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Networks and chain IDs: verify before you add a custom network

What a chain ID and RPC are, why fake custom-network prompts are dangerous, and how to verify against official docs before adding—MetaMask and ethereum.org literacy, not investment advice.

A wallet does not “contain” the blockchain. It asks a node for balances, pending status, and to broadcast signed transactions. That ask usually goes over a remote procedure call (RPC) endpoint—an HTTPS (or similar) URL that speaks a standard API. According to ethereum.org’s JSON-RPC documentation, software must connect to a node to read chain data or send transactions, and clients implement a shared JSON-RPC specification so apps can use uniform methods. Literacy here is about which network and which URL you trust—not which asset to buy.

How it works: networks, chain IDs, and RPCs

ethereum.org’s networks page describes networks as groups of computers that share a protocol. There is one Ethereum Mainnet; separate networks can follow similar rules without sharing balances or history. Your account address may look the same across EVM-style networks, but balances and transaction history do not carry over.

When you sign a transaction, the wallet embeds a chain ID—an identifier that helps keep a signature from being replayed on the wrong network. ethereum.org’s JSON-RPC docs list eth_chainId as returning the chain ID used for signing replay-protected transactions, and note common network IDs such as 1 for Ethereum Mainnet and 11155111 for the Sepolia testnet (always re-check primary docs; do not copy IDs from strangers).

MetaMask’s Help Center defines RPC as the set of protocols that let a client (such as the wallet) interact with a blockchain, and explains that you can add a custom network manually or add additional RPC URLs for a network you already use—see How to add a network. Other wallets use the same idea with different menus. Optional literacy: Ethereum and PulseChain are separate networks; if you add either (or any other), treat name, chain ID, RPC URL, and explorer as a matched set from that network’s official documentation—not from a DM.

How to verify before you approve “Add network”

Sites can prompt wallets to add a custom network. MetaMask’s verification guide is clear: the wallet may run basic checks and warn about oddities, but it does not verify custom networks. Even when validation “looks fine,” the network can still be malicious or misrepresented. Trust the prompt only as much as you trust the site that opened it.

The confirmation typically shows fields such as network name, network URL (RPC), chain ID, currency symbol, and optional block explorer URL. Before you approve:

  1. Open the network’s official documentation yourself (typed or bookmarked)—not a link from a chat, ad, or “support” DM. Compare chain ID, RPC hostname, symbol, and explorer character-for-character.
  2. Reject pressure: a real literacy flow can wait while you read. Fake prompts create urgency (“claim,” “migrate,” “fix assets”) so you skip the comparison.
  3. Prefer adding from wallet settings using values you copied from official docs over approving a surprise popup from an unfamiliar page.
  4. After adding, confirm a known read (e.g. your address on an explorer you opened yourself) matches what the wallet shows—pair with how to read a transaction.
  5. If anything mismatches or you cannot find official docs, reject the add and research later. MetaMask’s guide says the same: when unsure, reject and try again only after more research.

What we will not do

We will not recommend which network to use, which RPC provider to pay for, or which tokens to hold on any chain. We will not publish “canonical” RPC URLs or chain IDs as investment tips—only the habit of verifying against primary educational and wallet docs.

TakeawayAn “Add network” prompt is a trust decision: the wallet connects to whatever RPC and chain ID you accept. Verify name, chain ID, RPC URL, and explorer from official docs you opened yourself—or decline.

Related free docs

Sources

Educational content only — not investment advice. This page explains how wallets connect via RPC and how to verify network-add details; it does not recommend any network, provider, or asset to buy or sell.

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