eth_chainId

eth_chainId returns the chain ID of the connected network as a hex-encoded integer. On Polygon mainnet this is the constant 0x89 (137 decimal). It is the cheapest possible call against the Polygon RPC surface — one request resolves to a single immutable constant — which makes it a common liveness ping.

Its primary purpose is EIP-155 replay protection: the chain ID is mixed into the transaction signature so that a transaction signed for Polygon cannot be replayed on another EVM chain. Wallets and signing libraries call it once before constructing a transaction. Because the value never changes for a given network, clients should fetch it once per connection and cache it indefinitely (TTL = ∞).

This method belongs to the free polygon_read_rpc category, so it is available on every tier starting at Free. It takes no parameters. If you are targeting the Polygon Amoy testnet instead of mainnet, the returned value is 0x13882 (80002 decimal).

Note: net_version returns the same chain identity as a decimal string ("137") rather than a hex quantity. Prefer eth_chainId for EIP-155 and modern signing flows; net_version exists mainly for legacy Web3.js (< 4.x) chain detection.

This method takes no parameters. Pass an empty params array.

Response fields

Errors follow the standard JSON-RPC error envelope. See the shared errors reference for the full error.data shape (current_tier, required_tier, limit_rps, retry_after_sec, upgrade_url, …).

JavaScript (fetch)

const res = await fetch("https://api.triport.io/v1/polygon", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.TRIPORT_API_KEY}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    jsonrpc: "2.0",
    id: 1,
    method: "eth_chainId",
    params: [],
  }),
});


const { result } = await res.json();
const chainId = parseInt(result, 16); // 137
console.log(`Connected to Polygon chain ${chainId}`);

TypeScript SDK (@triport/sdk)

import { TriportClient } from "@triport/sdk";


const client = new TriportClient({
  apiKey: process.env.TRIPORT_API_KEY!,
  network: "polygon",
});


const chainId = await client.rpc<string>("eth_chainId");
console.log(parseInt(chainId, 16)); // 137

Python (triport-sdk)

import os
from triport import TriportClient


client = TriportClient(
    api_key=os.environ["TRIPORT_API_KEY"],
    network="polygon",
)


chain_id_hex = client.rpc("eth_chainId")  # "0x89"
print(int(chain_id_hex, 16))             # 137

• Cache aggressively. The chain ID is immutable per network — fetch it once per connection and reuse it. There is no need to re-poll.
• Mainnet vs testnet. 0x89 = Polygon mainnet (137); 0x13882 = Polygon Amoy testnet (80002). Always confirm you are signing for the chain you intend.
• EIP-155. Pass the decoded integer (137) as the chainId field when constructing and signing transactions to enable cross-chain replay protection.
• Related methods: net_version (same identity, decimal string), eth_blockNumber (chain liveness/tip), web3_clientVersion (node client string).