Proof of Existence on Cardano — and the open standard behind it.
Hash any content, anchor the digest on the Cardano blockchain, and later prove that this content existed on or before a given block time — without trusting our servers, our domain, or any issuer identity.
We authored and maintain Label 309, the open standard for this, and publish its complete reference implementation as open source. The standard is issuer-agnostic and standalone-verifiable: any wallet can publish a proof, and anyone can verify it from just the transaction and a public block explorer — no issuer server required, ever.
Licensed Apache-2.0 (code) and CC-BY-4.0 (the specification).
| Project | Package | What it is |
|---|---|---|
| label-309 | — | The standard: spec, CDDL, JSON Schemas, registries, conformance vectors |
| label-309-ts | @cardanowall/sdk-ts · npm |
TypeScript reference — primitives, wire format, SDK + standalone verifier |
| label-309-py | cardanowall-sdk · PyPI |
Python SDK — byte-parity twin |
| label-309-rs | cardanowall · crates.io |
Rust SDK — byte-parity twin |
| label-309-cli | cardanowall-cli · crates.io |
Standalone CLI verifier + toolkit |
All three language SDKs are validated against the same canonical conformance vectors and produce byte-identical output.
- 📖 The standard: label309.org
- 🌐 Hosted service: cardanowall.com
- 📨 Contact: hello@cardanowall.com