Building a Revealable PFP NFT Contract with ERC-721 and IPFS

Wed, 03 Nov 2021 16:46:16 -0500

A profile-picture NFT contract has one deceptively simple job: connect each token ID to the correct metadata.

The contract in this post does that with a reveal workflow. Before reveal, every minted token returns the same placeholder metadata. After reveal, token 42 returns the metadata assigned to token 42.

before reveal
token 42 -> ipfs://<placeholder-cid>/placeholder.json

after reveal
token 42 -> ipfs://<metadata-cid>/42.json

The useful part is not merely concatenating a number onto a string. We also need to enforce the supply cap, reject nonexistent token IDs, stop minting before disclosure, prove that the final metadata was chosen before deployment, and freeze that metadata after reveal.

Pinning NFT Images and Metadata to IPFS with Pinata

Wed, 03 Nov 2021 16:46:16 -0500

An NFT is not the image.

For a typical ERC-721 token, the smart contract returns a metadata URI. The metadata document at that URI describes the token and points to its image. If either pointer can be changed without limits, the thing a collector sees can change even though the token itself never moved.

That is a trust problem.

In this post, I will use IPFS and Pinata to give the image and metadata layers content-addressed identities. I will also use my Pinata IPFS scripts for NFT projects to pin images independently and pin the finished metadata as a directory.

ERC-721 on Coderrob

Building a Revealable PFP NFT Contract with ERC-721 and IPFS

Pinning NFT Images and Metadata to IPFS with Pinata