Soulbound Tokens & On-Chain Reputation

What you'll learn

• The 2022 Pitch: A Decentralized Society
• The Technical Standards: EIP-5114 and ERC-5192
• What Actually Shipped: POAP, Galxe, Citizen House
• Why Most of the SBT Pitch Failed
• On-Chain Reputation Today

Key terms

Soulbound Token (SBT)

A token bound to a single wallet ("Soul") and non-transferable by design. Concept introduced in Vitalik Buterin, Glen Weyl, and Puja Ohlhaver's May 2022 paper "Decentralized Society: Finding Web3's Soul".

"Decentralized Society" paper

36-page May 2022 paper by Buterin/Weyl/Ohlhaver proposing SBTs as the missing primitive for non-transferable credentials and reputation in crypto. Sparked widespread industry interest but most proposed use cases never shipped at scale.

ERC-5192

Minimal Soulbound NFT standard. Extends ERC-721 with a single `locked(tokenId)` function that returns true to indicate non-transferability. Simple and widely implementable.

EIP-5114

Soulbound Badge standard. More opinionated than ERC-5192: badges have exactly one owner from mint forever, with no transfer possible. Less adopted because issuers usually need revocation, which the spec does not gracefully permit.

POAP (Proof of Attendance Protocol)

Launched 2019, predating the SBT concept. Issues commemorative NFTs for event attendance — technically transferable but socially treated as bound. Over 8 million POAPs minted across hundreds of thousands of events.

Galxe

Credential and quest platform (formerly Project Galaxy) where users earn on-chain credentials from completing tasks across many crypto applications. Tens of millions of credentials issued; heavily used for airdrop allowlists.

Optimism Citizen House

One chamber of the Optimism Collective's bicameral governance. Voting power derives from non-transferable EAS attestations rather than token holdings. Allocates RetroPGF rounds totaling $300M+ in OP tokens.

RetroPGF (Retroactive Public Goods Funding)

Optimism's funding mechanism distributing OP tokens to public-goods contributors retroactively. Voting done largely by Citizen House. Has distributed $300M+ across multiple rounds.

Sybil resistance

The property of a system to prevent a single actor from gaining outsized influence by creating many fake identities. SBT-style non-transferable credentials and proof-of-personhood systems both aim at this.