> 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/eip712/build-seismic-typed-data.md).

# build\_seismic\_typed\_data

Build a JSON-serializable [EIP-712](https://eips.ethereum.org/EIPS/eip-712) typed-data payload for a Seismic transaction.

This function exists primarily for parity with the TypeScript client, where `eth_signTypedData_v4` is used by browser wallets like MetaMask. In Python you'll typically sign transactions directly with [`sign_seismic_tx_eip712`](/clients/python/api-reference/eip712/sign-seismic-tx-eip712.md), but this function is available when you need the raw typed-data structure (e.g. sending it to a frontend for wallet signing).

## Signature

```python
def build_seismic_typed_data(tx: UnsignedSeismicTx) -> dict[str, Any]
```

## Parameters

| Parameter | Type                                                                                          | Required | Description                      |
| --------- | --------------------------------------------------------------------------------------------- | -------- | -------------------------------- |
| `tx`      | [`UnsignedSeismicTx`](/clients/python/api-reference/transaction-types/unsigned-seismic-tx.md) | Yes      | The unsigned Seismic transaction |

## Returns

| Type             | Description                                                |
| ---------------- | ---------------------------------------------------------- |
| `dict[str, Any]` | Dict with keys `types`, `primaryType`, `domain`, `message` |

## Output structure

The returned dictionary follows the `eth_signTypedData_v4` format:

```json
{
  "types": {
    "EIP712Domain": [
      { "name": "name",              "type": "string"  },
      { "name": "version",           "type": "string"  },
      { "name": "chainId",           "type": "uint256" },
      { "name": "verifyingContract", "type": "address" }
    ],
    "TxSeismic": [
      { "name": "chainId",          "type": "uint64"   },
      { "name": "nonce",            "type": "uint64"   },
      { "name": "gasPrice",         "type": "uint128"  },
      { "name": "gasLimit",         "type": "uint64"   },
      { "name": "to",               "type": "address"  },
      { "name": "value",            "type": "uint256"  },
      { "name": "input",            "type": "bytes"    },
      { "name": "encryptionPubkey", "type": "bytes"    },
      { "name": "encryptionNonce",  "type": "uint96"   },
      { "name": "messageVersion",   "type": "uint8"    },
      { "name": "recentBlockHash",  "type": "bytes32"  },
      { "name": "expiresAtBlock",   "type": "uint64"   },
      { "name": "signedRead",       "type": "bool"     }
    ]
  },
  "primaryType": "TxSeismic",
  "domain": {
    "name": "Seismic Transaction",
    "version": "2",
    "chainId": 1946,
    "verifyingContract": "0x0000000000000000000000000000000000000000"
  },
  "message": {
    "chainId": 1946,
    "nonce": 42,
    "gasPrice": 20000000000,
    "gasLimit": 100000,
    "to": "0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266",
    "value": 1000000000000000000,
    "input": "0xabcd...",
    "encryptionPubkey": "0x02...",
    "encryptionNonce": 12345,
    "messageVersion": 2,
    "recentBlockHash": "0x1234...",
    "expiresAtBlock": 12345678,
    "signedRead": false
  }
}
```

## Field encoding

### `message` values

* **Numeric fields** — integers (not hex strings)
* **Address fields** — checksummed `0x`-prefixed hex strings
* **Bytes fields** (`input`, `encryptionPubkey`, `recentBlockHash`) — `0x`-prefixed hex strings
* **`encryptionNonce`** — the 12-byte nonce converted to an integer via `int.from_bytes(…, "big")`
* **`to`** — becomes the zero address when `tx.to is None`

### `domain`

* **name** — `"Seismic Transaction"`
* **version** — `"2"` (matches `message_version`)
* **chainId** — numeric chain identifier
* **verifyingContract** — zero address (signing happens off-chain)

### `primaryType`

Always `"TxSeismic"`.

## Example

```python
from seismic_web3 import build_seismic_typed_data
import json

typed_data = build_seismic_typed_data(unsigned_tx)
print(json.dumps(typed_data, indent=2))
```

## Notes

* The hash computed from this data matches [`eip712_signing_hash(tx)`](/clients/python/api-reference/eip712/eip712-signing-hash.md)
* The returned dict is JSON-serializable (no Python-specific types)

## Warnings

* If `tx.to` is `None`, it's encoded as the zero address
* All bytes fields must be `0x`-prefixed hex strings
* Ensure numeric values fit in their declared EIP-712 types (e.g. `uint64`)

## See Also

* [sign\_seismic\_tx\_eip712](/clients/python/api-reference/eip712/sign-seismic-tx-eip712.md) — signs using this data internally
* [eip712\_signing\_hash](/clients/python/api-reference/eip712/eip712-signing-hash.md) — computes hash from typed data
* [domain\_separator](/clients/python/api-reference/eip712/domain-separator.md) — domain component
* [struct\_hash](/clients/python/api-reference/eip712/struct-hash.md) — message component
* [UnsignedSeismicTx](/clients/python/api-reference/transaction-types/unsigned-seismic-tx.md) — input transaction type


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.seismic.systems/clients/python/api-reference/eip712/build-seismic-typed-data.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.