---
name: frontend-playbook
description: The complete build-to-production pipeline for Ethereum dApps. Fork mode setup, IPFS deployment, Vercel config, ENS subdomain setup, and the full production checklist. Built around Scaffold-ETH 2 but applicable to any Ethereum frontend project. Use when deploying any dApp to production.
---

# Frontend Playbook

## What You Probably Got Wrong

**"I'll use `yarn chain`."** Wrong. `yarn chain` gives you an empty local chain with no protocols, no tokens, no state. `yarn fork --network base` gives you a copy of real Base with Uniswap, Aave, USDC, real whale balances — everything. Always fork.

**"I deployed to IPFS and it works."** Did the CID change? If not, you deployed stale output. Did routes work? Without `trailingSlash: true`, every route except `/` returns 404. Did you check the OG image? Without `NEXT_PUBLIC_PRODUCTION_URL`, it points to `localhost:3000`.

**"I'll set up the project manually."** Don't. `npx create-eth@latest` handles everything — Foundry, Next.js, RainbowKit, scaffold hooks. Never run `forge init` or create Next.js projects from scratch.

---

## Fork Mode Setup

### Why Fork, Not Chain

```
yarn chain (WRONG)              yarn fork --network base (CORRECT)
└─ Empty local chain            └─ Fork of real Base mainnet
└─ No protocols                 └─ Uniswap, Aave, etc. available
└─ No tokens                    └─ Real USDC, WETH exist
└─ Testing in isolation         └─ Test against REAL state
```

### Setup

```bash
npx create-eth@latest          # Select: foundry, target chain, name
cd <project-name>
yarn install
yarn fork --network base       # Terminal 1: fork of real Base
yarn deploy                    # Terminal 2: deploy contracts to fork
yarn start                     # Terminal 3: Next.js frontend
```

### Critical: Chain ID Gotcha

**When using fork mode, the frontend target network MUST be `chains.foundry` (chain ID 31337), NOT the chain you're forking.**

The fork runs locally on Anvil with chain ID 31337. Even if you're forking Base:

```typescript
// scaffold.config.ts during development
targetNetworks: [chains.foundry],  // ✅ NOT chains.base!
```

Only switch to `chains.base` when deploying contracts to the REAL network.

### Enable Block Mining

```bash
# In a new terminal — REQUIRED for time-dependent logic
cast rpc anvil_setIntervalMining 1
```

Without this, `block.timestamp` stays FROZEN. Any contract logic using timestamps (deadlines, expiry, vesting) will break silently.

**Make it permanent** by editing `packages/foundry/package.json` to add `--block-time 1` to the fork script.

---

## Deploying to IPFS (Recommended)

IPFS is the recommended deploy path for SE2. Avoids Vercel's memory limits entirely. Produces a fully decentralized static site.

### Full Build Command

```bash
cd packages/nextjs
rm -rf .next out  # ALWAYS clean first

NEXT_PUBLIC_PRODUCTION_URL="https://yourapp.yourname.eth.link" \
  NODE_OPTIONS="--require ./polyfill-localstorage.cjs" \
  NEXT_PUBLIC_IPFS_BUILD=true \
  NEXT_PUBLIC_IGNORE_BUILD_ERROR=true \
  yarn build

# Upload to BuidlGuidl IPFS
yarn bgipfs upload out
# Save the CID!
```

### Node 25+ localStorage Polyfill (REQUIRED)

Node.js 25+ ships a built-in `localStorage` object that's MISSING standard WebStorage API methods (`getItem`, `setItem`). This breaks `next-themes`, RainbowKit, and any library that calls `localStorage.getItem()` during static page generation.

**Error you'll see:**
```
TypeError: localStorage.getItem is not a function
Error occurred prerendering page "/_not-found"
```

**The fix:** Create `polyfill-localstorage.cjs` in `packages/nextjs/`:
```javascript
if (typeof globalThis.localStorage !== "undefined" &&
    typeof globalThis.localStorage.getItem !== "function") {
  const store = new Map();
  globalThis.localStorage = {
    getItem: (key) => store.get(key) ?? null,
    setItem: (key, value) => store.set(key, String(value)),
    removeItem: (key) => store.delete(key),
    clear: () => store.clear(),
    key: (index) => [...store.keys()][index] ?? null,
    get length() { return store.size; },
  };
}
```

**Why `--require` and not `instrumentation.ts`?** Next.js spawns a separate build worker process for prerendering. `--require` injects into EVERY Node process (including workers). `next.config.ts` polyfill only runs in the main process. `instrumentation.ts` doesn't run in the build worker. Only `--require` works.

