# Customize Gas

Fordefi simplifies the process of creating EVM transactions by automatically estimating the gas limit and setting the gas price based on current market gas prices. However, users who seek more control can customize the gas price and gas limit of their transactions.

## Customize gas price

When creating an EVM transaction, you can specify the gas price, by populating the `details.gas` field of the [Create Transaction](/api/openapi/transactions/create_transaction_api_v1_transactions_post) request.

There are two ways to specify it:

- The simplest way is to let Fordefi set the gas price based on the chain's current gas price. You can choose between `low`, `medium`, and `high` gas levels, which translate to different percentiles of recent gas prices. To do this, set the `type` to `priority` and the `priority_level` to one of the following: `low`, `medium`, or `high`.
- You can also specify a gas price in wei manually. To do this, set the `type` to `custom`. On chains that have adopted EIP-1559, then set `max_priority_fee_per_gas` and `max_fee_per_gas`. On chains that use legacy gas pricing, set the `gas_price`.


If you omit the `details.gas` field altogether, Fordefi will use the `medium` priority by default.

Examples:

Priority Gas

```json
{
    "vault_id": "16b5aa12-509e-4944-b656-cf096515d627",
    "signer_type": "api_signer",
    "type": "evm_transaction",
    "details": {
        "type": "evm_raw_transaction",
        "chain": "ethereum_mainnet",
        "to": "0x565697B5DD1F7Bdc61f774807057D058E5A27cbC",
        "value": "0",
        "data": {
            "type": "hex",
            "hex_data": "0x0d1d7ae50000000000000000000000000000000000000000000000000000000000000006"
        },
        "gas": {  // [!code warning:4]
            "type": "priority",
            "priority_level": "high" 
        }
    }
}
```

Custom Gas – EIP1559

```json
{
    "vault_id": "16b5aa12-509e-4944-b656-cf096515d627",
    "signer_type": "api_signer",
    "type": "evm_transaction",
    "details": {
        "type": "evm_raw_transaction",
        "chain": "ethereum_mainnet",
        "to": "0x565697B5DD1F7Bdc61f774807057D058E5A27cbC",
        "value": "0",
        "data": {
            "type": "hex",
            "hex_data": "0x0d1d7ae50000000000000000000000000000000000000000000000000000000000000006"
        },
        "gas": {  // [!code warning:8]
            "type": "custom",
            "details": {
                "type": "dynamic",
                "max_priority_fee_per_gas": "1000000000", // 1 Gwei
                "max_fee_per_gas": "20000000000" // 20 Gwei
            }
        }
    }
}
```

Custom Gas – Legacy

```json
{
    "vault_id": "16b5aa12-509e-4944-b656-cf096515d627",
    "signer_type": "api_signer",
    "type": "evm_transaction",
    "details": {
        "type": "evm_raw_transaction",
        "chain": "ethereum_mainnet",
        "to": "0x565697B5DD1F7Bdc61f774807057D058E5A27cbC",
        "value": "0",
        "data": {
            "type": "hex",
            "hex_data": "0x0d1d7ae50000000000000000000000000000000000000000000000000000000000000006"
        },
        "gas": {  // [!code warning:7]
            "type": "custom",
            "details": {
                "type": "legacy",
                "gas_price": "20000000000" // 20 Gwei
            }
        }
    }
}
```

## Customize gas limit

The gas limit is the maximum amount of gas that can be used to execute the transaction. By default, it is set automatically by Fordefi using the `eth_estimateGas` method of the node's JSON-RPC interface.

You can optionally specify a custom gas limit by setting the `details.gas.gas_limit` field in the [Create Transaction](/api/openapi/transactions/create_transaction_api_v1_transactions_post) request. If omitted, Fordefi will automatically estimate an appropriate gas limit for the transaction.

Example with custom gas limit:


```json
{
    "vault_id": "16b5aa12-509e-4944-b656-cf096515d627",
    "signer_type": "api_signer",
    "type": "evm_transaction",
    "details": {
        "type": "evm_raw_transaction",
        "chain": "ethereum_mainnet",
        "to": "0x565697B5DD1F7Bdc61f774807057D058E5A27cbC",
        "value": "0",
        "data": {
            "type": "hex",
            "hex_data": "0x0d1d7ae50000000000000000000000000000000000000000000000000000000000000006"
        },
        "gas": {
            "type": "priority",
            "priority_level": "medium",
            "gas_limit": "1000000" // // [!code warning]
        }
    }
}
```