Supported Chains

web3agent supports 17 EVM-compatible chains out of the box. Every chain ships with a built-in public RPC endpoint so you can get started without any additional configuration. Blockscout indexer support is available on 8 of those chains, unlocking the full suite of explorer tools.

Chain Reference

Chain	Chain ID	Default RPC	Blockscout Support
Ethereum	1	Yes	Yes
Base	8453	Yes	Yes
Arbitrum	42161	Yes	Yes
Optimism	10	Yes	Yes
Polygon	137	Yes	Yes
Linea	59144	Yes	No
BSC	56	Yes	No
Avalanche	43114	Yes	No
zkSync Era	324	Yes	Yes
Scroll	534352	Yes	Yes
Mode	34443	Yes	No
Blast	81457	Yes	No
Mantle	5000	Yes	No
Celo	42220	Yes	No
Gnosis	100	Yes	Yes
Sepolia	11155111	Yes	No
Base Sepolia	84532	Yes	No

Base (8453) is the default chain. All tools that accept a chainId parameter will use Base unless you specify otherwise.

Blockscout-Enabled Chains

The following 8 chains have full Blockscout indexer support, which powers the blockscout_* family of explorer tools (address info, transaction history, token transfers, contract ABIs, NFT metadata, and more):

• Ethereum (1)
• Base (8453)
• Arbitrum (42161)
• Optimism (10)
• Polygon (137)
• Gnosis (100)
• Scroll (534352)
• zkSync Era (324)

On chains without Blockscout support, the evm_* tools still work for live on-chain reads (balances, contract calls, gas estimation), but indexed historical data is not available.

Configuring the Default Chain

Environment variable

Set CHAIN_ID in your environment to change the global default:

CHAIN_ID=42161  # Use Arbitrum as default

Per-call override

Most tools and SDK functions accept a chainId parameter that overrides the default for that specific call:

import { getSwapQuote } from "web3agent";

const quote = await getSwapQuote({
  fromToken: "0x...",
  toToken: "0x...",
  fromAmount: "1000000",
  chainId: 42161,  // Arbitrum, regardless of CHAIN_ID env var
});

Custom RPC endpoint

To use a private or faster RPC for the default chain, set RPC_URL:

RPC_URL=https://mainnet.infura.io/v3/YOUR_KEY
CHAIN_ID=1

RPC_URL applies only to the chain specified by CHAIN_ID. For other chains, the built-in public RPCs are used.

Chain Resolution

Two SDK functions let you look up chain metadata programmatically:

import { getChain, findChainByName } from "web3agent";

// Look up by numeric ID
const base = getChain(8453);
// { id: 8453, name: "Base", nativeCurrency: { symbol: "ETH", decimals: 18 }, ... }

// Look up by name (case-insensitive)
const arb = findChainByName("arbitrum");
// { id: 42161, name: "Arbitrum One", ... }

Both functions return undefined if the chain is not found, so check the return value before using it.

Testnets

Sepolia (11155111) and Base Sepolia (84532) are included for development and testing. They behave identically to mainnet chains from the API perspective, but Blockscout indexer support is not available on either testnet.

Testnet chains use test ETH with no real value. Make sure CHAIN_ID is set correctly before executing any write operations.