Experiments at $e^{+}e^{-}$ colliders, such as BaBar, Belle and Belle~II, provide an excellent environment for precision studies of $\tau$-lepton decays. BaBar and Belle have completed their data taking with final integrated luminosities of $0.5~\mathrm{ab^{-1}}$ and $1.0~\mathrm{ab^{-1}}$, respectively. The integrated luminosity collected by Belle~II up to 2025 amounts to about $0.6~\mathrm{ab^{-1}}$, and data taking is ongoing toward a final goal of $50~\mathrm{ab^{-1}}$. Their clean collision conditions and large datasets enable stringent tests of lepton flavor universality (LFU) and highly sensitive searches for lepton flavor violation (LFV). We present recent results from Belle and Belle~II on LFU tests in $\tau \rightarrow \ell \nu \bar{\nu}$ decays and LFV searches such as $\tau \rightarrow \mu\mu\mu$, $\tau \rightarrow e^{\pm}\ell^{\mp}\ell'^{-}$, and $\tau \rightarrow \ell K_S^0$, as well as prospects for future improvements.