Ordinals

Ordinals is a protocol that makes NFT-like assets possible on Bitcoin by numbering individual satoshis — the smallest units of bitcoin — and attaching data to them. Created by developer Casey Rodarmor and launched in early 2023, it assigns each satoshi a serial number based on the order it was mined (its "ordinal"), so a specific satoshi can be tracked as it moves between wallets and treated as a unique collectible.

The data attached to a satoshi is called an inscription: an image, text, or other file embedded directly in a Bitcoin transaction's witness data. For example, a pixel artwork can be inscribed onto satoshi number such-and-such, and whoever controls that satoshi owns the artwork — fully on-chain, with no separate metadata server. Collections of inscribed satoshis trade on marketplaces much like Ethereum NFTs.

A common misconception is that Ordinals required changing Bitcoin's rules; it works within existing consensus rules, using conventions layered on top, which is also why it was controversial — some bitcoiners objected to block space being used for images rather than payments, while others welcomed the new use case and fee revenue for miners. Ordinals also enabled BRC-20, a convention for fungible tokens via text inscriptions, extending the experiment further.