Crypto glossary
Soulbound token (SBT)
A soulbound token (SBT) is a non-transferable token tied to one wallet, used to represent identity, credentials, memberships or reputation on a blockchain.
The term comes from a 2022 paper by Vitalik Buterin, E. Glen Weyl and Puja Ohlhaver describing a 'decentralized society' built on non-transferable tokens. Technically, an SBT is usually an NFT whose transfer functions are disabled, so it stays in the wallet that received it. Standards such as ERC-5192 signal to wallets and marketplaces that a token is locked, and some versions let the issuer revoke it.
Because it cannot be sold, an SBT can stand for things that should not be bought: attendance at an event, completion of a course, a KYC check, membership of a DAO or a history of on-chain activity. Projects use them as attestation badges, for quest rewards, for Sybil-resistant airdrops and as building blocks of on-chain reputation.
Binding credentials to a single wallet creates problems when keys are lost, so recovery mechanisms are needed. Public, permanent tokens can also reveal sensitive information about a person, and a wallet holding an SBT may still be controlled or sold by someone else.
Example
After completing a security course, a developer receives a soulbound token in their wallet; a hiring DAO checks it as proof of the certification, and the token cannot be transferred to anyone else.