### IPFS Routing — Why Routes Break

IPFS gateways serve static files. No server handles routing. Three things MUST be true:

**1. `output: "export"` in next.config.ts** — generates static HTML files.

**2. `trailingSlash: true` (CRITICAL)** — This is the #1 reason routes break:
- `trailingSlash: false` (default) → generates `debug.html`
- `trailingSlash: true` → generates `debug/index.html`
- IPFS gateways resolve directories to `index.html` automatically, but NOT bare filenames
- Without trailing slash: `/debug` → 404 ❌
- With trailing slash: `/debug` → `debug/` → `debug/index.html` ✅

**3. Pages must survive static prerendering** — any page that crashes during `yarn build` (browser APIs at import time, localStorage) gets skipped silently → 404 on IPFS.

**The complete IPFS-safe next.config.ts pattern:**
```typescript
const isIpfs = process.env.NEXT_PUBLIC_IPFS_BUILD === "true";
if (isIpfs) {
  nextConfig.output = "export";
  nextConfig.trailingSlash = true;
  nextConfig.images = { unoptimized: true };
}
```

**SE2's block explorer pages** use `localStorage` at import time and crash during static export. Rename `app/blockexplorer` to `app/_blockexplorer-disabled` if not needed.

### Stale Build Detection

**The #1 IPFS footgun:** You edit code, then deploy the OLD build.

```bash
# MANDATORY after ANY code change:
rm -rf .next out                     # 1. Delete old artifacts
# ... run full build command ...     # 2. Rebuild from scratch
grep -l "YOUR_STRING" out/_next/static/chunks/app/*.js  # 3. Verify changes present

# Timestamp check:
stat -f '%Sm' app/page.tsx           # Source modified time
stat -f '%Sm' out/                   # Build output time
# Source NEWER than out/ = STALE BUILD. Rebuild first!
```

**The CID is proof:** If the IPFS CID didn't change after a deploy, you deployed the same content. A real code change ALWAYS produces a new CID.

### Verify Routes After Deploy

```bash
ls out/*/index.html                  # Each route has a directory + index.html
curl -s -o /dev/null -w "%{http_code}" -L "https://GATEWAY/ipfs/CID/debug/"
# Should return 200, not 404
```

---

## Deploying to Vercel (Alternative)

SE2 is a monorepo — Vercel needs special configuration.

### Configuration

1. **Root Directory:** `packages/nextjs`
2. **Install Command:** `cd ../.. && yarn install`
3. **Build Command:** leave default (`next build`)
4. **Output Directory:** leave default (`.next`)

```bash
# Via API:
curl -X PATCH "https://api.vercel.com/v9/projects/PROJECT_ID" \
  -H "Authorization: Bearer $VERCEL_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"rootDirectory": "packages/nextjs", "installCommand": "cd ../.. && yarn install"}'
```

### Common Failures

| Error | Cause | Fix |
|-------|-------|-----|
| "No Next.js version detected" | Root Directory not set | Set to `packages/nextjs` |
| "cd packages/nextjs: No such file" | Build command has `cd` | Clear it — root dir handles this |
| OOM / exit code 129 | SE2 monorepo exceeds 8GB | Use IPFS instead, or `vercel --prebuilt` |

### Decision Tree

```
Want to deploy SE2?
├─ IPFS (recommended) → yarn ipfs / manual build + upload
│   └─ Fully decentralized, no memory limits, works with ENS
├─ Vercel → Set rootDirectory + installCommand
│   └─ Fast CDN, but centralized. May OOM on large projects
└─ vercel --prebuilt → Build locally, push artifacts to Vercel
    └─ Best of both: local build power + Vercel CDN
```

---

## ENS Subdomain Setup

Two mainnet transactions to point an ENS subdomain at your IPFS deployment.

### Transaction 1: Create Subdomain (new apps only)

1. Open `https://app.ens.domains/yourname.eth`
2. Go to "Subnames" tab → "New subname"
3. Enter the label (e.g. `myapp`) → Next → Skip profile → Open Wallet → Confirm
4. If gas is stuck: switch MetaMask to Ethereum → Activity tab → "Speed up"

### Transaction 2: Set IPFS Content Hash

1. Navigate to `https://app.ens.domains/myapp.yourname.eth`
2. "Records" tab → "Edit Records" → "Other" tab
3. Paste in Content Hash field: `ipfs://<CID>`
4. Save → Open Wallet → Confirm in MetaMask

For **updates** to an existing app: skip Tx 1, only do Tx 2.

### Verify

```bash
# 1. Onchain content hash matches
RESOLVER=$(cast call 0x00000000000C2e074eC69A0dFb2997BA6C7d2e1e \
  "resolver(bytes32)(address)" $(cast namehash myapp.yourname.eth) \
  --rpc-url https://eth.llamarpc.com)
cast call $RESOLVER "contenthash(bytes32)(bytes)" \
  $(cast namehash myapp.yourname.eth) --rpc-url https://eth.llamarpc.com

# 2. Gateway responds (may take 5-15 min for cache)
curl -s -o /dev/null -w "%{http_code}" -L "https://myapp.yourname.eth.link"

# 3. OG metadata correct (not localhost)
curl -s -L "https://myapp.yourname.eth.link" | grep 'og:image'
```

**Use `.eth.link` NOT `.eth.limo`** — `.eth.link` works better on mobile.

---

## Go to Production — Complete Checklist

When the user says "ship it", follow this EXACT sequence.

