What Is an NFT?

2021: The year everything became an “NFT”

The early years of public blockchains produced experiments in almost every direction: currencies, name registries, games, voting, crowdfunding, exchanges, digital collectibles and more.

In 2021 the market decided it especially liked one of those early experiments: non-fungible tokens.

Once NFTs were valuable, people tried to attach the label to almost everything with a blockchain history, and it got absurd. Individual Bitcoin satoshis, the smallest and supposedly interchangeable unit of bitcoin, were numbered, collected one by one, and inscribed with content that is “more commonly known as NFTs.”¹ Terra Nullius, a 2015 Ethereum guestbook contract with no tradable tokens whatsoever, was promoted as Ethereum's first NFT, and Guinness World Records still says so as of October 2026.² The list goes on.

So it is worth cutting through the noise: what exactly is an NFT?

Fungible and non-fungible

Fungible means interchangeable. Any one bitcoin, or any one dollar, is as good as any other, so nobody cares which one they receive. Non-fungible means the opposite: a token that can be told apart from the others in its set and is not freely swappable for them.

That is the literal meaning. In practice the market applies the label more loosely.

Definition 1: the technical definition

An NFT is any unique, ownable, safely tradable asset on a blockchain.

This definition correctly includes much of what people mean by an NFT today, such as CryptoPunks. But it misses in both directions.

It includes things that are NFTs only in this technical sense. Liquidity positions opened through Uniswap v3's position manager are issued as ERC-721 tokens, but each one is a financial position, not a collectible.³ A smart contract whose ownership can be reassigned is unique, ownable and transferable. So is a Namecoin or ENS name registration, which makes an ENS name an NFT in the technical sense, though not in the collectible sense below.

It excludes things the market does consider NFTs. Each of the 30 Curio Cards (2017) is an ERC-20 token issued in many identical copies, so no single token is unique, yet Curio Cards are widely accepted as NFTs: a complete set sold at Christie's in October 2021.⁴

Definition 2: the collectible definition (2021 onward)

An NFT is any blockchain-defined, persistent, tradable token that is part of an author-defined collectible set.

Fail any one of the hard requirements below and a token is not an NFT in this sense. Each soft requirement has accepted exceptions.

Hard requirements

1. Defined and enforced by a real blockchain. The tokens, and the set they belong to, must be known to, defined by and enforced by the rules of a real blockchain, not merely recorded on one.
   Counterexample Counterparty tokens are not on a real blockchain. Counterparty is not a blockchain at all; it is a protocol implemented in software. It writes its messages into Bitcoin transactions as obfuscated bytes (ARC4-encrypted, keyed to each transaction's first input), and Bitcoin neither reads them nor enforces them: to Bitcoin they are opaque data. The obfuscation hides nothing from anyone who looks, since its key is public; it only keeps the data from being recognized at a glance. What those bytes mean is, in Counterparty's own words, “described in the source code.” Miners will confirm a Counterparty transfer that Counterparty itself rejects as invalid.⁵ As the Ethereum whitepaper puts it, such meta-protocols “cannot force the blockchain not to include transactions that are not valid within the context of their own protocols.”⁶

   Compare client diversity. Ethereum runs on many independent client implementations, and that is considered a strength: a client that computes a different state rejects the blocks everyone else accepts, and only it falls off the chain. A second Counterparty implementation that read the same Bitcoin bytes differently would derive a different ledger from the very same blocks, and Bitcoin could not settle which one is right. And Counterparty changes its rules the way any software project does: a file in its GitHub repository lists every rule change, 134 as of October 2026, with the Bitcoin block at which each one takes effect. One change in September 2026 gave node operators “about two hours” to upgrade before it applied.⁷ The only arbiter of who owns a Counterparty token is Counterparty's own software, which makes Counterparty centralized.

2. Deterministic ownership. No expiration, safe tradability, and no backdoors: once a token is yours, it stays yours until you transfer it, and nobody else can take it or rewrite it.
   Counterexamples

   Namecoin names expire. A name that is not renewed or updated within 36,000 blocks (about 250 days) expires, and anyone can then register it. Every renewal re-records the name in a new transaction, and the holder may change what it says. The most famous casualty is Quantum.⁸

   Etherization (2016) records city ownership in a contract whose deployer can, at any time, appoint an address that is allowed to rewrite any city's owner or any player's balance. No function exists to give up that power.⁹

   Counterparty fails here too. It can escrow its own tokens but not bitcoin, so a buyer paying in bitcoin pays first and trusts the protocol to deliver. In a “dispenser” sale, a buyer who is front-run, or who finds the dispenser empty, simply loses the bitcoin: as a Counterparty co-founder wrote in 2024, “It's trivial for the seller to front-run the buyer and get free BTC.” Until mid-2026, a flaw also let anyone take the asset in a pending bitcoin trade on its exchange by paying the bitcoin to themselves. Atomic swaps arrived only in late 2024, and as of October 2026 dispensers remain the usual way to sell.¹⁰

3. Part of a set whose membership is author-defined and blockchain-enforced.
   Counterexamples

   OLGA, a Counterparty asset issued in June 2014 as a single indivisible unit, was issued on its own, not as part of any set.¹¹ A token by itself is neither fungible nor non-fungible, just as a person in a vacuum is neither tall nor short. Fungibility is a comparison property.

