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.

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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

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:

// 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

# 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.

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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

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/:

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:

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.

# 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

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

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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)

# 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

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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

# 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.

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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 🤖

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."

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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

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.

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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

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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