What are Builder Codes? Builder codes are app identifiers defined by the ERC-8021 standard that are appended to transaction calldata, allowing any onchain transaction to be attributed to the app or builder that generated it.
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Builder codes bring that idea onchain. An app appends a small identifier to the end of each transaction it generates. The transaction executes exactly as normal, but anyone can later read the code and see which app produced it.
ERC-8021 standardizes this, so attribution works across apps and chains without modifying any smart contracts. It also enables a registry where builders map their codes to wallet addresses, letting platforms share revenue with the apps that drive their volume.
What Builder Codes Mean For Audience
Use Case
App builders and frontends
Tag the transactions their interfaces generate to prove the volume they drive and qualify for ecosystem rewards
Protocols and platforms
Identify which apps and integrations generate their transaction volume and reward builders accordingly
Growth and analytics teams
Use builder codes as a native onchain attribution signal alongside UTM and wallet-based attribution
Examples A swap interface appends its builder code to every transaction it generates, making its contribution to a DEX's volume verifiable onchain.
An ecosystem launches a rewards program that distributes fees to builders based on the transaction volume attributed to their codes.
A protocol analyzes builder codes on incoming transactions to learn which third-party interfaces drive its most valuable users.
A developer registers their builder code in the onchain registry, mapping it to a wallet address that receives revenue-share payouts.
FAQs What is ERC-8021? ERC-8021 is an Ethereum standard for transaction attribution. It defines how apps append a structured data suffix containing a builder code to transaction calldata so the transaction's origin can be identified.
Do builder codes require changes to smart contracts? No. The attribution data sits at the end of calldata and is ignored by the contract during execution. Indexers and registries parse it afterward, so existing contracts work without modification.
Why do builder codes matter for attribution? They make attribution native to the transaction itself. Instead of inferring which app generated a transaction from offchain signals, the answer is recorded onchain and verifiable by anyone.
Which chains support builder codes? ERC-8021 works on any EVM-compatible chain. The pattern was popularized on Base and applies across Ethereum and other EVM networks.
How do builders earn from builder codes? A registry contract maps builder codes to payout addresses. Platforms running revenue-share or rewards programs use attributed volume to distribute earnings to those addresses.