### Step 1: Final Code Review 🤖
- All feedback incorporated
- No duplicate h1, no raw addresses, no shared isLoading
- `scaffold.config.ts` has `rpcOverrides` and `pollingInterval: 3000`

### Step 2: Choose Domain 👤
Ask: *"What subdomain do you want? e.g. `myapp.yourname.eth` → `myapp.yourname.eth.link`"*

### Step 3: Generate OG Image + Fix Metadata 🤖
- Create 1200×630 PNG (`public/thumbnail.png`) — NOT the stock SE2 thumbnail
- Set `NEXT_PUBLIC_PRODUCTION_URL` to the live domain
- Verify `og:image` will resolve to an absolute production URL

### Step 4: Clean Build + IPFS Deploy 🤖
```bash
cd packages/nextjs && rm -rf .next out
NEXT_PUBLIC_PRODUCTION_URL="https://myapp.yourname.eth.link" \
  NODE_OPTIONS="--require ./polyfill-localstorage.cjs" \
  NEXT_PUBLIC_IPFS_BUILD=true NEXT_PUBLIC_IGNORE_BUILD_ERROR=true \
  yarn build

# Verify before uploading:
ls out/*/index.html                        # Routes exist
grep 'og:image' out/index.html             # Not localhost
stat -f '%Sm' app/page.tsx                 # Source older than out/
stat -f '%Sm' out/

yarn bgipfs upload out                     # Save the CID
```

### Step 5: Share for Approval 👤
Send: *"Build ready for review: `https://community.bgipfs.com/ipfs/<CID>`"*
**Wait for approval before touching ENS.**

### Step 6: Set ENS 🤖
Create subdomain (if new) + set IPFS content hash. Two mainnet transactions.

### Step 7: Verify 🤖
- Content hash matches onchain
- `.eth.link` gateway responds with 200
- OG image loads correctly
- Routes work (`/debug/`, etc.)

### Step 8: Report 👤
*"Live at `https://myapp.yourname.eth.link` — ENS content hash confirmed onchain, unfurl metadata set."*

---

## Build Verification Process

A build is NOT done when the code compiles. It's done when you've tested it like a real user.

### Phase 1: Code QA (Automated)
- Scan `.tsx` files for raw address strings (should use `<Address/>`)
- Scan for shared `isLoading` state across multiple buttons
- Scan for missing `disabled` props on transaction buttons
- Verify RPC config and polling interval
- Verify OG metadata with absolute URLs
- Verify no public RPCs in any file

### Phase 2: Smart Contract Testing
```bash
forge test                    # All tests pass
forge test --fuzz-runs 10000  # Fuzz testing
```
Test edge cases: zero amounts, max amounts, unauthorized callers, reentrancy attempts.

### Phase 3: Browser Testing (THE REAL TEST)

Open the app and do a FULL walkthrough:

1. **Load the app** — does it render correctly?
2. **Check page title** — is it correct, not "Scaffold-ETH 2"?
3. **Connect wallet** — does the connect flow work?
4. **Wrong network** — connect on wrong chain, verify "Switch to Base" appears
5. **Switch network** — click the switch button, verify it works
6. **Approve flow** — verify approve button shows, click it, wait for tx, verify action button appears
7. **Main action** — click primary action, verify loader, wait for tx, verify state updates
8. **Error handling** — reject a transaction in wallet, verify UI recovers
9. **Address displays** — all addresses showing ENS/blockies, not raw hex?
10. **Share URL** — check OG unfurl (image, title, description)

### Phase 4: QA Sub-Agent (Complex Builds)
For bigger projects, spawn a sub-agent with fresh context. Give it the repo path and deployed URL. It reads all code against the UX rules, opens a browser, clicks through independently, and reports issues.

---

## Don't Do These

- ❌ `yarn chain` — use `yarn fork --network <chain>`
- ❌ `forge init` — use `npx create-eth@latest`
- ❌ Manual Next.js setup — SE2 handles it
- ❌ Manual wallet connection — SE2 has RainbowKit pre-configured
- ❌ Edit `deployedContracts.ts` — it's auto-generated by `yarn deploy`
- ❌ Hardcode API keys in `scaffold.config.ts` — use `.env.local`
- ❌ Use `mainnet.base.org` in production — use Alchemy or similar

---

## Resources

- **SE2 Docs:** https://docs.scaffoldeth.io/
- **UI Components:** https://ui.scaffoldeth.io/
- **SpeedRun Ethereum:** https://speedrunethereum.com/
- **ETH Tech Tree:** https://www.ethtechtree.com
- **BuidlGuidl IPFS:** https://upload.bgipfs.com