ChainID opcode

The five-minute read

One action, walked through

1. Open EIP 1344 and read the status line before the examples.
2. Write down the rule in one sentence. A fair version of that sentence is: An opcode that returns the current chain's EIP-155 unique identifier.
3. Name the object that changes: CHAINID.
4. Ask what an old client, an old contract, or an offline counterparty does. If the document is silent, the silence is part of the design.

The argument, unpacked

What has to be true

• You are implementing EIP 1344 at the status the text itself states: Final.
• The object that has to change is CHAINID. A neighbouring document with a similar name is not this one.
• Constants in the text can be superseded by a later fork. Cite the EIP number and the fork you mean.

What happened after the paper

The source marks this final. That is a statement about the text, not a promise that every wallet or node has shipped it. Later documents can narrow, replace, or ignore this one. Cite the number you mean.

What to check before you use the idea

• What does ChainID opcode charge, reject, or redefine on the first touch versus a later one?
• Does a reverted subcall roll the change back?
• Can you point at the object in a client: CHAINID?

Terms

EIP 1344

The public text titled ChainID opcode.

Final

The document's own label for how finished the text is. It is not a market fact.

The problem the paper names

An underpriced or ambiguous EVM rule is not a feature. It is a block that takes longer than the gas limit claimed, or a client that disagrees about the result.

What the design proposes

• An opcode that returns the current chain's EIP-155 unique identifier.
• EIP-155 proposes to use the chain ID to prevent replay attacks between different chains.
• It would be a great benefit to have the same possibility inside smart contracts when handling signatures, especially for Layer 2 signature schemes using EIP-712.

How the mechanism is specified

• Taken from the specification, the next constraint is: EIP-155 proposes to use the chain ID to prevent replay attacks between different chains.
• Locate CHAINID in EIP 1344 and apply it to one transaction or call.
• Then check the failure the class of rule always has: a node that did not upgrade, a reverted call, a replayed signature, or a peer that does not speak the message.

What this page does not treat as proven

• A gas or opcode change is not a throughput benchmark. It is a relative price and a validity rule.
• Constants in the text can be superseded by a later fork. Cite the EIP number and the fork you mean.
• The source marks this final. That is a statement about the text, not a promise that every wallet or node has shipped it.

Why a venture studio still reads it

Use EIP 1344 when a pitch says 'ChainID opcode' without saying whether the rule is consensus, policy, or an interface. The number is the citation. The pitch is not.