   ENS “collections” such as the 999 Club (000.eth through 999.eth) are collector conventions. No contract defines them; membership is decided socially. The names in them also expire unless they are renewed.¹²

Soft requirements

1. Uniqueness.
   Accepted exception The market has accepted semi-fungible tokens (identical copies of each item, interchangeable with one another but not with the set's other items) as bona fide NFTs, as Curio Cards show.⁴
2. Limited supply.
   Accepted exception CryptoKitties (2017). At most 50,000 generation-0 cats could ever be created, but breeding keeps producing new ones, so the collection has no fixed size: more than two million kitties exist, and the contract's only ceiling is a technical one of about 4.3 billion. Everyone considers CryptoKitties an NFT project, and Dieter Shirley of the CryptoKitties team co-authored the ERC-721 NFT standard.¹³ This is why the third hard requirement asks for an author-defined set rather than a finite one: CryptoKitties' set is defined by its contract, even though it keeps growing.
3. Fully on-chain. On-chainness is a spectrum.
   Examples along the spectrum

   CryptoPunks (2017). The original contracts record the punks' artwork only as a SHA-256 hash of one composite image of all 10,000 punks. In August 2021 the full images and attributes were put on-chain in a separate contract, which the original contracts, immutable since 2017, never reference.¹⁴

   Etheria (2015) sits high on the spectrum. Tile ownership, elevations and the voxel sculptures owners build on their tiles are all stored on-chain, so the shape of the entire world can be rebuilt from chain data alone. Only the presentation is off-chain: client software derives each tile's terrain type (water, ice, mountain and so on) from its on-chain elevation and latitude, and draws it with JPEG textures that are not stored on-chain.¹⁵

   Autoglyphs (2019) go further still: the contract generates each artwork on-chain and returns it as text: a 64-by-64 grid of characters. But nothing on-chain says which font to display it in, and the rules for turning each character into a pen drawing exist only as comments in the published source code, which are not stored on the blockchain.¹⁶

   Full on-chainness is therefore difficult, if not impossible.

Two famous “first NFTs” that are not NFTs

Terra Nullius (2015): a guestbook

The Terra Nullius contract, deployed on 7 August 2015, is the source of truth, and it is short. Its one action, claim(message), appends the caller's address, a message and the current block number to a list. There are no tokens, no ownership of anything, and no function that can transfer an entry. Between August 2015 and May 2016, 22 entries were written, such as the very first: “Peter was here.”²

Guinness World Records nonetheless lists Terra Nullius as the “First Ethereum NFT,” and says its contract “logged the ownership of a set of 4,000 blocks in the Ethereum blockchain.”¹⁷ Guinness is wrong. The 2015 contract logs messages, not ownership, and has no limit of 4,000 (it held 4,664 entries as of October 2026). The number 4,000 belongs to a different contract written six years later.

That contract is an ERC-721 wrapper deployed on 27 September 2021, capped at 4,000 tokens, and it arrived together with the claim that Terra Nullius was “the oldest NFT on Ethereum.”² All 4,000 of its tokens have been minted. Only 22 of them wrap the 2015–2016 entries. The other 3,978 are new entries written into the 2015 contract from September 2021 onward; the wrapper's own mint function creates such entries, recording them under the wrapper's address as the claimant. In other words, more than 99% of the “oldest NFT on Ethereum” was minted in 2021.

A token contract written in 2021 does not reach back and turn a 2015 guestbook into an NFT. The guestbook fails both definitions at the most basic level.

Quantum (2014): a Namecoin entry that expired

In May 2014 the artist Kevin McCoy registered a Namecoin name whose value is a short statement in English: it asserts title to a GIF hosted on his own web server, gives that file's SHA-256 hash, links to a tweet, and declares that “title transfers to whoever controls this blockchain entry.”¹⁸ It is often called the first NFT. It fails on every front.

