Where an NFT's data lives

The image you see when you look at an NFT is almost never on the blockchain. The token holds a link, and the link leads somewhere else. This lesson explains where, and why it decides whether the NFT can change or disappear.

Why not on the blockchain?

Storing data on a blockchain is expensive, because every node keeps a copy for ever. Storing a whole image that way costs a great deal in fees. So most collections store a short link in the contract and keep the rest elsewhere.

The chain of links

The token in the contract holds a link, called the token URI.
That link leads to the metadata: a small text file listing the NFT's name, description, traits and a second link.
The second link leads to the image or other file.

Wallets and marketplaces follow these links and show you the result. The NFT is only as permanent as the weakest link in that chain.

Three places the data can be

An ordinary web server. The link is a normal web address. Whoever controls the server can change the file, or stop paying for hosting. Then the token still exists and points at nothing, or at something different.

IPFS. A file-sharing network where a file's address is worked out from its contents. That address is called a content identifier.

Change one pixel and the identifier changes. So a link of this kind cannot be quietly pointed at different data.
The file stays available only while at least one computer on the network keeps a copy. Keeping a copy is called pinning. If nobody pins it, the file can vanish even though the link is still correct.

On the blockchain itself. A few collections store everything in the contract. This is the most permanent option and the rarest, because of the cost.

Two kinds of IPFS link

An IPFS link can be written in two ways:

As ipfs:// followed by the identifier. This is the proper form. It works as long as anyone on the network has the file.
As a web address that runs through a gateway, a website that fetches IPFS files for ordinary browsers. If that gateway shuts down, the link breaks even though the file still exists.

IPFS's own guidance for NFT creators says gateway links should not be the main link stored in the token.

Can the link itself be changed?

Sometimes. Some contracts let their owner update where tokens point. Projects use this to reveal artwork after a sale, or to fix mistakes. It also means the owner could swap what your token shows.

Some contracts lock the links for good. Marketplaces may label this as frozen metadata.

How to check

On a marketplace or a block explorer, look at the token's details:

Where does the token URI point? A web address, a gateway, or ipfs://.
Is the metadata frozen? Or can the contract's owner change it?
Who is keeping the files available? A project that has gone quiet may stop.

Lesson 34 showed how to read a block explorer.

What a marketplace shows

A marketplace is a window onto the blockchain. It can hide or remove a listing from its own site. The token still exists in the contract and still belongs to you, but it may be hard to sell if the main marketplaces will not display it.