xProof — Blockchain Proof of Existence for Agents

xProof anchors agent outputs to the MultiversX blockchain. Any text, hash, file, or decision becomes a permanent, tamper-proof record with a verifiable on-chain certificate.

Use this skill when:

• Certifying agent outputs, decisions, or reports that need to be verifiable
• Anchoring content before it is shared, published, or acted upon
• Building audit trails for autonomous agent pipelines
• Proving a document or output existed at a specific point in time

Authentication

Option 1 — API Key (recommended): Set XPROOF_API_KEY in your environment. Get a key at https://xproof.app.

Option 2 — x402 (no account required): Send USDC on Base. The API returns a 402 with payment instructions; include the X-Payment header (base64-encoded JSON) in your follow-up request.

Certify Text or a Hash

# Certify text content
curl -s -X POST https://xproof.app/api/proof \
  -H "Authorization: Bearer $XPROOF_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "content": "The agent decided: deploy to production at 2026-02-20T14:00:00Z",
    "metadata": {"agent": "deploy-bot", "pipeline": "release-v2.1"}
  }'

# Certify a SHA-256 hash (if you already have it)
curl -s -X POST https://xproof.app/api/proof \
  -H "Authorization: Bearer $XPROOF_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"hash": "sha256:<64-char-hex>"}'

Response:

{
  "id": "cert_abc123",
  "status": "pending",
  "hash": "sha256:...",
  "txHash": "...",
  "blockchainUrl": "https://explorer.multiversx.com/transactions/...",
  "verifyUrl": "https://xproof.app/verify/cert_abc123",
  "certifiedAt": "2026-02-20T14:00:05Z"
}

Certify a File

# Hash a file locally and certify the hash
FILE_HASH=$(sha256sum report.pdf | awk '{print $1}')

curl -s -X POST https://xproof.app/api/proof \
  -H "Authorization: Bearer $XPROOF_API_KEY" \
  -H "Content-Type: application/json" \
  -d "{\"hash\": \"sha256:${FILE_HASH}\", \"metadata\": {\"filename\": \"report.pdf\"}}"

Batch Certify (up to 50)

curl -s -X POST https://xproof.app/api/batch \
  -H "Authorization: Bearer $XPROOF_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "proofs": [
      {"content": "Output 1"},
      {"content": "Output 2"},
      {"hash": "sha256:<hash-3>"}
    ]
  }'

Verify a Certificate

# By certificate ID
curl -s https://xproof.app/api/proof/cert_abc123

# Response includes on-chain status: pending | confirmed | failed

MX-8004 Integration (MultiversX Agent Validation Loop)

xProof implements the full MX-8004 validation loop. To submit a certified proof as an on-chain MX-8004 validation:

# Step 1: Certify the output
CERT=$(curl -s -X POST https://xproof.app/api/proof \
  -H "Authorization: Bearer $XPROOF_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"content": "Agent output to validate"}')