ERC-8021 Builder Code Validator
Builder Codes and EIP-8021 solve onchain attribution by appending standardized data suffixes to transaction calldata, linking apps to transactions for verifiable tracking.
What is ERC-8021?
ERC-8021 is a transaction attribution standard that allows apps and builders to embed attribution data directly into onchain transactions. It uses a data suffix appended to transaction calldata, enabling ecosystems to identify which app or builder generated a transaction without modifying smart contracts.
ERC-8021 leverages an underutilized EVM property: smart contracts ignore extra data appended beyond their expected function arguments. A "data suffix" is appended to the end of transaction calldata, passing through execution without any impact on the contract's behavior. The suffix is parsed backwards — first the 16-byte marker, then the schema ID, then the schema-specific data.
ERC-8021 works on any EVM-compatible blockchain. It was pioneered on Base and is supported across Ethereum L1, Optimism, Arbitrum, and other EVM chains. Since it only appends data to calldata, no special chain support is needed.
What are Builder Codes?
Builder Codes are unique identifiers (like "baseapp" or "formo") registered through a Code Registry smart contract. They link onchain transactions to the apps and builders that generated them, enabling ecosystems to measure and reward builders for the value they create.
ERC-8021 supports multiple comma-separated builder codes in a single attribution suffix. This is useful when a transaction is facilitated by multiple builders — for example, a frontend app and a backend relay service.
Learn more: https://formo.so/blog/builder-codes-erc-8021-explained
Your questions, answered
Find answers to frequently asked questions below.
What is ERC-8021?
How does ERC-8021 work?
What are Builder Codes?
What is the difference between Schema 0 and Schema 1?
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How do I register a Builder Code?
Can a transaction have multiple Builder Codes?
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