Abstract: Ultralight axions (ULAs) are a well-motivated class of hypothetical particles described by (pseudo)scalar fields, with extremely low masses ranging from about 10^{-33} to 10^{-18} eV. Depending on the mass, ULAs can be wave dark matter or serve as dynamical dark energy, featuring observational signatures distinct from ΛCDM. A defining characteristic of ULAs is rapid field oscillations at frequencies well above the Hubble rate especially at late times, making accurate and efficient cosmological predictions challenging. To address this, I present our algorithms, including effective fluid approximations and beyond, implemented in the publicly available code AxiECAMB, which covers numerical treatments of ULA evolution on linear scales across the full relevant mass range, enabling sub-percent accuracy predictions for current and next-generation cosmic microwave background and large-scale structure data analysis. I will discuss ULA effects on CMB and matter power spectra, highlight improvements to previous approaches, and explain how these advances refine constraints and may impact models suggested to resolve tensions around ΛCDM.