Add Alchemy RPC To Any Project using Cursor

You are scaffolding a flexible Alchemy JSON-RPC proxy. Apply changes directly in the repo. Do not echo full files unless I ask later.
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Step 0 — Detect environment and set "@/..." alias if Next.js
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1) If an /app directory exists → Next.js App Router mode.
2) Else if a /pages directory exists → Next.js Pages Router mode.
3) Else → Fallback Node mode.
If in a Next.js mode, open tsconfig.json and ensure:
  "baseUrl": "."
  "paths": { "@/*": ["./*"] }
Add them if missing while preserving all other options.
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Step 1 — Env templates and .gitignore (CREATE BOTH FILES)
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1) Create a file named .env.example with exactly these lines:
# Generic default upstream (used if no chain-specific env is set)
ALCHEMY_API_URL=https://eth-mainnet.g.alchemy.com/v2/<KEY>
# Optional chain-specific overrides
ALCHEMY_API_URL_ETH_MAINNET=https://eth-mainnet.g.alchemy.com/v2/<KEY>
ALCHEMY_API_URL_BASE_MAINNET=https://base-mainnet.g.alchemy.com/v2/<KEY>
ALCHEMY_API_URL_OPTIMISM_MAINNET=https://opt-mainnet.g.alchemy.com/v2/<KEY>
ALCHEMY_API_URL_ARBITRUM_MAINNET=https://arb-mainnet.g.alchemy.com/v2/<KEY>
ALCHEMY_API_URL_POLYGON_MAINNET=https://polygon-mainnet.g.alchemy.com/v2/<KEY>
2) In the TERMINAL, create .env.local if it does not already exist by copying from .env.example (do not overwrite existing):
node -e "const fs=require('fs');if(!fs.existsSync('.env.local')){fs.copyFileSync('.env.example','.env.local');console.log('Created .env.local from .env.example');}else{console.log('.env.local already exists, not modified');}"
3) Open .gitignore. If it does not already include a line for .env.local, append:
.env.local
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Step 2 — RPC proxy (create ONE implementation based on the detected mode)
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--- A) Next.js App Router (app/api/rpc/route.ts, Edge) ---
If /app exists, create app/api/rpc/route.ts with this content:
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import { NextRequest, NextResponse } from "next/server";
export const runtime = "edge";
// Optional per-chain envs, fallback to generic ALCHEMY_API_URL
const URLS: Record<string, string | undefined> = {
  "eth-mainnet": process.env.ALCHEMY_API_URL_ETH_MAINNET,
  "base-mainnet": process.env.ALCHEMY_API_URL_BASE_MAINNET,
  "optimism-mainnet": process.env.ALCHEMY_API_URL_OPTIMISM_MAINNET,
  "arbitrum-mainnet": process.env.ALCHEMY_API_URL_ARBITRUM_MAINNET,
  "polygon-mainnet": process.env.ALCHEMY_API_URL_POLYGON_MAINNET,
};
export async function POST(request: NextRequest) {
  const chain = request.headers.get("x-chain") || "eth-mainnet";
  const upstream = URLS[chain] || process.env.ALCHEMY_API_URL;
  if (!upstream) {
    return NextResponse.json(
      { error: \`Missing upstream for chain "\${chain}". Set ALCHEMY_API_URL or chain-specific env.\` },
      { status: 500 }
    );
  }
  let payload: unknown;
  try {
    payload = await request.json();
  } catch {
    return NextResponse.json({ error: "Invalid JSON body" }, { status: 400 });
  }
  const res = await fetch(upstream, {
    method: "POST",
    headers: { "content-type": "application/json" }, // do not forward cookies or browser headers
    body: JSON.stringify(payload),
    cache: "no-store",
  });
  let json: any;
  try {
    json = await res.json();
  } catch {
    return NextResponse.json(
      { error: "Upstream returned non-JSON", status: res.status },
      { status: 502 }
    );
  }
  return NextResponse.json(json, {
    status: res.ok ? 200 : res.status || 502,
    headers: { "cache-control": "no-store" },
  });
}
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--- B) Next.js Pages Router (pages/api/rpc.ts) ---
Else if /pages exists, create pages/api/rpc.ts with this content:
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import type { NextApiRequest, NextApiResponse } from "next";
const URLS: Record<string, string | undefined> = {
  "eth-mainnet": process.env.ALCHEMY_API_URL_ETH_MAINNET,
  "base-mainnet": process.env.ALCHEMY_API_URL_BASE_MAINNET,
  "optimism-mainnet": process.env.ALCHEMY_API_URL_OPTIMISM_MAINNET,
