How to Use a Blockchain API
Author: Uttam Singh
Unlock the power of blockchain without writing a single line of low‑level code. This guide shows you exactly how to use a blockchain API—from fundamentals to practical implementation so you can launch on‑chain applications faster, cheaper, and with confidence.
Why the Right API Matters More Than the Blockchain Itself
Imagine you’re building a decentralized finance (DeFi) app, a launchpad, or a supply‑chain tracking system. The most powerful component of your stack isn’t the front‑end UI, the database, or even the smart contracts. It's the bridge that connects your app to the blockchain: the blockchain API.
A good API turns a complex, distributed network into a single, predictable interface, normalized data, real‑time streams, smart retries and failover. It hides node ops, consensus quirks, and edge cases so you ship features while it handles node uptime, consensus oddities, and scale.
In this blog post, we’ll cover what a blockchain API is, how it helps you build on‑chain applications, and how to use them
1. What Exactly Is a Blockchain API?
A blockchain API is a set of programmatic interfaces (usually HTTP/REST, WebSocket, or RPC) that expose blockchain data, such as reading block data, querying balances, submitting transactions, or listening for events, over a standardized, developer‑friendly layer.
Think of it as remote-controlled blockchain access. Instead of running your own Bitcoin or Ethereum node directly, you call an API endpoint and get the same data you’d get from the node, without the overhead of syncing and maintaining the node yourself.
Key Components
These components together let you read, write, and listen to any blockchain that the API provider supports, whether that’s Ethereum, Solana, or every chain in between.
On‑Chain vs. Off‑Chain: Where the API Lives
One important thing to remember is that a blockchain is an onchain database. However, a blockchain API is an offchain service that queries or writes to that onchain database.
In other words, the API is your app’s gateway to the blockchain, enabling you to interact with onchain data, transact with onchain users, and write new data to the network.
How a Blockchain API Helps You Build Onchain Applications
Even if you’re running your own node, you will still need to use the node’s API to connect to the blockchain. Without a blockchain API, your app can’t interact with, or react to, anything happening on the network. Hard to build an app without that.
But when people hear the phrase “blockchain API,” they are often referring to 3rd party providers that run nodes and infrastructure for other teams, so all you have to do is interact with a simple API to get the read/write data you need for your application. These services, like those we provide at Alchemy, offer a number of additional benefits, beyond the simple functionality they provide.
Speed to Market
Running a full blockchain node can take days to sync, requires constant hardware resources, and demands constant updates. It can be a significant burden for your team, particularly when operating at scale. A blockchain API eliminates these headaches, letting you:
Launch in days, not weeks
Scale instantly with the provider’s infrastructure
Focus on your customers, product features, UX, and business logic, and not on network connectivity and uptime
Cost Efficiency
Running a high‑availability node is costly. It’s not as simple as spending a week syncing your node, and then your off to the races. Nodes crash. Nodes are inefficient for a number of data queries. If you’re operating at scale, you need a node fleet, optimized databases, intelligent routing, and a thousand other infrastructure optimizations and layers in order to serve millions of customers at scale. That translates to bare metal costs and a lot of engineering resources.
Rather than build all of that out yourself, you can just use a blockchain API provider, many of which, Alchemy included, offer pay-as-you-go plans, so you’re only paying for the compute and resources you need.
Reliability and Security
Professional API providers also provide a lot of features to improve reliability and security that you don’t even need to think about, apart from knowing that they deliver you 99.99% uptime and a highly reliable connection to a blockchain network, even during network spikes. That includes work like DDoS mitigation, rate limiting, load balancing, and continuous node health monitoring.
Multichain Access
Instead of learning each network’s RPC endpoints, and data config, with a single provider, you can swap chains while using a single API key, with endpoints returning data in the same format, simplifying your codebase and making it much easier to go multichain.
Selecting the Right Blockchain API Provider
Core Criteria for API Evaluation
When picking a blockchain API provider, here are some criteria you should be thinking about when comparing various services:
The good news is that there are a lot of blockchain API providers you can choose from, so you can find whatever mix of reliability, cost, and features you need for your app.
Step‑by‑Step Guide: How to Use a Blockchain API
Below is the exact workflow to get from zero to fully‑integrated blockchain API. Follow each step, and you’ll be able to run a live on‑chain query within 2 minutes.
Step 1: Choose a Provider & Register
Sign up for an account at the provider’s dashboard (e.g., https://dashboard.alchemy.com).
Verify your email and set up 2‑factor authentication (security best practice).
Navigate to “Create App” or “Project.” Give it a clear name (e.g., “MyDeFi‑API‑Prod”) to separate dev/prod.
Step 2: Grab Your API Key (or JWT)
In the dashboard, locate “API Key” or “Token”.
Copy the key and store it in a secure vault (e.g., HashiCorp Vault, AWS Secrets Manager). Never hard‑code the key in your repo.
