Harmony API Quick Start Guide

bex.co provides high-performance, reliable Harmony infrastructure through our comprehensive JSON-RPC API. Connect to Ethereum mainnet, testnets, and layer 2 solutions with enterprise-grade reliability and developer-friendly tools.

Overview

Our Harmony API supports:

Harmony Mainnet and all major testnets (Sepolia, Holesky)
Layer 2 Solutions (Polygon, Arbitrum, Optimism)
Full JSON-RPC Specification with debug and trace methods
WebSocket Connections for real-time data
Archive Node Access for historical data
MEV Protection and transaction simulation

Quick Start

Step 1: Get Your API Key

Visit bex.co Dashboard
Sign up for a free account if you haven't already
Create a new API key for Harmony
Select your target network (Mainnet, Sepolia, etc.)

Step 2: Make Your First Request

Using cURL

bash

curl -X POST https://api.bex.co/harmony/${accessKey} \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_blockNumber",
    "params": [],
    "id": 1
  }'

Using JavaScript (Fetch)

javascript

const response = await fetch('https://api.bex.co/harmony/${accessKey}', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    jsonrpc: '2.0',
    method: 'eth_blockNumber',
    params: [],
    id: 1
  })
});
 
const data = await response.json();
console.log('Current block number:', parseInt(data.result, 16));

Using Python

python

import requests
import json
 
url = "https://api.bex.co/harmony/${accessKey}"
payload = {
    "jsonrpc": "2.0",
    "method": "eth_blockNumber",
    "params": [],
    "id": 1
}
 
response = requests.post(url, json=payload)
result = response.json()
print(f"Current block number: {int(result['result'], 16)}")

Core RPC Methods

Account Information

javascript

// Get account balance
{
  "jsonrpc": "2.0",
  "method": "eth_getBalance",
  "params": ["0x742D5Cc6bF2442E8C7c74c7b4Be6AB9d6f10f5B4", "latest"],
  "id": 1
}
 
// Get transaction count (nonce)
{
  "jsonrpc": "2.0",
  "method": "eth_getTransactionCount",
  "params": ["0x742D5Cc6bF2442E8C7c74c7b4Be6AB9d6f10f5B4", "latest"],
  "id": 1
}

Block Information

javascript

// Get latest block
{
  "jsonrpc": "2.0",
  "method": "eth_getBlockByNumber",
  "params": ["latest", true],
  "id": 1
}
 
// Get block by hash
{
  "jsonrpc": "2.0",
  "method": "eth_getBlockByHash",
  "params": ["0x1234...abcd", true],
  "id": 1
}

Transaction Operations

javascript

// Get transaction by hash
{
  "jsonrpc": "2.0",
  "method": "eth_getTransactionByHash",
  "params": ["0x1234...abcd"],
  "id": 1
}
 
// Send raw transaction
{
  "jsonrpc": "2.0",
  "method": "eth_sendRawTransaction",
  "params": ["0x1234...abcd"],
  "id": 1
}

Network Endpoints

Mainnet

HTTP: https://api.bex.co/harmony/${accessKey}
WebSocket: wss://api.bex.co/harmony/${accessKey}

Testnets

Sepolia: https://ethereum-sepolia.bex.co/<your-api-key>
Holesky: https://ethereum-holesky.bex.co/<your-api-key>

Layer 2 Networks

Polygon: https://polygon-mainnet.bex.co/<your-api-key>
Arbitrum: https://arbitrum-mainnet.bex.co/<your-api-key>
Optimism: https://optimism-mainnet.bex.co/<your-api-key>

Authentication & Security

API Key Authentication

All requests require your API key in the URL path. Keep your API key secure and never expose it in client-side code.

