Blockchain gas fees. Use before sending a transaction on Base or Ethereum to choose fees and timing. Call GET with no parameters. Returns JSON per network: baseFeeGwei, priorityFeeGwei (p50, with p10/p90), suggestedMaxFeeGwei (2x base + priority), timingHint (cheap/normal/expensive vs the last 20 blocks) and simpleTransfer cost in ETH and USD, plus ethUsd. From eth_feeHistory with eth_gasPrice fallback. Descriptive, not a forecast. Errors are not charged. Paid per call via x402 (USDC on Base).