Use chain identity in the signing path
eth_chainId reports the chain identifier used by EVM transaction signing. net_version reports a network identifier. They may coincide, but applications should not assume they are interchangeable or use the latter to override a configured signing chain.
Check before a state-changing action
[{"jsonrpc":"2.0","id":"chain","method":"eth_chainId","params":[]},{"jsonrpc":"2.0","id":"network","method":"net_version","params":[]}]The chain result is a hexadecimal quantity, while net_version is normally a decimal string. Convert both explicitly before displaying them. Never compare the raw strings as if different formatting proved a network mismatch.
Keep configuration atomic
- Store chain ID, RPC endpoint and explorer together in a named network configuration.
- At startup, query eth_chainId and compare it with the expected value. Fail closed when they differ.
- Repeat the check when a user changes wallets or an operator changes endpoints.
- Keep testnet credentials, deployment addresses and transaction journals separate from mainnet.
Robinhood example
Robinhood publishes mainnet chain ID 4663 and testnet chain ID 46630. The corresponding hexadecimal values are 0x1237 and 0xb626. These identifiers do not tell you whether a particular token address or contract deployment exists on both networks. Read code and verify deployment metadata on the intended chain before preparing transactions.