The study presents phase-resolved emission spectra of the hot Jupiter WASP-43b, measured with the JWST's MIRI instrument from 5 to 12 µm. The spectra reveal a large day-night temperature contrast (1524 ± 35 K and 863 ± 23 K) and evidence for water absorption at all orbital phases. Comparisons with three-dimensional atmospheric models suggest the presence of optically thick nightside clouds. The dayside is consistent with a cloudless atmosphere. Methane is not detected on the nightside (2σ upper limit of 1–6 ppm), contradicting equilibrium chemistry models but consistent with disequilibrium kinetics. The results indicate that the atmosphere of WASP-43b is shaped by disequilibrium processes, with nightside clouds affecting thermal emission. However, discrepancies between observations and models highlight the need for further exploration of cloud and disequilibrium chemistry effects in numerical models. The study also finds that the observed phase curve and emission spectra provide new constraints on the optical thickness and pressure of nightside clouds. Atmospheric retrieval models show water vapour abundance consistent with solar composition, while methane upper limits are more consistent with disequilibrium models. The presence of nightside clouds is supported by the muted emission spectra and the need for isothermal temperature profiles. The study highlights the capabilities of JWST/MIRI for exoplanet atmosphere characterization and the importance of further exploring cloud and disequilibrium chemistry in models.The study presents phase-resolved emission spectra of the hot Jupiter WASP-43b, measured with the JWST's MIRI instrument from 5 to 12 µm. The spectra reveal a large day-night temperature contrast (1524 ± 35 K and 863 ± 23 K) and evidence for water absorption at all orbital phases. Comparisons with three-dimensional atmospheric models suggest the presence of optically thick nightside clouds. The dayside is consistent with a cloudless atmosphere. Methane is not detected on the nightside (2σ upper limit of 1–6 ppm), contradicting equilibrium chemistry models but consistent with disequilibrium kinetics. The results indicate that the atmosphere of WASP-43b is shaped by disequilibrium processes, with nightside clouds affecting thermal emission. However, discrepancies between observations and models highlight the need for further exploration of cloud and disequilibrium chemistry effects in numerical models. The study also finds that the observed phase curve and emission spectra provide new constraints on the optical thickness and pressure of nightside clouds. Atmospheric retrieval models show water vapour abundance consistent with solar composition, while methane upper limits are more consistent with disequilibrium models. The presence of nightside clouds is supported by the muted emission spectra and the need for isothermal temperature profiles. The study highlights the capabilities of JWST/MIRI for exoplanet atmosphere characterization and the importance of further exploring cloud and disequilibrium chemistry in models.