Learn

ERC-721 (RFC)

ERC-721 is the basic NFT. Each token has its own number and one current owner. A dollar can be swapped for any other dollar. An ERC-721 token cannot. Token 5 and token 6 are different items, even when they live in the same collection.

The spec is Final. The rules for ownership and transfer are stable. A project can still add its own extra rules on top.

How the token works

Think of a coat check. You get a numbered ticket. The desk can look up that number and see who holds the ticket. The coat is not inside the ticket. The ticket is the claim. ERC-721 is that ticket, written on a public chain so anyone can check it.

1. The collection. A smart contract is the rulebook. It can issue many tokens. Each one gets a number, the tokenId. The contract can also have a name and a short symbol, like a club name and its initials.
2. The owner. ownerOf(tokenId) answers which wallet holds that number. balanceOf answers how many tokens from this collection a wallet holds. One token still has only one owner at a time.
3. The transfer. The owner can send the token to another wallet. safeTransferFrom is the careful version. It checks that the receiver can accept an NFT, so the token is not sent to a contract that will trap it. A normal transfer still needs a network fee.
4. Permission to move it. approve lets one address move one token.setApprovalForAll lets a shop move any of your tokens in that collection. That is how a marketplace lists an item without you sending the token first. You can turn that permission off. Leave it on only for a shop you trust.
5. The picture or file. This part is optional. tokenURI points to a description, often a small file with a name, a sentence, and an image link. The picture usually sits on a website or a file network. The token is the ownership record, not the file itself. If the link breaks, the token can still exist with a missing picture.
6. The public log. Every transfer and every approval is written as an event. Apps and shops watch that log to show the history. They do not need the project’s private database to see who owns the token now.

What the token does not do

Owning the token means you can transfer that token. It does not, by itself, mean you own the copyright, the company, the server, or the original file on someone’s computer.

• It does not run software or answer questions.
• It does not prove the art is original.
• It does not give the token its own wallet. That is a different standard.
• It does not register an agent identity. That is ERC-8004.
• A broken image link does not delete the token. It only means the description file is gone.

Professional use

A person can use a unique token when one record should have one holder.

• A course certificate or a license that should not be copied as “the same” item.
• A portfolio piece you can show as yours, then transfer to a client if the deal says so.
• A membership pass for a professional group. The door checks the token, not a private list.

The useful part is the public owner check. A client can see that your wallet holds certificate number 42. Selling or sending the token is a separate choice from selling your copyright, unless a written deal says they move together.

Business use

A company can issue tokens when each item, seat, or claim must stay distinct.

• Numbered tickets. Token 100 is one seat, not a coupon anyone can photocopy.
• A product certificate for a physical item, with the token number tied to a serial number.
• A brand character or access pass the company creates, then sells or grants. Shops already know how to list an ERC-721 token.
• A claim or voucher that one department holds and can transfer to another wallet when the owner of that job changes.

The company still has to say, in plain language, what the token includes. The chain records the owner. It does not enforce a refund policy, a warranty, or a job.

Personal use

A person can use the same token for something they simply want to hold or give away.

• Art, music, or a photo, when you want a public record of who holds that edition.
• A game item or a pet picture you can trade with someone else.
• A souvenir ticket from an event you want to keep or send to a friend.

You pay a network fee to create or send the token. The file on your laptop does not move unless you also share it. If the image is only a link, the next owner can see it only while that link still works.

Back to Ethereum ERC Standards