Proof of Existence (Builder)

What is Proof of Existence?

Proof of Existence lets you prove that a specific file (or set of files) existed at a particular point in time. A SHA256 hash of your file is permanently recorded on the Ethereum blockchain. Later, anyone can verify the file by computing its hash and comparing it to the on-chain record.

Step-by-Step Guide

1. 1

   Sign in and connect your wallet

   You need both an AlwaysProof account and a crypto wallet like MetaMask. Sign in to your account, then connect your wallet using the wallet button in the header.

2. 2

   Go to Builder

   Navigate to Create and choose the Wallet option, or go directly to the NFT Builder.

3. 3

   Click ProofSet and choose "Simple"

   Click the ProofSet button to open the choice dialog, then select Simple ProofSet. You can select multiple files at once. Each file is hashed locally in your browser — your files are never uploaded to our servers.

4. 4

   Review the file list and root hash

   The hash of each file is computed locally and a root hash is derived from the full list. You can download or copy the file list for your records. Edit the descriptive name to something meaningful for easy identification later.

5. 5

   Add other items if desired (optional)

   The Builder lets you combine your ProofSet with other item types. You can add messages, binary data, or individual file hashes alongside the ProofSet — all in a single NFT.

6. 6

   Mint your NFT

   Click Mint and your wallet will prompt you to sign the transaction. Once confirmed, your proof is permanently recorded on the Ethereum blockchain. You can view it on your My NFTs page.

How to Verify Later

To verify a file against its blockchain proof, compute the SHA256 hash of the file and compare it to the hash stored on-chain. If the hashes match, the file is identical to what was recorded. Any modification — even a single byte — produces a completely different hash.

For a multi-file ProofSet, download the file list from your My NFTs page. This list contains each filename and its individual SHA256 hash. Recompute the SHA256 of each file with your own tools, then verify each hash matches. The final on-chain hash is the SHA256 of the entire hash list itself, so you can also verify that independently.

Advanced users can also verify a ProofSet from the command line using @alwaysproof/proofset.

Credit Card Alternative

If you don't have a crypto wallet, you can still record file proofs using a credit card. The credit card flow is simpler — no wallet setup required. See the credit card guide for a step-by-step walkthrough.