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.
npx skills add fanfan-de/anybox --skill expo-brownfieldgit clone --depth 1 https://github.com/fanfan-de/anyboxWrote 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.
[](https://agentmods.dev/skills/fanfan-de/anybox/expo-brownfield)<a href="https://agentmods.dev/skills/fanfan-de/anybox/expo-brownfield"><img src="https://agentmods.dev/badge/skills/fanfan-de/anybox/expo-brownfield/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.
<a href="https://agentmods.dev/skills/fanfan-de/anybox/expo-brownfield"><img src="https://agentmods.dev/badge/skills/fanfan-de/anybox/expo-brownfield.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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 | $0.00064 | $0.00723 |
| Opus 5 | $0.00032 | $0.00362 |
| Sonnet 5 | $0.00013 | $0.00145 |
| Haiku 4.5 | $0.00006 | $0.00072 |
Grade B, and why
expo-brownfield scanned grade B with 1 finding 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 9d 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.
Asks for rootmediumPrivilege escalation
A mod that escalates privileges can change anything on the machine, not only the project.
The integrated approach additionally requires **CocoaPods** on iOS (`sudo gem install cocoapods`). The isolated approach does **not** require CocoaPods or any RN tooling in the consuming native app. This is a copy
91% identical to expo-brownfield — 37 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 55 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Expo Brownfield
A brownfield app is an existing native iOS or Android app that adopts React Native incrementally, as opposed to a greenfield app that is React Native from day one.
Expo supports two distinct ways to add React Native to a brownfield project:
| Approach | What ships to the native app | When to choose |
|---|---|---|
| Isolated | Prebuilt AAR / XCFramework | Native team doesn't need Node or RN tooling; RN code can live in a separate repo |
| Integrated | React Native sources added to the existing Gradle / CocoaPods build | One team owns everything; comfortable with RN tooling; wants a single build |
For the full decision matrix, see ./references/comparison.md.
Pick an approach
Use these quick rules — fall through to comparison.md for anything ambiguous.
- Choose isolated if the iOS/Android team must consume RN as a regular library dependency (AAR or XCFramework), without installing Node, Yarn, or the React Native build toolchain.
- Choose isolated if RN code and native code live in separate repositories or release on independent cadences.
- Choose integrated if a single team owns both the native and RN code and is willing to add React Native + Expo to the native project's Gradle and CocoaPods setup.
- Choose integrated if you want hot reload and JS source maps to work seamlessly inside the existing native build process.
References
- ./references/brownfield-isolated.md -- Build RN as AAR/XCFramework and consume from the native app (BrownfieldActivity, ReactNativeViewController, ReactNativeView)
- ./references/brownfield-integrated.md -- Add RN and Expo directly to existing Gradle and CocoaPods builds (ReactActivity, RCTRootView, Podfile)
- ./references/comparison.md -- Decision criteria, trade-offs, and scenario mapping for choosing an approach
- ./references/troubleshooting.md -- Metro connection, build, signing, and module-resolution issues common to both approaches
What ships with it
5 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.
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.
- 9d ago First seen · 55 lines · 64 tokens per session scan B 6c17e12e1ec3
expo-brownfield is a skill published in the GitHub repository fanfan-de/anybox (57 stars, last pushed 1mo ago), licensed MIT. It adds 64 tokens to every session and 723 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it B with 1 finding (asks for root). It is 91% identical to expo-brownfield, differing in 37 lines, and is treated as a copy.
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