Substrate Explorer API

Selendra's Substrate layer can be queried programmatically using the WebSocket RPC API or the Polkadot.js SDK. This allows access to the native chain state, governance, staking, and other Substrate-specific features.

Overview

Unlike the EVM Explorer (Blockscout) which provides a REST API, the Substrate Explorer (Polkadot.js) interacts directly with the blockchain nodes via WebSocket or HTTP RPC.

Interface: Selendra Portal
RPC Endpoint: wss://rpc.selendra.org
HTTP Endpoint: https://rpc.selendra.org

Connecting via Polkadot.js API

The easiest way to interact with the Substrate API is using the @polkadot/api library.

Installation

npm install @polkadot/api

Basic Connection

import { ApiPromise, WsProvider } from '@polkadot/api';

async function main() {
  // Initialise the provider to connect to the local node
  const provider = new WsProvider('wss://rpc.selendra.org');

  // Create the API and wait until ready
  const api = await ApiPromise.create({ provider });

  // Retrieve the chain & node information via rpc calls
  const [chain, nodeName, nodeVersion] = await Promise.all([
    api.rpc.system.chain(),
    api.rpc.system.name(),
    api.rpc.system.version()
  ]);

  console.log(`You are connected to chain ${chain} using ${nodeName} v${nodeVersion}`);
}

main();

Common API Queries

Get Block Information

// Get the latest block hash
const lastBlockHash = await api.rpc.chain.getFinalizedHead();

// Get the block data
const block = await api.rpc.chain.getBlock(lastBlockHash);

console.log(`Latest block number: ${block.block.header.number}`);
console.log(`Block hash: ${lastBlockHash}`);

Query Account Balance

const ADDR = '5GrwvaEF5zXb26Fz9rcQpDWS57CtERHpNehXCPcNoHGKutQY';

// Retrieve the account balance & nonce via the system module
const { nonce, data: balance } = await api.query.system.account(ADDR);

console.log(`Balance: ${balance.free} and nonce: ${nonce}`);

// Subscribe to the new headers
const unsub = await api.rpc.chain.subscribeNewHeads((header) => {
  console.log(`New block #${header.number} has hash ${header.hash}`);
});

RPC Methods

You can also interact with the node using standard JSON-RPC calls if you are not using the JavaScript SDK.

Get Chain Info

Request:

curl -H "Content-Type: application/json" -d '{"id":1, "jsonrpc":"2.0", "method": "system_chain", "params":[]}' https://rpc.selendra.org

Response:

{
  "jsonrpc": "2.0",
  "result": "Selendra Mainnet",
  "id": 1
}

Get Block Hash

Request:

curl -H "Content-Type: application/json" -d '{"id":1, "jsonrpc":"2.0", "method": "chain_getBlockHash", "params":[0]}' https://rpc.selendra.org

Key Substrate Concepts

Storage Queries

Substrate storage is defined in the runtime modules (pallets). You can query any storage item using api.query.<module>.<item>.

api.query.system.account(address): Account info
api.query.staking.validators(): List of validators
api.query.timestamp.now(): Current block timestamp

Extrinsics (Transactions)

Transactions in Substrate are called "extrinsics".

// Create a transfer extrinsic
const transfer = api.tx.balances.transfer(recipient, amount);

// Sign and send the transaction
const hash = await transfer.signAndSend(sender);

Additional Resources

EVM Explorer API

Use Cases

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