Ethereum Attestation Service (EAS)

The Ethereum Attestation Service (EAS) is a permissionless, schema-based protocol for creating, managing, and verifying attestations on any EVM-compatible blockchain. An attestation is a structured, digitally signed piece of data that makes a claim about anything—a person's identity, a credential, the outcome of a vote, or the authenticity of a piece of content. By providing a standardized, gas-efficient, and chain-agnostic framework, EAS acts as foundational infrastructure for decentralized identity, reputation systems, on-chain voting, and verifiable credentials, enabling trustless verification of arbitrary claims without a central authority.

At its core, EAS operates through two primary smart contracts: the Schema Registry and the Attestation Registry. First, a user defines a schema, which is a template that structures the data of an attestation (e.g., field names and types for a diploma or a product review). Once a schema is registered on-chain, anyone can create an attestation against it. This attestation is a transaction that records the claim's data, the identities of the attester (issuer) and recipient (subject), and a revocation status, all hashed and signed for cryptographic integrity. This design separates the data structure from the attestation logic, providing immense flexibility.

A key innovation of EAS is its support for both on-chain and off-chain attestations. On-chain attestations store the data directly on the blockchain, providing maximum transparency and immutability but incurring gas costs. Off-chain attestations are signed JSON objects (like EIP-712 signatures) that can be stored anywhere (e.g., IPFS or a server), with only a minimal cryptographic commitment posted on-chain. This hybrid model allows for cost-effective scaling and privacy, where sensitive data can remain off-chain while its authenticity is verifiable against the chain. All attestations can be revoked or timestamped by their original attester, enabling dynamic data management.

The protocol's utility is amplified by its schema marketplace and composability. Developers can create and share public schemas for common use cases—like event tickets, KYC verifications, or skill badges—which others can freely adopt. This fosters interoperability across applications. Furthermore, because attestations are simple, standard data structures, they are highly composable. A user's attestations from one dApp (like a DAO membership) can be seamlessly read and utilized by another unrelated dApp (like a lending protocol) to build complex, cross-application reputation graphs and conditional logic, forming the backbone of a decentralized society (DeSoc).

Practical applications of EAS are vast. It underpins systems for proof-of-humanity and Sybil resistance in governance, verifiable academic and professional credentials, authentic product reviews that cannot be faked, on-chain credit scoring, and attested data oracles. Projects like Gitcoin Passport use EAS to attest to a user's aggregated identity stamps. By providing a universal, minimalist framework for statements of truth, EAS solves the fundamental problem of trust minimization in digital interactions, enabling a new layer of social coordination and verification on the blockchain.

The term attestation originates from the Latin attestari, meaning "to bear witness." In computer science, it refers to a process where a system provides a signed statement about the properties or state of a target, such as in trusted platform modules (TPMs). The Ethereum Attestation Service applies this concept to web3, creating a standardized, schema-based system for any entity—users, DAOs, or smart contracts—to make verifiable claims. It is not a single application but a foundational protocol, akin to a public utility for trust.

The EAS was conceived to solve a fundamental problem in decentralized ecosystems: the lack of a native, generic system for trust and reputation. Prior to its existence, projects built isolated, non-interoperable attestation systems (e.g., for votes, credentials, or reviews). The protocol's origin lies in recognizing the need for a shared, schema registry and a universal attestation graph that any application can query. This allows attestations made for one purpose, like a proof-of-humanity verification, to be reused seamlessly by unrelated applications, such as a governance platform.

Its development was spearheaded by the Ethereum community, with significant contributions from projects like Ethereum Name Service (ENS) and Gitcoin, which became early adopters. The "Service" in its name reflects its design as permissionless and non-custodial infrastructure; it does not store data itself but provides the standards and smart contracts for creating, indexing, and verifying attestations. This origin as a neutral, composable base layer is key to its role in enabling decentralized identity, credit scoring, and onchain reputation systems across the Ethereum ecosystem and beyond.

The attestation lifecycle begins with schema creation. A schema defines the structure of the attestation data, specifying the field names and data types (e.g., string, uint256, address). This schema is registered on-chain, creating a reusable template. For example, a KYCStatus schema might include fields for userAddress, verifiedDate, and providerId. Once a schema exists, any authorized attester—which can be a smart contract, an off-chain service, or an EOA—can create an attestation by referencing the schema's unique identifier (schemaUID) and providing the corresponding data.

The core action is attestation issuance. Using the attest function, the attester submits the structured data, which is permanently recorded on the Ethereum blockchain or a compatible Layer 2. Each attestation receives a unique identifier (attestationUID) and is cryptographically linked to the schema, the attester's address, the subject (the entity being attested about), and a recipient (optional). This creates an immutable, verifiable record. The EAS supports both on-chain and off-chain attestations; off-chain data is stored in a decentralized manner (e.g., IPFS) with only its hash committed on-chain for efficiency.

The final, critical phase is verification and revocation. Any party can trustlessly verify an attestation by querying the EAS contract with the attestationUID to confirm its existence, validity, and data integrity. The attester (or a designated revoker) can optionally revoke an attestation, which marks it as invalid without deleting it, providing a mechanism for correcting errors or updating statuses. This complete lifecycle—schema definition, issuance, and verifiable consumption—enables a portable, composable layer for reputation, credentials, and proofs across the decentralized ecosystem.