Glossary: Builder Codes (ERC-8021)

What are Builder Codes?

Builder codes use the ERC-8021 format to associate supported EVM transactions with the app or builder that constructed them. They provide transaction-level provenance and complement, rather than replace, campaign and referral attribution.

Builder Codes Explained

When you buy something online through an affiliate link, the retailer knows which website sent you, and that website earns a commission.

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

1. A swap interface appends its builder code to every transaction it generates, making its contribution to a DEX's volume verifiable onchain.

2. An ecosystem launches a rewards program that distributes fees to builders based on the transaction volume attributed to their codes.

3. A protocol analyzes builder codes on incoming transactions to learn which third-party interfaces drive its most valuable users.

4. A developer registers their builder code in the onchain registry, mapping it to a wallet address that receives revenue-share payouts.

Related reading

Explore Onchain Attribution, Transaction, EIP (Ethereum Improvement Proposal), and Smart Contract Events.

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.