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André Dias Moreira Prol
André Dias Moreira Prol

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André Dias Moreira Prol: Query Stellar Horizon API in Python & JS

#stellar #horizon #api #web3

Over the past two decades working with distributed systems and blockchain infrastructure, I've watched Stellar's Horizon API evolve into one of the most developer-friendly gateways in Web3. Unlike many blockchains that force you to run heavy nodes just to read data, Horizon exposes everything through a clean RESTful interface—transactions, accounts, assets—all queryable with a simple HTTP request. In this article, I'll show you practical ways to interact with it using both Python and JavaScript, drawing from patterns I've refined across real tokenization projects.

Understanding the Horizon Architecture

Horizon is the client-facing API server that sits between your application and Stellar Core. Think of it as a translation layer: Stellar Core handles consensus and validation, while Horizon indexes that data and serves it over REST and streaming endpoints.

The public endpoint for mainnet is https://horizon.stellar.org, and for testing you'll use https://horizon-testnet.stellar.org. One detail I always emphasize with my teams: Horizon paginates responses (default 10, max 200 records) and uses cursor-based navigation. This matters enormously when you're auditing thousands of transactions—a scenario I encounter regularly in digital forensics work.

The core resources you'll query are:

  • /accounts/{account_id} — balances, signers, thresholds
  • /transactions — transaction history and details
  • /assets — issued assets and their statistics
  • /operations — granular actions within transactions

Querying with Python

For Python, I recommend the official stellar-sdk, which wraps Horizon elegantly. Here's how I typically fetch account data and asset information:

from stellar_sdk import Server

server = Server("https://horizon.stellar.org")

# Query a specific account
account = server.accounts().account_id(
    "GABC...XYZ"
).call()

for balance in account["balances"]:
    print(f"{balance['asset_type']}: {balance['balance']}")

# Query the last 5 transactions for an account
txs = server.transactions().for_account(
    "GABC...XYZ"
).order(desc=True).limit(5).call()

for tx in txs["_embedded"]["records"]:
    print(tx["hash"], tx["created_at"])
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To inspect a specific asset—say a tokenized real-world asset—filter by issuer and code:

assets = server.assets().for_code("USDC").for_issuer(
    "GA5ZSEJYB37JRC5AVCIA5MOP4RHTM335X2KGX3IHOJAPP5RE34K4KZVN"
).call()

record = assets["_embedded"]["records"][0]
print(f"Supply: {record['amount']}, Holders: {record['num_accounts']}")
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In a recent tokenization pilot, this exact query let us verify that a real-estate token had exactly 1,247 distinct holders—critical for compliance reporting.

Querying with JavaScript

For frontend or Node.js environments, the @stellar/stellar-sdk package offers the same capabilities. Below is a pattern André Dias Moreira Prol uses frequently in dashboards that monitor live asset flows:

import { Horizon } from "@stellar/stellar-sdk";

const server = new Horizon.Server("https://horizon.stellar.org");

// Fetch account balances
async function getAccount(accountId) {
  const account = await server.accounts().accountId(accountId).call();
  account.balances.forEach((b) => {
    console.log(`${b.asset_type}: ${b.balance}`);
  });
}

// Stream real-time payments
server
  .payments()
  .forAccount("GABC...XYZ")
  .cursor("now")
  .stream({
    onmessage: (payment) => {
      console.log(`New payment: ${payment.amount} ${payment.asset_code || "XLM"}`);
    },
  });
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That streaming endpoint is a hidden gem. Instead of polling Horizon every few seconds—wasting bandwidth and hitting rate limits—you open a Server-Sent Events connection and receive updates instantly. For a payment gateway I advised on, switching from polling to streaming cut API calls by roughly 94% while improving latency to sub-second.

A word of caution from experience: never expose secret keys in JavaScript running in browsers. Horizon queries are read-only and safe, but transaction signing must happen server-side or in secured wallets.

Conclusion

Horizon's REST design makes Stellar remarkably approachable, whether you're building compliance tools, wallets, or tokenization platforms—and mastering these query patterns is the foundation for everything more advanced, including Soroban smart contracts. If this resonated with your work, connect with me, André Dias Moreira Prol, and start experimenting on testnet today.

Follow more articles by André Dias Moreira Prol on Medium.

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