> For the complete documentation index, see [llms.txt](https://docs.seismic.systems/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.seismic.systems/clients/python/api-reference/transaction-types/legacy-fields.md).

# LegacyFields

Standard EVM transaction fields used in [`TxSeismicMetadata`](/clients/python/api-reference/transaction-types/tx-seismic-metadata.md) for AAD (Additional Authenticated Data) construction.

## Definition

```python
@dataclass(frozen=True)
class LegacyFields:
    chain_id: int
    nonce: int
    to: ChecksumAddress | None
    value: int
```

## Fields

| Field      | Type                      | Description                                         |
| ---------- | ------------------------- | --------------------------------------------------- |
| `chain_id` | `int`                     | Numeric chain identifier (e.g., `5124` for testnet) |
| `nonce`    | `int`                     | Sender's transaction count                          |
| `to`       | `ChecksumAddress \| None` | Recipient address, or `None` for contract creation  |
| `value`    | `int`                     | Amount of wei to transfer                           |

## Example

```python
from seismic_web3 import LegacyFields

legacy = LegacyFields(
    chain_id=5124,
    nonce=42,
    to="0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266",
    value=1 * 10**18,  # 1 ETH in wei
)
```

## Notes

* Called "legacy" because these fields are unchanged from standard Ethereum transactions — present in every tx type since pre-EIP-2718
* Does not include `gas`, `gasPrice`, or `data`. These are the standard EVM fields that go into the AAD — `gas`/`gasPrice` are excluded because they aren't part of the authenticated context, and `data` is the plaintext being encrypted (so it can't also be AAD input)
* The AAD also includes [`SeismicElements`](/clients/python/api-reference/transaction-types/seismic-elements.md) (encryption params, block hash, expiry). The node validates these fields before the transaction enters the mempool

## See Also

* [TxSeismicMetadata](/clients/python/api-reference/transaction-types/tx-seismic-metadata.md) — uses LegacyFields
* [SeismicElements](/clients/python/api-reference/transaction-types/seismic-elements.md) — Seismic-specific fields (contrast)
* [UnsignedSeismicTx](/clients/python/api-reference/transaction-types/unsigned-seismic-tx.md) — full transaction structure


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