Rate Limits

Free tier: 100 requests per second
Pro tier: 1,000 requests per second
Enterprise: Custom limits

Best Practices

Use HTTPS for all API calls
Implement retry logic with exponential backoff
Cache responses when appropriate
Monitor your usage in the dashboard
Use batch requests for multiple operations

Common Use Cases

Check Account Balance

javascript

async function getBalance(address) {
  const response = await fetch('https://api.bex.co/harmony/${accessKey}', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({
      jsonrpc: '2.0',
      method: 'eth_getBalance',
      params: [address, 'latest'],
      id: 1
    })
  });
  
  const data = await response.json();
  const balanceWei = BigInt(data.result);
  const balanceEth = balanceWei / BigInt('1000000000000000000');
  return balanceEth.toString();
}

Monitor New Blocks

javascript

// Using WebSocket for real-time updates
const ws = new WebSocket('wss://api.bex.co/harmony/${accessKey}');
 
ws.on('open', () => {
  ws.send(JSON.stringify({
    jsonrpc: '2.0',
    method: 'eth_subscribe',
    params: ['newHeads'],
    id: 1
  }));
});
 
ws.on('message', (data) => {
  const result = JSON.parse(data);
  if (result.params) {
    console.log('New block:', result.params.result);
  }
});

Smart Contract Interaction

javascript

async function callContract(contractAddress, data) {
  const response = await fetch('https://api.bex.co/harmony/${accessKey}', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({
      jsonrpc: '2.0',
      method: 'eth_call',
      params: [
        {
          to: contractAddress,
          data: data
        },
        'latest'
      ],
      id: 1
    })
  });
  
  return await response.json();
}

Error Handling

Common Error Codes

javascript

// Handle RPC errors properly
async function safeRpcCall(method, params) {
  try {
    const response = await fetch(endpoint, {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({
        jsonrpc: '2.0',
        method,
        params,
        id: 1
      })
    });
    
    const data = await response.json();
    
    if (data.error) {
      throw new Error(`RPC Error ${data.error.code}: ${data.error.message}`);
    }
    
    return data.result;
  } catch (error) {
    console.error('RPC call failed:', error);
    throw error;
  }
}

Retry Logic

javascript

async function withRetry(fn, maxRetries = 3) {
  for (let i = 0; i < maxRetries; i++) {
    try {
      return await fn();
    } catch (error) {
      if (i === maxRetries - 1) throw error;
      await new Promise(resolve => setTimeout(resolve, 1000 * Math.pow(2, i)));
    }
  }
}

Next Steps

Explore the [Harmony JSON-RPC API Reference]./harmony-json-rpc-api.md for complete method documentation
Learn about [WebSocket Connections]./harmony-websockets.md for real-time data
Follow our [Web3.js Integration Guide]./harmony-web3-integration.md for frontend development
Check out our [Ethers.js Integration Guide]./harmony-ethers-integration.md for modern development patterns

Resources

Need Help?

📧 Email: hello@bex.co
💬 Discord: Join our community
🐦 Twitter: @BlockEdenHQ
📖 Documentation: docs.bex.co

Cost: 300 CUs / req

Overview​

Quick Start​

Step 1: Get Your API Key​

Step 2: Make Your First Request​

Using cURL​

Using JavaScript (Fetch)​

Using Python​

Core RPC Methods​

Account Information​

Block Information​

Transaction Operations​

Network Endpoints​

Mainnet​

Testnets​

Layer 2 Networks​

Authentication & Security​

API Key Authentication​

Rate Limits​

Best Practices​

Common Use Cases​

Check Account Balance​

Monitor New Blocks​

Smart Contract Interaction​

Error Handling​

Common Error Codes​

Retry Logic​

Next Steps​

Resources​

Need Help?​

One API key for 30+ chains

Overview

Quick Start

Step 1: Get Your API Key

Step 2: Make Your First Request

Using cURL

Using JavaScript (Fetch)

Using Python

Core RPC Methods

Account Information

Block Information

Transaction Operations

Network Endpoints

Mainnet

Testnets

Layer 2 Networks

Authentication & Security

API Key Authentication

Rate Limits

Best Practices

Common Use Cases

Check Account Balance

Monitor New Blocks

Smart Contract Interaction

Error Handling

Common Error Codes

Retry Logic

Next Steps

Resources

Need Help?