node — they're Cloudflare-Workers-compatible. Many Node-only packages won't work.
Expo Push uses FCMv1 only since June 2024. Legacy FCM HTTP API is retired. APNs must use token auth (.p8 key) — certificate auth is deprecated.
The Expo Go limitations are real. Expo Go cannot load arbitrary native modules; it ships a fixed set. Any third-party library with native code that isn't already in Expo Go requires a dev client. Default new projects to a dev client unless the work is genuinely a throwaway demo.
React 19.2 in SDK 55 means: actions, useFormStatus, useOptimistic, use(), server components groundwork, the new <Activity> API. React 19 also broke a number of older RN libraries.

Read the full file on GitHub · 127 lines

Files

What ships with it

34 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

1mo ago First seen · 127 lines · 240 tokens per session scan A 20113ee4a2bc

Subscribe to this mod's changes

stack-expo is a skill published in the GitHub repository e-t-y-b/etyb-skills (11 stars, last pushed 3mo ago), licensed MIT. It adds 240 tokens to every session and 3,470 once invoked, about $0.0010 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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