Optimism RPC Node: Endpoints, Chain Settings, and Debugging

Quick decision guide: which Optimism RPC option fits your workload?

Before you copy an endpoint into your config, decide what your app actually needs. The right choice depends on request volume, data depth, and whether you need real-time updates.

• Prototyping or low-volume dApps: a public endpoint is fine for testing and light usage, but it can be rate-limited or unstable under load. Use it for development, not production.
• Production apps with moderate traffic: a managed RPC service provides reliability, scalability, and support without the overhead of running your own node. OnFinality offers managed Optimism endpoints with HTTP and WebSocket support.
• High-throughput or data-heavy workloads: if you need archive data, trace methods, or consistent low latency, consider a dedicated node. Dedicated infrastructure gives you isolated resources and avoids noisy-neighbor issues.
• Self-hosted or custom setups: running your own op-node and op-geth gives you full control but requires ongoing maintenance, monitoring, and sync management.

For most teams, a managed RPC service strikes the right balance between cost and reliability. Check RPC pricing and supported networks to see what fits your budget and requirements.

Optimism RPC endpoints at a glance

Optimism (OP Mainnet) is an Ethereum Layer 2 rollup that uses optimistic rollups to scale transactions. It has its own RPC endpoint that follows the Ethereum JSON-RPC standard, plus some OP-specific methods.

Here are the official OnFinality public endpoints for Optimism networks:

These endpoints are public and free to use, but they are shared and may have rate limits. For production, consider a managed or dedicated endpoint.

Chain settings for OP Mainnet and Optimism Sepolia

When adding Optimism to a wallet or configuring your dApp, you need the correct chain settings. Here are the details for both networks:

Use these values when adding the network to MetaMask or other wallets.

Making your first JSON-RPC request

Once you have an endpoint, you can test it with a simple curl command. Here's an example that gets the latest block number:

curl https://optimism.api.onfinality.io/public \
  -X POST \
  -H "Content-Type: application/json" \
  --data '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}'

You should get a response like:

{"jsonrpc":"2.0","result":"0x...","id":1}

For Optimism Sepolia, replace the URL with https://optimism-sepolia.api.onfinality.io/public.

Using Optimism RPC with ethers.js or viem

In your JavaScript application, you can connect to Optimism using ethers.js or viem. Here's an example with ethers.js:

const { ethers } = require("ethers");

const provider = new ethers.JsonRpcProvider("https://optimism.api.onfinality.io/public");

async function getBlockNumber() {
  const blockNumber = await provider.getBlockNumber();
  console.log("Current block number:", blockNumber);
}

getBlockNumber();

With viem:

import { createPublicClient, http } from 'viem';
import { optimism } from 'viem/chains';

const client = createPublicClient({
  chain: optimism,
  transport: http('https://optimism.api.onfinality.io/public')
});

const blockNumber = await client.getBlockNumber();
console.log("Current block number:", blockNumber);

WebSocket subscriptions for real-time data

If your app needs real-time updates, use WebSocket instead of HTTP polling. Here's an example of subscribing to new block headers:

const WebSocket = require('ws');

const ws = new WebSocket('wss://optimism.api.onfinality.io/public');

ws.on('open', function open() {
  ws.send(JSON.stringify({
    jsonrpc: '2.0',
    method: 'eth_subscribe',
    params: ['newHeads'],
    id: 1
  }));
});

ws.on('message', function incoming(data) {
  console.log(data.toString());
});

WebSocket is ideal for applications that need to react to blockchain events instantly, such as transaction monitoring or live dashboards.

Common Optimism RPC failure modes and how to debug them

Even with a reliable endpoint, you may encounter issues. Here are common failure modes and how to diagnose them:

For OP-specific methods, you can use the optimism namespace. For example, optimism_syncStatus returns the current sync status of the node:

curl https://optimism.api.onfinality.io/public \
  -X POST \
  -H "Content-Type: application/json" \
  --data '{"jsonrpc":"2.0","method":"optimism_syncStatus","params":[],"id":1}'

Running your own Optimism node: when it makes sense

Running your own Optimism node gives you full control and eliminates third-party dependencies. You'll need to run both op-node (consensus layer) and op-geth (execution layer). The official docs provide a docker-compose setup for a simple node.

However, self-hosting requires:

• Hardware: a machine with at least 8GB RAM and 1TB SSD (for full node) or more for archive.
• Maintenance: regular updates, monitoring, and handling sync issues.
• Network: a stable, high-bandwidth connection.

If you have the expertise and need custom infrastructure, self-hosting is viable. Otherwise, a managed service like OnFinality's dedicated nodes can save time and effort.

How to choose between public, managed, and dedicated Optimism RPC

When evaluating Optimism RPC providers, consider these factors:

• Reliability: Look for providers with a track record of uptime and low latency. OnFinality offers managed endpoints with monitoring and failover.
• Scalability: Ensure the provider can handle your request volume without rate limiting. Dedicated nodes offer isolated resources.
• Data depth: If you need historical data, check if the provider offers archive nodes. OnFinality supports archive data for Optimism.
• WebSocket support: For real-time apps, confirm the provider supports WebSocket connections.
• Pricing: Compare costs based on your expected usage. OnFinality's pricing is transparent and flexible.

For a detailed comparison of RPC providers, see our guide on choosing an RPC provider.

Key Takeaways

• Optimism RPC endpoints follow Ethereum JSON-RPC, so you can use familiar tools and libraries.
• Public endpoints are fine for development, but production apps should use managed or dedicated infrastructure.
• Always verify chain settings (chain ID, explorer) when adding Optimism to your wallet or app.
• Use WebSocket for real-time data and implement reconnection logic for resilience.
• Debug common issues by checking sync status, reducing query ranges, and using state overrides.
• OnFinality provides reliable Optimism RPC endpoints with HTTP and WebSocket support, plus dedicated node options.

Frequently Asked Questions

What is an Optimism RPC node?

An Optimism RPC node is a server that allows you to interact with the Optimism network via JSON-RPC calls. It lets you read blockchain data, send transactions, and subscribe to events.

How do I get an Optimism RPC endpoint?

You can use a public endpoint like https://optimism.api.onfinality.io/public for testing, or sign up for a managed service to get a private endpoint with higher limits.

What is the chain ID for Optimism?

OP Mainnet has chain ID 10, and Optimism Sepolia has chain ID 11155420.

Can I use Optimism RPC with ethers.js?

Yes, ethers.js and viem both support Optimism out of the box. You just need to provide the RPC URL.

What is the difference between a full node and an archive node?

A full node stores the entire blockchain state but prunes historical state. An archive node stores all historical state, allowing queries at any past block. Archive nodes are useful for analytics and debugging.

How do I debug a failed transaction on Optimism?

Use eth_call with stateOverride to simulate the transaction and see the revert reason. Also check the nonce and gas settings.

Does OnFinality support Optimism Sepolia?

Yes, OnFinality provides public and managed endpoints for Optimism Sepolia. See the Optimism network page for details.

What are the rate limits for public Optimism RPC endpoints?

Public endpoints have rate limits to ensure fair usage. For production, consider a managed or dedicated endpoint to avoid hitting these limits.

How can I monitor my Optimism RPC usage?

Most managed providers offer dashboards to monitor request volume, latency, and errors. OnFinality provides usage analytics for your endpoints.

Can I run my own Optimism node?

Yes, you can run your own node using the official docker-compose setup. However, it requires technical expertise and ongoing maintenance.

For more details on Optimism RPC and infrastructure, visit our Optimism network page or explore supported networks.