Step 3: Test a Simple “Get Latest Block” Call
Using cURL (raw REST) and your Alchemy API key, you can test a simple API call:
curl -X POST <https://eth-mainnet.g.alchemy.com/v2/{apiKey}> \\
-H "Content-Type: application/json" \\
-d '{
"jsonrpc": "2.0",
"method": "eth_getBlockByNumber",
"params": [
"latest",
false
],
"id": 1
}'You can also use the Viem library. To install viem, use the command: npm i viem
//npm i viem
import { createPublicClient, http } from "viem";
import { mainnet } from "viem/chains";
const client = createPublicClient({
chain: mainnet,
transport: http("<https://eth-mainnet.g.alchemy.com/v2/>{API KEY}"),
});
const block = await client.getBlock()
console.log(block);You should see the latest Ethereum mainnet block: the API is working!
Step 4: Build a Core Use Case (e.g., Read an ERC‑20 Balance)
// npm i viem
import { createPublicClient, http, formatUnits, getContract } from "viem";
import { mainnet } from "viem/chains";
import { erc20Abi } from "viem"; // minimal ERC-20 ABI
const client = createPublicClient({
chain: mainnet,
transport: http("<https://eth-mainnet.g.alchemy.com/v2/YOUR_API_KEY>"),
});
const tokenAddress = "0x6B175474E89094C44Da98b954EedeAC495271d0F"; // DAI
const walletAddress = "{WalletAddress}";
const dai = getContract({
address: tokenAddress,
abi: erc20Abi,
client,
});
async function getBalance() {
const [balance, decimals] = await Promise.all([
dai.read.balanceOf([walletAddress]), // returns bigint
dai.read.decimals(), // returns number
]);
console.log(`Balance: ${formatUnits(balance, decimals)} DAI`);
}
getBalance();Now you’ve read a token balance using a blockchain API, no node needed. Pretty cool.
Step 5: Set Up Webhooks / Real‑Time Events
Alongside a simple REST API, many providers also allow Webhooks or WebSocket subscriptions, which are useful for notifications and streaming block data respectively.
Example: Listen for new blocks
// npm i ws
const WebSocket = require('ws');
const ws = new WebSocket('wss://eth-mainnet.g.alchemy.com/v2/{API KEY}');
ws.on('open', () => ws.send(JSON.stringify({
jsonrpc: '2.0', id: 1, method: 'eth_subscribe', params: ['newHeads']
})));
ws.on('message', (d) => {
const m = JSON.parse(d);
if (m.method === 'eth_subscription') {
console.log('New block:', BigInt(m.params.result.number));
}
});Step 6: Deploy to Production & Monitor
Rate‑limit check: Ensure you stay within your plan’s request quota (e.g., 100 req/s).
Enable alerts: Most dashboards have usage dashboards; set alerts for spikes.
Logging: Capture request/response latency for performance tuning.
Fallback: Keep a secondary provider in case of an outage.
Best Practices & Common Pitfalls
Security Measures
Blockchains are ripe for hacks and exploits, no surprise when you think about how much money flows through the network. But as a result, you need to be particularly mindful of security.
When it comes to API key security, you want to make sure you follow a number of best practices to secure your application. Those practices include taking actions like:
Rotate API keys regularly (e.g. every 90 days) to reduce exposure to key leakage
Use IP whitelisting to prevent unauthorized usage
Encrypt secret storage to protect your keys at rest
Validate responses to avoid malicious payloads
Performance Optimizations
API calls can also be expensive. As you scale, you may want to optimize how your app interacts with the blockchain API. Some example optimizations include:
Batch requests: Many APIs support
eth_batchor GraphQL queries to reduce round-tripsCache read-only data: Cache token balances for a short TTL (e.g. 30 seconds) to lower request volume
Use WebSockets for events: Pull-polling wastes resources when push events can be more efficient
Real‑World Use Cases: Where Companies Leverage Blockchain APIs Today
These examples show that the same API can power consumer‑facing marketplaces, high‑frequency finance, and enterprise—all with the same blockchain API under the hood.
Actionable Takeaways
Pick a provider that matches your chain and performance requirements.
Secure your API key using secret management and rotate it regularly.
Start with a simple query (e.g., block number) to verify connectivity.
Implement caching and batch requests to stay within quotas and improve performance.
Use Webhooks/WebSockets for real‑time events rather than polling.
Set up monitoring (alerts, dashboards) for usage, latency, and error tracking.
Test in a sandbox before moving to production; keep a fallback provider ready.
Start Building Onchain Faster Than Ever
A reliable blockchain API is the single most powerful tool you can add to a modern developer’s toolbox. By abstracting the heavy lifting of node operation, it lets you focus on your customers, your product value, and revenue‑generating features.
Now you know how to use a blockchain API, are you ready to try one out? Make an Alchemy account and make your first API call from our dashboard. Get started.
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