0xcert is an open source permissionless protocol for non-fungible tokens on the blockchain. These tokens are stored in cryptographic wallets and are owned by users. In addition to common functions for transferring and managing standard non-fungible tokens, the 0xcert protocol provides another layer of conventions for creating certified non-fungible tokens for unique assets. These tokens are called Xcerts and are created through a custom minting process. Xcerts represent opinionated non-fungible tokens, which also hold an imprint of an asset. With 0xcert protocol, we can validate a proof of existence, authenticity and ownership of these digital assets without third-party involvement.