The UV absorption diagnostic demonstrates unparalleled sensitivity, in-situ capability, non-intrusiveness, with impressive time resolution. With a ppm-level detection limit, even using a single-pass configuration at combustion-relevant temperatures, it enables high-fidelity kinetic experiments with highly diluted gas mixtures under nearly constant-temperature conditions. Our sensitive UV diagnostics for radicals (such as allyl radical and OH radical) and molecules (including 1,3-butadiene and isoprene) facilitate comprehensive investigations of key species’ time evolution, rate coefficients, branching ratios, and rate rules. These measurements improve our understanding of combustion properties of both conventional and bio-derived fuels, benefiting automatic modeling studies.