Technical Definition

Soulbound Token (SBT)

A soulbound token (SBT) is a non-transferable token tied permanently to a single wallet ("soul"). Unlike a normal NFT or ERC-20, an SBT cannot be sold or sent to another address — it represents an identity-linked credential, achievement, or membership.

By Crypto University Editorial
Proof of PersonhoodERC-6551NFT

✦ Key Insight

SBTs are the building block for on-chain reputation, credentials, and identity. For traders, they matter both as a primitive (some airdrops, governance rights, and access tiers depend on SBTs) and as a regulatory signal (some compliance-friendly tokens use SBT-like restrictions).

✕ Common Misconceptions

Treating SBTs as transferable assets — they are not.

Assuming "soulbound" implies "private"; SBTs are on-chain and publicly readable.

Designing systems that depend on SBTs without a revocation or rotation path.

Detailed Explanation

How It Works: An SBT is typically implemented as a customized NFT whose transfer function reverts unconditionally. Issuance is controlled by an authorized entity — a DAO, a credentialing organization, an on-chain verifier — and the token sits in the recipient's wallet as proof of the claim.

FAQs:

  • Can SBTs be revoked? If designed to be — many include a revoke function controlled by the issuer.

  • What if I lose the wallet holding my SBTs? They are typically not portable to a new wallet without re-issuance.

In Practice

“A DAO issues an SBT to every member who has voted on at least ten proposals over a year. The SBT cannot be sold and is used to gate access to a private signaling channel.”

Dig Deeper

NFT

An NFT (non-fungible token) is a unique cryptographic token on a blockchain that represents ownership of a specific digital or physical asset and cannot be exchanged on a one-to-one basis like fungible cryptocurrencies.

ERC-6551

ERC-6551 (Token-Bound Account) ERC-6551 is an Ethereum standard that gives every ERC-721 NFT its own smart contract wallet. The NFT becomes the owner of an account that can hold tokens, sign transactions, and interact with dApps — making the NFT itself a portable, on-chain identity and asset container.

Proof of Personhood

Proof of personhood (PoP) is a system that verifies an account corresponds to a unique human being, without necessarily revealing that human's identity. It is the cryptographic answer to "how do you ensure one person, one account?"