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Build a Crypto Portfolio Tracker in Under 50 Lines of Code

#webdev #tutorial #cryptocurrency #javascript

You want to track your crypto portfolio but don't want to build an entire backend or deal with CoinGecko rate limits. Here's how to build a working portfolio tracker in under 50 lines of JavaScript.

No API key needed. No signup. Just code.

What We're Building

A command-line portfolio tracker that:

  • Fetches live prices for any coins you hold
  • Calculates your total portfolio value in USD
  • Shows profit/loss per coin
  • Runs with a single node portfolio.js command

The API

We'll use the Frostbyte API — it returns real-time prices for 500+ coins with no authentication required.

Quick test:

curl -s https://agent-gateway-kappa.vercel.app/prices | python3 -m json.tool | head -20
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Response:

{
  "count": 527,
  "prices": {
    "BTC": "71312.5",
    "ETH": "2080.95",
    "SOL": "88.80",
    "DOGE": "0.094",
    "XMR": "363.8"
  }
}
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527 coins, updated in real time, zero authentication.

Step 1: Define Your Holdings

Create portfolio.js:

const HOLDINGS = [
  { coin: 'BTC', amount: 0.5,  buyPrice: 42000 },
  { coin: 'ETH', amount: 10,   buyPrice: 2200 },
  { coin: 'SOL', amount: 100,  buyPrice: 25 },
];
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Replace with your actual holdings and buy prices.

Step 2: Fetch Live Prices 

async function getPrices() {
  const res = await fetch('https://agent-gateway-kappa.vercel.app/prices');
  const data = await res.json();
  return data.prices;
}
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That's it. No headers, no API keys, no OAuth dance.

Step 3: Calculate Portfolio Value 

async function showPortfolio() {
  const prices = await getPrices();
  let totalValue = 0, totalCost = 0;

  console.log('\n  COIN   | QTY      | PRICE       | VALUE       | P/L');
  console.log('  -------|----------|-------------|-------------|--------');

  for (const h of HOLDINGS) {
    const price = parseFloat(prices[h.coin]);
    if (!price) { console.log(`  ${h.coin}: not found`); continue; }

    const value = h.amount * price;
    const cost = h.amount * h.buyPrice;
    const pl = ((price - h.buyPrice) / h.buyPrice * 100).toFixed(1);
    const sign = price >= h.buyPrice ? '+' : '';

    totalValue += value;
    totalCost += cost;

    console.log(
      `  ${h.coin.padEnd(6)} | ${String(h.amount).padEnd(8)} | $${price.toLocaleString().padStart(10)} | $${value.toLocaleString().padStart(10)} | ${sign}${pl}%`
    );
  }

  const totalPL = ((totalValue - totalCost) / totalCost * 100).toFixed(1);
  console.log('  -------|----------|-------------|-------------|--------');
  console.log(`  TOTAL  |          |             | $${totalValue.toLocaleString().padStart(10)} | ${totalValue >= totalCost ? '+' : ''}${totalPL}%\n`);
}

showPortfolio();
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Full Code (44 Lines)

Here's the complete portfolio.js:

const HOLDINGS = [
  { coin: 'BTC', amount: 0.5,  buyPrice: 42000 },
  { coin: 'ETH', amount: 10,   buyPrice: 2200 },
  { coin: 'SOL', amount: 100,  buyPrice: 25 },
];

async function getPrices() {
  const res = await fetch('https://agent-gateway-kappa.vercel.app/prices');
  const data = await res.json();
  return data.prices;
}

async function showPortfolio() {
  const prices = await getPrices();
  let totalValue = 0, totalCost = 0;

  console.log('\n  COIN   | QTY      | PRICE       | VALUE       | P/L');
  console.log('  -------|----------|-------------|-------------|--------');

  for (const h of HOLDINGS) {
    const price = parseFloat(prices[h.coin]);
    if (!price) { console.log(`  ${h.coin}: not found`); continue; }

    const value = h.amount * price;
    const cost = h.amount * h.buyPrice;
    const pl = ((price - h.buyPrice) / h.buyPrice * 100).toFixed(1);
    const sign = price >= h.buyPrice ? '+' : '';

    totalValue += value;
    totalCost += cost;

    console.log(
      `  ${h.coin.padEnd(6)} | ${String(h.amount).padEnd(8)} | $${price.toLocaleString().padStart(10)} | $${value.toLocaleString().padStart(10)} | ${sign}${pl}%`
    );
  }

  const totalPL = ((totalValue - totalCost) / totalCost * 100).toFixed(1);
  console.log('  -------|----------|-------------|-------------|--------');
  console.log(`  TOTAL  |          |             | $${totalValue.toLocaleString().padStart(10)} | ${totalValue >= totalCost ? '+' : ''}${totalPL}%\n`);
}

showPortfolio();
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Run it:

node portfolio.js
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Add Auto-Refresh

Want a live dashboard? Add one line:

setInterval(showPortfolio, 30000); // refresh every 30s
showPortfolio();
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Other Free Endpoints

The same API has more tools you can use without an API key:

Your public IP:

curl https://agent-gateway-kappa.vercel.app/ip
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IP geolocation (city, country, ISP):

curl https://agent-gateway-kappa.vercel.app/ip/json
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Get an API key for 40+ additional endpoints (200 free credits):

curl -X POST https://agent-gateway-kappa.vercel.app/api/keys/create
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This unlocks DNS lookups, website screenshots, code execution, web scraping, and more. Full docs at the API catalog.

Built with Frostbyte API — free crypto, geo, and developer APIs.

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