Measuring Gas
Profiling tools.
Measure, Don't Guess
Gas optimization without measurement is guesswork. The compiler, opcode costs, and access patterns interact in non-obvious ways, so an intuitive change can sometimes make things worse.
Always profile before and after. A change that does not reduce measured gas is not an optimization, no matter how clever it looks.
Forge Gas Reports
Foundry's forge test --gas-report prints a per-function table of min, average, median, and max gas usage across all your tests. It is the fastest way to spot expensive functions.
$ forge test --gas-report
| Function | min | avg | median | max | # calls |
| transfer | 28012 | 34521 | 34521 | 51012 | 12 |
| approve | 24300 | 24300 | 24300 | 24300 | 5 |