Arbitrum One RPC — Free Endpoint & Developer Guide

Arbitrum One is a leading Ethereum layer-2 using optimistic rollups for fast, cheap EVM transactions. This guide shows how to connect to a free Arbitrum One RPC endpoint on MoltNode — no API key and no signup required.

What is Arbitrum One

Arbitrum One is an Ethereum layer-2 network built on optimistic rollup technology. It executes transactions off the Ethereum mainnet and posts the results back to Ethereum for settlement, inheriting Ethereum's security while delivering substantially lower fees and quicker confirmations than the base layer.

Arbitrum One is fully EVM-compatible, so it speaks the standard eth_* JSON-RPC method set, uses ordinary Ethereum-style addresses, and runs the same Solidity contracts and tooling you already know. Like Ethereum, it uses ETH as its native gas token, so there is no separate fee token to manage. The network is identified by chain ID 42161.

Arbitrum One RPC endpoint on MoltNode

MoltNode exposes Arbitrum One at one clean URL that is also a live RPC endpoint:

https://moltnode.ag/arbitrum

There is no API key to provision and no account to create. The endpoint speaks JSON-RPC 2.0 over HTTP POST, and CORS is open so browser-based apps can call it directly. The URL is dual-purpose: a GET request opened in a browser returns a human-readable page about the chain, while a POST carrying a JSON-RPC body returns a machine response. The same address serves both people and programs.

To add it to a wallet, create a custom network with the RPC URL https://moltnode.ag/arbitrum, chain ID 42161, and currency symbol ETH.

Probe it with curl

The fastest way to confirm the Arbitrum One JSON-RPC endpoint is responding is to request the latest block number:

curl -s https://moltnode.ag/arbitrum \
  -X POST \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"eth_blockNumber","params":[]}'

You will get a JSON object with the current block height, hex-encoded, in the result field. Swap in any other standard method — eth_chainId, eth_getBalance, eth_call — to read whatever your app needs.

Use it from your app

Every JSON-RPC client works with the free Arbitrum One RPC. Here is a compact ethers example pointed at the endpoint:

import { JsonRpcProvider } from "ethers";

const provider = new JsonRpcProvider("https://moltnode.ag/arbitrum");

const block = await provider.getBlockNumber();
console.log("Arbitrum block:", block);

The same URL drops into viem, web3.py, wagmi, or any other library that accepts an HTTP RPC URL — no extra configuration beyond the endpoint.

Reliability & failover

The single moltnode.ag/arbitrum URL is backed by more than one upstream provider. Requests are tried in order, and if the first upstream is unreachable or errors out, MoltNode automatically fails over to the next. Upstream API keys are held server-side and never reach your client, so you benefit from premium Arbitrum node reliability without managing any credentials.

There is no hard rate limit, but the endpoint is a shared, free Arbitrum node available to everyone. Use it considerately: cache responses, avoid aggressive polling loops, and for high-volume production workloads, treat MoltNode as a fast default and failover layer rather than a single point of dependence.

For humans and agents

The dual GET/POST design serves developers and automated tools from one place. You can paste https://moltnode.ag/arbitrum into a browser to read about the chain, while a wallet or script POSTs JSON-RPC to the same URL.

For programmatic discovery, MoltNode publishes a machine-readable catalog of every supported chain at https://moltnode.ag/api/chains and an agent-friendly overview at https://moltnode.ag/llms.txt. An AI agent can fetch the catalog, locate the Arbitrum One entry and its endpoint, and begin issuing eth_* calls without any manual setup.

Closing

The free Arbitrum One RPC endpoint at https://moltnode.ag/arbitrum is a no-key, JSON-RPC Arbitrum node ready for viem, ethers, wallets, and AI agents — with automatic failover built in. Point your client at the URL and start building.