  "arbitrum-mainnet": process.env.ALCHEMY_API_URL_ARBITRUM_MAINNET,
  "polygon-mainnet": process.env.ALCHEMY_API_URL_POLYGON_MAINNET,
};
export default async function handler(req: NextApiRequest, res: NextApiResponse) {
  if (req.method !== "POST") {
    res.setHeader("Allow", "POST");
    return res.status(405).json({ error: "Method not allowed" });
  }
  const chain = (req.headers["x-chain"] as string) || "eth-mainnet";
  const upstream = URLS[chain] || process.env.ALCHEMY_API_URL;
  if (!upstream) {
    return res
      .status(500)
      .json({ error: \`Missing upstream for chain "\${chain}". Set ALCHEMY_API_URL or chain-specific env.\` });
  }
  const payload = req.body ?? {};
  const upstreamRes = await fetch(upstream, {
    method: "POST",
    headers: { "content-type": "application/json" },
    body: typeof payload === "string" ? payload : JSON.stringify(payload),
    cache: "no-store",
  });
  let data: any = null;
  try {
    data = await upstreamRes.json();
  } catch {
    return res.status(502).json({ error: "Upstream returned non-JSON", status: upstreamRes.status });
  }
  res.setHeader("cache-control", "no-store");
  return res.status(upstreamRes.ok ? 200 : upstreamRes.status || 502).json(data);
}
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--- C) Fallback Node mode (server/rpc-proxy.mjs + npm script) ---
Else (no /app and no /pages), create server/rpc-proxy.mjs with this content:
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import http from "node:http";
import { readFileSync, existsSync } from "node:fs";
import { resolve } from "node:path";
// Minimal dotenv loader for .env.local or .env
function loadDotEnv() {
  const files = [".env.local", ".env"];
  for (const f of files) {
    const p = resolve(process.cwd(), f);
    if (existsSync(p)) {
      const text = readFileSync(p, "utf8");
      for (const line of text.split(/\\r?\\n/)) {
        const m = line.match(/^\\s*([A-Z0-9_]+)\\s*=\\s*(.*)\\s*$/);
        if (!m) continue;
        const [, k, raw] = m;
        if (process.env[k]) continue;
        const v = raw.replace(/^"(.*)"$/, "$1").replace(/^'(.*)'$/, "$1");
        process.env[k] = v;
      }
    }
  }
}
loadDotEnv();
// Chain map with optional overrides, fallback to generic ALCHEMY_API_URL
const URLS = {
  "eth-mainnet": process.env.ALCHEMY_API_URL_ETH_MAINNET,
  "base-mainnet": process.env.ALCHEMY_API_URL_BASE_MAINNET,
  "optimism-mainnet": process.env.ALCHEMY_API_URL_OPTIMISM_MAINNET,
  "arbitrum-mainnet": process.env.ALCHEMY_API_URL_ARBITRUM_MAINNET,
  "polygon-mainnet": process.env.ALCHEMY_API_URL_POLYGON_MAINNET,
};
const PORT = process.env.PORT ? Number(process.env.PORT) : 8787;
const server = http.createServer(async (req, res) => {
  // CORS for local dev
  res.setHeader("Access-Control-Allow-Origin", "*");
  res.setHeader("Access-Control-Allow-Methods", "POST, OPTIONS");
  res.setHeader("Access-Control-Allow-Headers", "Content-Type, x-chain");
  if (req.method === "OPTIONS") {
    res.statusCode = 204;
    res.end();
    return;
  }
  if (req.url !== "/rpc" || req.method !== "POST") {
    res.statusCode = 404;
    res.setHeader("content-type", "application/json");
    res.end(JSON.stringify({ error: "Not found" }));
    return;
  }
  const chain = req.headers["x-chain"]?.toString() || "eth-mainnet";
  const upstream = URLS[chain] || process.env.ALCHEMY_API_URL;
  if (!upstream) {
    res.statusCode = 500;
    res.setHeader("content-type", "application/json");
    res.end(JSON.stringify({ error: \`Missing upstream for chain "\${chain}". Set ALCHEMY_API_URL or chain-specific env.\` }));
    return;
  }
  let body = "";
  for await (const chunk of req) body += chunk;
  const payload = body || "{}";
  try {
    const upstreamRes = await fetch(upstream, {
      method: "POST",
      headers: { "content-type": "application/json" },
      body: payload,
      cache: "no-store",
    });
    const text = await upstreamRes.text();
    res.statusCode = upstreamRes.ok ? 200 : upstreamRes.status || 502;
    res.setHeader("content-type", "application/json");
    res.setHeader("cache-control", "no-store");
    res.end(text);
  } catch (e) {
    res.statusCode = 502;
    res.setHeader("content-type", "application/json");
    res.end(JSON.stringify({ error: "Upstream fetch failed", detail: String(e) }));
