Had a similar experience with my Rust implementation for JSONLogic expression evaluation engine. As it has a full test suite with 1000s of cases and a benchmarking script, I was able to give some basic hints to try different optimization techniques and the end result was impressive. Reached from 1.6s to 200ms for a full benchmarking test. https://github.com/GoPlasmatic/datalogic-rs First 3 versions were hand written and maintained for 3yrs, and now 4th version came out in less than a month's time with impressive performance.