gas

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SKILL.md (first lines)

# Gas and Chain Cost

Your trained gas-price and ETH-price priors are stale. Never quote a transaction cost or exclude a chain for cost reasons without measuring the relevant chain now.

```bash
# Mainnet. If it fails: https://eth.drpc.org, https://rpc.flashbots.net
cast gas-price --rpc-url https://ethereum-rpc.publicnode.com

# Example L2; query the chain actually under consideration.
# Base fallback: https://base.publicnode.com
cast gas-price --rpc-url https://mainnet.base.org
```

`cast gas-price` returns the base fee plus a suggested tip — what a transaction actually pays, so it is the reading the formula below takes. `cast base-fee` returns the base fee alone; use it for setting `maxFeePerGas`, and never add a separate priority fee on top of a `gas-price` reading.

Do not replace a failed lookup with a remembered number. Fetch ETH/USD live before quoting dollars: the mainnet Chainlink feed at `0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419` (`latestRoundData`, 8 decimals), or `https://api.coinbase.com/v2/prices/ETH-USD/spot`.

Estimate the actual operation when possible. Otherwise state and justify the gas-used assumption:

```text
# Mainnet, and the execution half of any L2
cost_usd = gas_used × gas_price_gwei × 1e-9 × eth_usd

# On an OP-stack L2 the L1 data fee is a separate component and is not in
# gas_price. Read l1Fee off a recent receipt, or GasPriceOracle.getL1Fee at
# 0x420000000000000000000000000000000000000F — do not estimate it.
cost_usd = (gas_used × gas_price_gwei × 1e-9 + l1_fee_eth) × eth_usd
```

`cast gas-price` and `cast base-fee` print wei, not gwei — divide by 1e9. Check the converted figure back against the raw reading; a dropped or extra factor of 1e9 is the most common way a correctly measured chain still yields a stale-looking cost.

Choose from the measured workload:

- Keep mainnet viable for low-frequency, high-value actions unless another requirement favors an L2.
- Prefer an L2 for high-frequency, low-value, latency-sensitive, or L2-native activity.
- Do not choose an L2 merely because you remember mainnet gas being expensive.

Derive EIP-1559 fee fields from the target chain immediately before submission. Do not hardcode them or port a mainnet priority-fee constant to an L2.

For L2 optimization, measure which component dominates before deciding what to cut: compare `gasUsed × effectiveGasPrice` against `l1Fee` on current receipts. Do not import a pre-Dencun calldata-cost assumption, and do not assume the reverse either. Non-OP-stack rollups use different fee models, so measure them independently.

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From BuidlGuidl/ethskills-evals, MIT.

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