Proof

One API call stamps any content with a permanent, publicly verifiable provenance record. Works from any language, any agent, any pipeline.

import { stamp, hashText } from "@tatastu/proof"

const hash = await hashText("Hello, world!")
const receipt = await stamp({ contentHash: hash, title: "My post" })
console.log(receipt.verifyUrl)
// → https://proof.tatastu.dev/p/prf_01jz...

Live service: proof.tatastu.dev — verification is always free.

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What it does

A stamp takes the SHA-256 of any content (text, file, JSON, code, binary) and records:

• Who signed it (a creator identity you provide, or anonymous)
• When it was signed (millisecond-precision, bounded by the daily Merkle anchor)
• An Ed25519 signature from the Tatastu Proof service's key-transparency log

Within 24 hours, stamps are batched into an RFC 6962 Merkle tree. The root is anchored to Arweave (permanent storage) and Base (EVM on-chain calldata). After anchoring, you can verify the stamp with zero network calls using the offline verifier in this repo.

What a stamp does not prove: authorship truth. The service records "this signer claimed this content at this time." The claimed time (signedAt) and proven time (anchored) are distinct and both shown on every verify page.

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Install

npm install @tatastu/proof

Or use without installing:

npx tsx examples/eu-ai-act-label.ts

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Quickstart

Stamp text

import { stamp, hashText } from "@tatastu/proof"

const hash = await hashText("The report content goes here.")
const receipt = await stamp({ contentHash: hash, title: "Q3 Report" })
console.log(receipt.verifyUrl)   // https://proof.tatastu.dev/p/prf_...
console.log(receipt.byline)      // "Verified · https://proof.tatastu.dev/p/prf_..."

Stamp a file (Node.js)

import { stamp, hashNodeBuffer } from "@tatastu/proof"
import { readFile } from "node:fs/promises"

const bytes = await readFile("./report.pdf")
const receipt = await stamp({
  contentHash: await hashNodeBuffer(bytes),
  contentType: "application/pdf",
  title: "Q3 Financial Report",
  apiKey: process.env.TATASTU_API_KEY,
})

Verify any content

import { verify, hashText } from "@tatastu/proof"

const { proofs } = await verify(await hashText("The report content goes here."))
if (proofs.length > 0) {
  console.log("Authentic:", proofs[0].verifyUrl)
  console.log("Status:", proofs[0].status)   // SIGNED | ANCHORED | CONFIRMED
}

Stamp a file in the browser (drag-and-drop)

import { stamp, hashBlob } from "@tatastu/proof"

const file = dropEvent.dataTransfer.files[0]
const receipt = await stamp({
  contentHash: await hashBlob(file),
  title: file.name,
})

See examples/browser-drop.html for a complete self-contained verify page with no build step.

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MCP (agent use)

Add proof.tatastu.dev/mcp to your Claude Code, Cursor, or Windsurf config:

{
  "mcpServers": {
    "tatastu-proof": {
      "url": "https://proof.tatastu.dev/mcp"
    }
  }
}

The agent can then call create_proof and verify_proof directly. See examples/agent-mcp.md for the full config and tool reference.

---

EU AI Act compliance

EU AI Act Article 50(4) requires machine-readable provenance on AI-generated content. The deadline is 2 August 2026.

import { stamp, hashText } from "@tatastu/proof"

const aiOutput = "AI-generated text goes here."
const receipt = await stamp({ contentHash: await hashText(aiOutput) })

const labeledOutput = {
  text: aiOutput,
  _proof: {
    contentHash: receipt.contentHash,
    proofId: receipt.proofId,
    verifyUrl: receipt.verifyUrl,
    signedAt: receipt.signedAt,
    bylineHtml: receipt.bylineHtml,
  },
}

Run the full example with no setup:

npx tsx examples/eu-ai-act-label.ts

See docs/eu-ai-act.md for the compliance guide.

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How verification works

Every stamp is:

1. Signed immediately with an Ed25519 key from the service's transparency log
2. Batched daily into an RFC 6962 Merkle tree (0x00/0x01 domain-separated prefixes)
3. Anchored — the Merkle root written to Arweave (permanent) and Base (on-chain calldata)
4. Confirmed once the Arweave transaction has sufficient confirmations

After anchoring you can verify with the public key and inclusion path — no network, no trust, no service required.

Four verified layers on every verify page

1. Ed25519 signature — the service signed the canonical receipt
2. RFC 6962 Merkle inclusion — the stamp is in the anchored batch
3. Arweave anchor — the Merkle root is on Arweave
4. Base calldata — the root is in an EVM transaction on Base

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Offline verification

After a stamp reaches ANCHORED status, you can verify it with no network calls:

import { getBundle, hashNodeBuffer } from "@tatastu/proof"
import { verifyOffline } from "@tatastu/proof/verify/offline"
import { readFile } from "node:fs/promises"

const bytes = await readFile("./report.pdf")
const bundle = await getBundle("prf_01jz...")
const result = await verifyOffline(bundle, await hashNodeBuffer(bytes))
console.log(result.valid, result.signatureVerified, result.merkleVerified)

verify/offline.ts is a single 200-line file with zero dependencies. Copy it into any project. It uses only the Web Crypto API (SubtleCrypto), available in Node 18+, Deno, and modern browsers.

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Pricing

Tier	Price	Stamps	Status
Free	$0	25/month	Live
Tatastu membership	$20/month (the whole Tatastu app)	500/month included	Live
Starter bundle	$8	100 (no expiry)	Launching soon
Creator bundle	$35	500 (no expiry)	Launching soon
Creator subscription	$12/month	500/month	Launching soon
Pay-per-stamp (x402)	$0.10, or $0.05 with API key	n/a	Launching soon

Verification is always free and requires no account.

"Launching soon" tiers are priced and committed but not yet purchasable; the API never routes you to a paywall that doesn't exist. Full, always-current pricing: proof.tatastu.dev/pricing (mirrored in docs/pricing.md).

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Contributing

See CONTRIBUTING.md. The service, Worker, and D1 schema are in a private repo — this repo contains only the public SDK, offline verifier, and examples.