  }
});
server.listen(PORT, () => {
  console.log(\`[rpc-proxy] listening on http://localhost:\${PORT}/rpc\`);
});
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Also, if in Fallback Node mode, update package.json to include this script (add or merge without removing existing scripts):
"rpc-proxy": "node server/rpc-proxy.mjs"
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Step 3 — Optional tiny helper and self-test (Next.js modes only)
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If in a Next.js mode, create lib/rpc.ts with this content:
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type JsonRpcError = { code: number; message: string; data?: unknown };
type JsonRpcResponse<T = unknown> = { jsonrpc: "2.0"; id: number | string; result?: T; error?: JsonRpcError };
export async function rpc<T = unknown>(
  method: string,
  params: unknown[] = [],
  chain: "eth-mainnet" | "base-mainnet" | "optimism-mainnet" | "arbitrum-mainnet" | "polygon-mainnet" = "eth-mainnet"
): Promise<T> {
  const res = await fetch("/api/rpc", {
    method: "POST",
    headers: { "content-type": "application/json", "x-chain": chain },
    body: JSON.stringify({ jsonrpc: "2.0", id: Date.now(), method, params }),
    cache: "no-store",
  });
  if (!res.ok) {
    const text = await res.text().catch(() => "");
    throw new Error(\`RPC HTTP \${res.status}\${text ? \`: \${text}\` : ""}\`);
  }
  const data = (await res.json()) as JsonRpcResponse<T>;
  if (data.error) throw new Error(data.error.message || "RPC error");
  return data.result as T;
}
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If in App Router mode, create a dev-only page at app/rpc-selftest/page.tsx with this content:
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"use client";
import { useEffect, useState } from "react";
import { rpc } from "@/lib/rpc";
function hexToInt(h: string) { try { return parseInt(h, 16); } catch { return NaN; } }
export default function SelfTest() {
  const [ethBlock, setEthBlock] = useState<number | null>(null);
  const [baseBlock, setBaseBlock] = useState<number | null>(null);
  const [err, setErr] = useState<string | null>(null);
  useEffect(() => {
    (async () => {
      try {
        const ethHex = await rpc<string>("eth_blockNumber", [], "eth-mainnet");
        const baseHex = await rpc<string>("eth_blockNumber", [], "base-mainnet");
        setEthBlock(hexToInt(ethHex));
        setBaseBlock(hexToInt(baseHex));
      } catch (e: any) {
        setErr(e?.message ?? "Unknown error");
      }
    })();
  }, []);
  return (
    <div className="min-h-screen p-6">
      <h1 className="text-2xl font-semibold">RPC proxy self test</h1>
      <p className="text-sm text-gray-600 mt-1">Calls /api/rpc with x-chain header.</p>
      {err ? (
        <p className="mt-4 text-red-600">Error: {err}</p>
      ) : (
        <div className="mt-4 space-y-2">
          <div>eth-mainnet block: <b>{ethBlock ?? "…"}</b></div>
          <div>base-mainnet block: <b>{baseBlock ?? "…"}</b></div>
        </div>
      )}
    </div>
  );
}
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If in Pages Router mode, create docs/RPC-TEST.md with these contents (no code fences needed):
# RPC proxy test
With the dev server running:
curl -s -X POST http://localhost:3000/api/rpc \
  -H 'content-type: application/json' \
  -H 'x-chain: eth-mainnet' \
  -d '{"jsonrpc":"2.0","id":1,"method":"eth_chainId","params":[]}'
curl -s -X POST http://localhost:3000/api/rpc \
  -H 'content-type: application/json' \
  -H 'x-chain: base-mainnet' \
  -d '{"jsonrpc":"2.0","id":1,"method":"eth_chainId","params":[]}'
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Step 4 — Final instructions for the developer (print in chat)
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Tell me:
- Which mode was detected (App Router, Pages Router, or Fallback Node).
- Which files you created or updated.
- Next steps:
  - Open .env.local and replace <KEY> with your real Alchemy keys (or set per-chain URLs).
  - If Next.js: run npm run dev.
      - App Router: visit http://localhost:3000/rpc-selftest
      - Pages Router: use the curl examples in docs/RPC-TEST.md
  - If Fallback Node: run npm run rpc-proxy and POST JSON-RPC to http://localhost:8787/rpc with optional header x-chain.