Blockchain networks FAQ and glossary

A Remote Procedure Call (RPC) URL is the HTTPS or WebSocket endpoint a wallet or dapp sends JSON RPC requests to. Every blockchain has many possible RPC URLs — some run by the foundation, some by paid providers like Alchemy or QuickNode, some by community projects. You can swap them out without changing your wallet address.

A chain ID is a unique numeric identifier that distinguishes one EVM network from another. Defined by EIP 155 and reported by the eth_chainId JSON RPC method, it is part of every signed transaction so a tx mined on Ethereum (chain ID 1) cannot be replayed on Polygon (137). Cosmos SDK chains use string chain ids like cosmoshub-4 instead.

Public RPCs are free, anonymous, and shared — fine for development and wallet reads, rate limited under load. Paid RPCs give you a private API key, higher throughput, archive history, websockets, and SLA backed availability. Use the public one as a fallback once you have paid in place.

EIP 3085 standardises the wallet_addEthereumChain JSON RPC method. A dapp can ask the user to add a new network with one prompt by passing a JSON payload with chainId, chainName, nativeCurrency, rpcUrls, and blockExplorerUrls. MetaMask, Rabby, OKX Wallet, Brave Wallet, and Frame all implement it.

An archive node retains the full historical state of the chain — every account balance and contract storage slot at every block — not just the latest. You need an archive endpoint to query an account balance two years ago, replay a transaction, or backfill an indexer. Archive data is much larger than the latest state, which is why paid providers charge more for it.

A WebSocket RPC endpoint (URL starts with wss://) keeps a persistent connection open so the chain can push events to your dapp as they happen — new blocks, pending transactions, log emissions for an eth_subscribe filter. HTTP polling works for low frequency reads; WebSockets are what real time UIs and trading bots use.

Finality is the point at which a transaction is irreversible. Ethereum has economic finality after one slot and full Casper finality after roughly 12.8 minutes (two epochs). Optimistic rollups like Arbitrum and OP Mainnet are soft confirmed quickly but final on Ethereum after the seven day challenge window. ZK rollups finalise once their proof is verified, usually within hours.

EIP 1559 changed Ethereum gas pricing from a first price auction to a base fee plus priority tip. The base fee is burned, the tip goes to the validator, and the protocol adjusts the base fee per block based on demand. Most EVM chains have adopted it, which is why MetaMask shows max fee and max priority fee fields instead of a single gas price.

On a rollup like Arbitrum, OP Mainnet, Base, Linea, ZKsync Era, or Blast, the sequencer is the entity that orders incoming transactions and posts them to Ethereum. At launch most rollups operate a centralised sequencer. Decentralised sequencing (Espresso, Shutter, shared sequencers) is in progress across the ecosystem.

Maximal Extractable Value (MEV) is the profit a block producer can extract by reordering, inserting, or censoring transactions in a block — common examples include sandwich attacks on DEX trades and arbitrage between pools. Private mempool RPCs (Flashbots Protect, MEV Blocker) hide your tx from public mempools to mitigate sandwich risk.

Three common causes: (1) The RPC URL the wallet is talking to actually serves a different chain (some testnet RPCs reuse a mainnet chain ID by mistake). (2) The dapp pinned a chain ID and the wallet is on a different one — check window.ethereum.chainId. (3) Cached state from a previous session — force a reload after switching networks.

Indexers need archive history, generous eth_getLogs limits, and ideally trace methods. Public RPCs rate limit those aggressively. Chainstack, QuickNode, Alchemy (Trace API), and Tenderly are common picks. Reserve the public endpoint as a fallback for read traffic from end users, not for the indexer itself.