Privi Anchor

Hash anchoring and proof-of-existence on chain for AI agents and apps. Free with an API key.

Hosted MCP Server

npx add-mcp 'https://privi-anchor.onrender.com/mcp'

Installs into Claude Code, Codex, Cursor and more

Documentation

Privi Anchor MCP

Timestamped proof that data existed, on chain. Any AI agent can fingerprint what it produced or relied on (a report, generated image, dataset, contract, model card, audit-log head) and anchor that fingerprint on chain. Anyone can later prove the exact content existed at that time and hasn't changed, by checking the chain itself rather than trusting Privi.

Works with Claude, ChatGPT, Cursor, VS Code and custom agents. Part of the Privi suite with Privi Verify and Privi Ledger.

Live: https://privi-anchor.onrender.com/mcp, anchoring on Base (chain ID 8453) until the Privi chain mainnet launches, then it moves there. Anchors made earlier on the Privi EVM Devnet (chain 262144) stay recorded. anchor_verify reports them as devnet anchors instead of failing them, and you can re-anchor any hash to get a Base receipt.

Tools

Tool	Access	What it does
`anchor_status`	free	Chain, anchor wallet, gas balance, totals
`anchor_hash_text`	free	SHA-256 of text, ready to anchor
`anchor_verify`	free	Proves on chain that a hash was anchored, by whom and when. With a receipt's `tx_hash` + `proof`, uses chain data only
`anchor_hashes`	API key	Anchors 1-100 hashes in one transaction; returns a receipt per hash

Only hashes go on chain, never content.

How it works

The hashes in a call become leaves of a SHA-256 Merkle tree (node = sha256(min(a,b) || max(a,b))).
One zero-value transaction from the anchor wallet to itself carries the root in its data: 0x50525641 ("PRVA") + 0x01 + 32-byte root. No contract is needed.
Each hash gets a receipt: the transaction hash and its Merkle proof.
To verify, read the transaction from any Base RPC node (or basescan.org), take the root from its data, and recompute it from the hash and proof. The block's timestamp is the proof of when.

Independent check in a few lines:

import hashlib
def node(a, b): return hashlib.sha256(min(a, b) + max(a, b)).digest()
x = bytes.fromhex(my_hash)
for sib in proof: x = node(x, bytes.fromhex(sib))
assert x.hex() == tx_input[12:]   # strip "0x" + "50525641" + "01"

Access

anchor_hashes needs Authorization: Bearer <key> with a key from ANCHOR_API_KEYS and is rate-limited per key. It's free with a key. Each call is one Base transaction (a fraction of a cent of gas, paid by the anchor wallet), so the server also enforces a daily budget (ANCHOR_MAX_TX_PER_DAY, default 500). Batch up to 100 hashes per call.

Run, test, deploy

pip install -e ".[dev]"
cp .env.example .env     # set ANCHOR_PRIVATE_KEY and ANCHOR_API_KEYS
pytest
privi-anchor-mcp         # HTTP :8000, MCP at /mcp

The anchor wallet is a hot key. Keep only a little ETH on Base in it for gas (about $5 lasts weeks at the default budget). /status shows its balance and gas_ok.