# Chains

`seismic-viem` provides pre-configured viem `Chain` objects with Seismic transaction formatters. These chain definitions include the correct chain IDs, RPC endpoints, and custom formatters needed for Seismic's type 0x4A transactions.

## Import

```typescript
import {
  seismicTestnet,
  sanvil,
  localSeismicDevnet,
  createSeismicDevnet,
} from "seismic-viem";
```

## Available Chains

| Chain           | Export               | Chain ID | RPC URL                                 | Description              |
| --------------- | -------------------- | -------- | --------------------------------------- | ------------------------ |
| Seismic Testnet | `seismicTestnet`     | 5124     | `https://testnet-1.seismictest.net/rpc` | Public testnet           |
| Sanvil          | `sanvil`             | 31337    | `http://127.0.0.1:8545`                 | Local Seismic Anvil      |
| Local Devnet    | `localSeismicDevnet` | 5124     | `http://127.0.0.1:8545`                 | Local seismic-reth --dev |

### Seismic Testnet

The public testnet for development and testing against a live Seismic network:

```typescript
import { http } from "viem";
import { privateKeyToAccount } from "viem/accounts";
import { createShieldedWalletClient, seismicTestnet } from "seismic-viem";

const client = await createShieldedWalletClient({
  chain: seismicTestnet,
  transport: http(),
  account: privateKeyToAccount("0x..."),
});
```

### Sanvil

Local development chain using Sanvil (Seismic's fork of Anvil). Chain ID `31337` matches Anvil/Hardhat defaults:

```typescript
import { http } from "viem";
import { privateKeyToAccount } from "viem/accounts";
import { createShieldedWalletClient, sanvil } from "seismic-viem";

const client = await createShieldedWalletClient({
  chain: sanvil,
  transport: http(),
  account: privateKeyToAccount("0x..."),
});
```

### Local Devnet

For running a local `seismic-reth --dev` node. Uses chain ID `5124` (same as testnet) but connects to `localhost`:

```typescript
import { http } from "viem";
import { privateKeyToAccount } from "viem/accounts";
import { createShieldedWalletClient, localSeismicDevnet } from "seismic-viem";

const client = await createShieldedWalletClient({
  chain: localSeismicDevnet,
  transport: http(),
  account: privateKeyToAccount("0x..."),
});
```

## Choosing a Chain

```
Are you developing against a live network?
  -> Use seismicTestnet

Are you running Sanvil locally for rapid iteration?
  -> Use sanvil

Are you running seismic-reth --dev locally?
  -> Use localSeismicDevnet

Do you need a custom chain configuration?
  -> Use createSeismicDevnet()
```

## SEISMIC\_TX\_TYPE

All chain configs use the Seismic transaction type constant:

```typescript
import { SEISMIC_TX_TYPE } from "seismic-viem";

console.log(SEISMIC_TX_TYPE); // 74 (0x4A)
```

The value `74` (`0x4A`) is the EIP-2718 transaction type envelope identifier for Seismic transactions. This constant is used internally by the chain formatters and encryption pipeline to identify and construct Seismic-specific transaction payloads.

## Chain Formatters

Each chain config includes `seismicChainFormatters` -- custom viem chain formatters that handle Seismic transaction fields. These formatters are applied automatically when you use a Seismic chain definition.

The formatters extend viem's standard transaction formatting to support the additional fields required by Seismic's type 0x4A transactions, including encryption metadata and signed read parameters.

{% hint style="info" %}
You do not need to configure or interact with `seismicChainFormatters` directly. They are embedded in every pre-configured chain object and in chains created via `createSeismicDevnet`.
{% endhint %}

## Custom Chain Factory

### createSeismicDevnet

Create a custom chain definition for any Seismic-compatible node:

```typescript
import { createSeismicDevnet } from "seismic-viem";

const myChain = createSeismicDevnet({
  nodeHost: "https://my-seismic-node.example.com",
  explorerUrl: "https://explorer.example.com",
});
```

#### Parameters

| Parameter     | Type     | Required | Description                                   |
| ------------- | -------- | -------- | --------------------------------------------- |
| `nodeHost`    | `string` | Yes      | Base URL of the Seismic node (without `/rpc`) |
| `explorerUrl` | `string` | No       | Block explorer URL for the chain              |

The factory returns a viem `Chain` object with:

* Chain ID `5124`
* RPC URL set to `{nodeHost}/rpc`
* Seismic chain formatters included
* Optional block explorer configuration

### Helper Factories

Convenience factories for common Seismic infrastructure:

```typescript
import { createSeismicAzTestnet, createSeismicGcpTestnet } from "seismic-viem";

// Azure-hosted testnet instance N
const azChain = createSeismicAzTestnet(1);

// GCP-hosted testnet instance N
const gcpChain = createSeismicGcpTestnet(1);
```

These generate chain configs pointing to numbered Seismic testnet instances on Azure and GCP infrastructure respectively.

## SeismicTransactionRequest

Seismic chain configs use a custom transaction request type that extends viem's standard `TransactionRequest` with Seismic-specific fields:

```typescript
interface SeismicTxExtras {
  encryptionPubkey: Hex; // Client's compressed secp256k1 public key
  encryptionNonce: Hex; // AES-GCM nonce for calldata encryption
  messageVersion: number; // Seismic message format version
  recentBlockHash: Hex; // Recent block hash for replay protection
  expiresAtBlock: bigint; // Block number at which the transaction expires
  signedRead: boolean; // Whether this is a signed read request
}
```

{% hint style="info" %}
You do not need to populate these fields manually. The shielded wallet client's encryption pipeline fills them automatically when sending transactions. They are documented here for reference and debugging purposes.
{% endhint %}

| Field              | Type      | Description                                               |
| ------------------ | --------- | --------------------------------------------------------- |
| `encryptionPubkey` | `Hex`     | Client's compressed secp256k1 public key                  |
| `encryptionNonce`  | `Hex`     | Random nonce for AES-GCM encryption of calldata           |
| `messageVersion`   | `number`  | Version of the Seismic message format                     |
| `recentBlockHash`  | `Hex`     | Recent block hash used for transaction replay protection  |
| `expiresAtBlock`   | `bigint`  | Block number after which the transaction becomes invalid  |
| `signedRead`       | `boolean` | `true` for signed read requests, `false` for standard txs |

## See Also

* [Installation](/clients/typescript/viem/installation.md) -- Install seismic-viem and viem
* [Seismic Viem Overview](/clients/typescript/viem.md) -- Full SDK overview and architecture
* Shielded Wallet Client -- Create a client using a chain config
* Encryption -- How calldata encryption uses chain-level formatters


---

# Agent Instructions: 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/typescript/viem/chains.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.