Free, secure, blockchain-based digital timestamping service.
Gridcoin Blockchain Stamp allows anyone to create tamper-proof, publicly verifiable timestamps for documents and digital files — without uploading any data. Powered by the Gridcoin blockchain.
Use the service | Learn more | Tor access
Gridcoin Blockchain Stamp is an open-source document timestamping tool that proves a file existed at a specific point in time. It works by recording a cryptographic hash of your document on the Gridcoin blockchain — creating a permanent, immutable, and publicly verifiable proof of existence.
Your files never leave your device. The SHA-256 hash is computed entirely client-side in your browser. We do not store, upload, or access your documents — only the resulting hash is written to the blockchain.
- Free to use — No account required, no fees. The service is offered at zero cost.
- Permanent proof links — Every stamped document receives a unique, shareable proof URL that serves as lasting evidence of its existence.
- Privacy-first — No tracking pixels, no data collection. The only analytics tool used is Plausible, a privacy-friendly alternative to Google Analytics.
- Open source — Fully transparent codebase under the MIT license.
- Tor accessible — Available as a hidden service for users requiring additional anonymity.
- Blockchain-secured — Proofs are anchored to the Gridcoin blockchain, making them transparent, unalterable, and permanent.
Confirm you created or possessed a document at a specific time — without revealing the document itself. Useful for intellectual property, creative works, and trade secrets.
Establish a verifiable record that a contract, agreement, research paper, or any digital file existed before a certain date. Blockchain Stamp serves as a decentralized alternative to traditional trusted timestamping authorities.
Detect even the smallest modification to a file. If a single bit changes, the hash will differ — allowing you to prove a document has remained unaltered since it was stamped.
Blockchain timestamps can support legal claims by providing an independent, tamper-proof record of when a document was created. The decentralized nature of blockchain makes the proof independent of any single organization.
Researchers can timestamp datasets, manuscripts, and experimental results to establish priority and protect against disputes over originality.
- Drag and drop your file onto stamp.gridcoin.club
- The SHA-256 hash is calculated in your browser — the file never leaves your device
- The hash is recorded on the Gridcoin blockchain in a transaction
- You receive a permanent proof link you can share or store as evidence
- To verify a file later, simply drop it again — if the hash matches an existing stamp, the original timestamp is confirmed
Blockchain Stamp embeds document hashes in the Gridcoin blockchain using the OP_RETURN script opcode, which creates an unspendable transaction output encoding the hash.
Transaction structure:
6a46 5ea1ed 000001 <hash1> <hash2>
| Segment | Meaning |
|---|---|
6a46 |
OP_RETURN script (hex) |
5ea1ed |
Magic bytes — reads as "Sealed" |
000001 |
Protocol version (0.0.1, semver) |
<hash1> |
First SHA-256 hash (32 bytes) |
<hash2> |
Optional second SHA-256 hash |
Each transaction can store up to two hashes, reducing costs and improving efficiency.
Cost per proof: ~0.06 GRC (approximately 0.00000001 GRC burned + ~0.05 GRC transaction fee). All future protocol versions will maintain backward compatibility.
This is a monorepo managed with Nx, containing:
| Package | Description | Stack |
|---|---|---|
packages/frontend |
Web application and UI | Next.js, TypeScript |
packages/backend |
API server, blockchain interaction, stamp processing | TypeScript, Prisma |
- Language: TypeScript
- Frontend: Next.js
- Backend: Node.js with Prisma ORM
- Blockchain: Gridcoin (via gridcoin-rpc)
- CI/CD: CircleCI with semantic-release
- Containerization: Docker
- Node.js 22+ (see
.nvmrc) - Docker (for local development)
- Access to a Gridcoin wallet node
git clone https://github.com/gridcoin-community/stamp.gridcoin.club.git
cd stamp.gridcoin.club
npm installStart development environment
docker-compose upnpm test| Feature | Geidcoin Blockchain Stamp | Traditional TSA | Other Blockchain Services |
|---|---|---|---|
| Cost | Free | Paid | Varies |
| Account required | No | Yes | Often |
| File uploaded to server | No | Yes | Sometimes |
| Proof publicly verifiable | Yes | No | Varies |
| Open source | Yes | No | Rarely |
| Blockchain anchored | Yes (Gridcoin) | No | Yes (various chains) |
| Tor accessible | Yes | No | Rarely |
Contributions are welcome. This project uses:
- Commitizen for conventional commits
- semantic-release for automated versioning
- CircleCI for continuous integration
Please open an issue before submitting a pull request for significant changes.
- Live service: stamp.gridcoin.club
- Tor hidden service: u4embjw2uzwpdubgm72ywbmixte4kqgwurc4r4rp6elhlokutdfsy4id.onion
- Gridcoin: gridcoin.us
- Gridcoin RPC client: gridcoin-rpc
MIT