1. It was built to expire, like every Namecoin name.⁸
2. It did expire. The 2014 entry was never renewed and lapsed within a year. On 5 April 2021 a company called Free Holdings registered the same name.¹⁸
3. It was malleable. Its holder can change what it says, and Free Holdings did: in June 2021 it replaced the text the 2014 entry had held.¹⁸
4. The “Quantum” that sold was a 2021 Ethereum token. McCoy minted it as a new ERC-721 token on 28 May 2021, and it sold at Sotheby's that June for $1,472,000. The lot itself calls the Namecoin entry the original, “preserved on a token minted on May 28, 2021.”¹⁸
5. Nothing about it was defined or enforced by the chain, and no set was possible. Namecoin enforces only who controls a name: to its consensus rules, “names and their values are arbitrary binary blobs,” and it “isn't aware of namespaces.” The link between the entry and the artwork is a sentence for humans to read. Monegraph, the art-registration idea McCoy presented with Anil Dash the next day, was a convention and a prototype website layered on Namecoin, not something the chain enforced. And since Namecoin cannot define a collection, Quantum fails the set requirement too.⁸

Sources

1. Ordinals handbook: Inscriptions (“digital artifacts, more commonly known as NFTs”) and Introduction (“Ordinal theory imbues satoshis with numismatic value”).
2. Terra Nullius contract, deployed 7 Aug 2015: 0x6e38A457C722C6011B2dfa06d49240e797844d66. 2021 “oldest NFT” coverage: The Crypto Times, 29 Sep 2021. ERC-721 wrapper, first used 27 Sep 2021, max = 4000: 0x3a921bf2c96cb60d49aff09110a9f836c295713a. Entry counts, entry dates and wrap status read directly from both contracts (number_of_claims, claims, totalSupply, ownerOf) on 16 Oct 2026.
3. Uniswap v3 NonfungiblePositionManager (“Uniswap V3 Positions NFT-V1”): 0xC36442b4a4522E871399CD717aBDD847Ab11FE88.
4. Curio Cards documentation; Curio Cards (Wikipedia), including the Christie's sale of 1 Oct 2021.
5. Counterparty protocol specification (“All of the data is obfuscated by ARC4 encryption”; message formats are “described in the source code”).
6. Ethereum whitepaper, section on alternative blockchain applications and meta-protocols.
7. Counterparty Core, protocol_changes.json (134 entries as of 16 Oct 2026; the require_reveal_source_signature entry sets its activation “about two hours after the v11.5.0 release, so operators have a window to upgrade”).
8. Namecoin FAQ: names semi-expire after 31,968 blocks and expire after a further 4,032; “Expired names can be re-registered by anyone”; “names and their values are arbitrary binary blobs”; Namecoin “isn't aware of namespaces.”
9. Etherization contract, deployed 16 Sep 2016: 0xb40d0312bac389ae0a05053020aac80c9237358b (setUtils, callable only by the deployer, and setOwner, callable by the address it names).
10. Counterparty trade safety: the dispenser rules in the protocol specification and CIP 21; co-founder Adam Krellenstein in counterparty-core issue #1331 (16 Jan 2024); the BTCPay destination fix, commit 53a528b, active from block 952,800 (check_btcpay_destination in the rule-change file above); UTXO support and atomic swaps; event totals from Counterparty's API (209,188 dispenses against 3,683 UTXO attaches, 16 Oct 2026).
11. OLGA asset record: xchain.io/asset/OLGA.
12. ENS: grace period and expiry; ENS forum on the 10k Club (club membership is a filter collectors apply, not a contract property).
13. CryptoKitties core contract, deployed 23 Nov 2017: 0x06012c8cf97BEaD5deAe237070F9587f8E7A266d (PROMO_CREATION_LIMIT 5,000; GEN0_CREATION_LIMIT 45,000). EIP-721.
14. CryptoPunks contracts, each with the same imageHash (ac39af4793119ee46bbff351d8cb6b5f23da60222126add4268e261199a2921b): original, June 2017 and current, June 2017; Larva Labs repository. On-chain images and attributes, deployed 18 Aug 2021: 0x16F5A35647D6F03D5D3da7b35409D65ba03aF3B2.
15. Etheria: FAQ and the world explorer.
16. Autoglyphs contract, deployed 5 Apr 2019: 0xd4e4078ca3495DE5B1d4dB434BEbc5a986197782.
17. Guinness World Records, “First Ethereum NFT”, as published on 16 Oct 2026.
18. Quantum: Rhea Myers, “Regarding Quantum”; the 2014 Namecoin entry as archived from namebrow.se; Sotheby's lot page (“Lot sold: 1,472,000 USD”); the re-registration and later value changes are recorded in Free Holdings v. McCoy, S.D.N.Y., 17 Mar 2023. Monegraph: Cointelegraph, May 2014; Le Random interview with Kevin McCoy, 2024.