> ## Documentation Index
> Fetch the complete documentation index at: https://docs.qedproof.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Anchoring

> How the Merkle log's root is committed on a public chain, so it can't be backdated or silently rewritten.

<Note>
  Anchoring runs on **Base Sepolia**, a testnet, today. Base mainnet anchoring is not switched on yet.
</Note>

An anchor is a public, timestamped commitment to a log root. Its job is to make the log's history provable to
someone who doesn't trust QED Proof's servers at all: once a root is anchored, receipts under it can't be
backdated, quietly edited, or deleted without the tampering being detectable.

## How it works

QED Proof anchors log roots as attestations through the **Ethereum Attestation Service (EAS)** on Base. EAS is a
predeployed public contract with its own schema registry and explorer — QED Proof writes no custom contract for
this. The attestation's data decodes, under QED Proof's published schema, to the log's identifier, the tree size,
and the root hash at that size.

A receipt's `proof.anchor` looks like:

```json theme={null}
"anchor": { "chain": "eip155:84532", "scheme": "eas", "uid": "0x...", "tx_hash": "0x...", "tree_size": 88240 }
```

`chain` is a CAIP-2 chain identifier — `eip155:84532` for Base Sepolia, `eip155:8453` for Base mainnet.

## Checking an anchor

Given a receipt's `proof.anchor` and the issuer's `/.well-known/poaw-keys.json` (which publishes the attester
addresses and schema IDs it considers valid), you can look up the EAS attestation directly on a public Base RPC and
confirm:

* the attestation came from an address the issuer actually publishes as one of its anchor attesters,
* it was made under a schema the issuer publishes,
* and it decodes to the `log_id`, `tree_size`, and `root_hash` the receipt claims (or, if the attested tree is
  larger, that a valid consistency proof connects the two sizes).

The attestation's block timestamp becomes the receipt's proven-by time — the point after which the receipt could not
have been backdated. See [check a receipt](/concepts/check-a-receipt) for running this check yourself with the
reference checker.

## What an anchor gives you, and what it doesn't

An anchor gets a receipt to **trust level 2** (see [trust levels](/concepts/trust-levels)): a checker can confirm
the receipt existed no later than the anchor time, and that it can't be backdated or silently deleted. It does not,
on its own, confirm what a hardware-attested or web-proven verifier build would (trust levels 3 and 4) — those are
specified but not built.