# Base L2 Testnet Anchor Walkthrough

> Anchor an Attestix artefact hash to Base L2 testnet via the Ethereum Attestation Service. End-to-end guide with Sepolia faucets, gas estimates, and verification.

This guide walks through anchoring an Attestix identity or credential to Base L2 testnet (Sepolia). Mainnet schema registration is planned for a future release; testnet is the default target today.

## Why anchor?

An Attestix artefact (identity, credential, audit batch) is already Ed25519-signed and hash-chained. Anchoring commits the hash to a public ledger so any third party can:

- Confirm the artefact existed at a specific block height.
- Detect silent mutation of the local store.
- Link an Attestix issuer DID to an on-chain provenance record.

Anchoring is optional. Attestix works fully offline without it.

## Prerequisites

```bash
# v0.4.0-rc.2 release candidate (canonical attestix.* namespace):
pip install --pre attestix

# Stable 0.3.0 still works (legacy flat layout, deprecation shims):
pip install attestix
```

You will need:

1. A Base Sepolia RPC endpoint.
2. A funded wallet on Base Sepolia (0.001 ETH is plenty, free from public faucets).
3. The EAS schema UID for Attestix. This ships with the package.

## Step 1 / Configure the testnet RPC

```bash
export BASE_RPC_URL=https://sepolia.base.org
export EVM_PRIVATE_KEY=0xyour_private_key_hex_here
```

Or via `.env`:

```
BASE_RPC_URL=https://sepolia.base.org
EVM_PRIVATE_KEY=0x0000000000000000000000000000000000000000000000000000000000000000
```

`EVM_PRIVATE_KEY` is the full hex private key with the `0x` prefix. **Treat it as a secret. Never commit it. Never share it.** Use a dedicated test wallet for testnet work; do not reuse mainnet keys.

## Step 2 / Fund the wallet

Use any Base Sepolia faucet. Recommended:

- Coinbase Developer Platform faucet for Base Sepolia: https://portal.cdp.coinbase.com/products/faucet
- Alchemy Base Sepolia faucet: https://www.alchemy.com/faucets/base-sepolia

Send around 0.001 ETH to the address derived from `EVM_PRIVATE_KEY`.

Check balance via the Attestix CLI:

```bash
attestix blockchain balance
```

Or programmatically in Python:

```python
from attestix.services.blockchain_service import BlockchainService

svc = BlockchainService()
print(svc.balance())  # e.g. 0.0012 ETH on Base Sepolia
```

## Step 3 / Estimate cost

```python
svc.estimate_anchor_cost(artifact_id="attestix:f9bdb7a94ccb40f1")
```

Typical numbers on Base Sepolia:

| Field | Value |
|-------|-------|
| Gas | ~48,000 |
| Gas price | ~1 gwei |
| Total | under $0.01 (testnet ETH has no market value) |

## Step 4 / Anchor an identity

```python
tx_hash = svc.anchor_identity(agent_id="attestix:f9bdb7a94ccb40f1")
print(tx_hash)  # -> 0x8f2e4c9b...
```

## Step 5 / Anchor a credential

```python
tx_hash = svc.anchor_credential(credential_id="urn:uuid:9e2f7a3c-...")
```

## Step 6 / Anchor a batch

Merkle-batch 100 artefacts into a single on-chain write:

```python
tx_hash = svc.anchor_audit_batch(
    artifact_ids=[...],  # up to 10,000 per batch
)
```

Gas cost stays ~48k regardless of batch size. The proof size grows as `O(log n)` per artefact.

## Step 7 / Verify an anchor

```python
status = svc.verify_anchor(artifact_id="attestix:f9bdb7a94ccb40f1")
# -> { "confirmed": True, "block": 23047881, "tx": "0x8f2e...", "schema": "AttestixAgentIdentityV1" }
```

Run this on a different machine to prove the local store has not been tampered with.

## Step 8 / Inspect on a block explorer

Paste the tx hash into Base Sepolia block explorer. You will see:

- The EAS attestation call
- The Attestix schema reference
- The artefact hash as a bytes32 field

Anyone can run the same verification without contacting Attestix or VibeTensor.

## Troubleshooting

### `Error: BASE_RPC_URL not set`

See [configuration](/docs/reference/configuration) for all environment variables.

### `Error: insufficient funds`

Top up the wallet at a Base Sepolia faucet.

### `Error: schema UID mismatch`

Upgrade to the latest Attestix package: `pip install --upgrade attestix`.

## Mainnet status

Mainnet schema registration is on the [roadmap](/docs/project/roadmap). Once the mainnet schema is registered and validated, `BASE_RPC_URL` can be pointed at `https://mainnet.base.org` and the same flow applies with real gas cost. Until then, use testnet.