We present the first precise calculations of the gravitational quasinormal-mode (QNM) frequencies for spinning black holes with dimensionless angular momenta $J/M^2≔a\lesssim 0.75$ in dynamical Chern-Simons gravity. Using the metric perturbations with spectral methods (METRICS) framework, we compute the QNM frequencies of both axial and polar metric perturbations, focusing on the $nlm=022$, 033, and 032 modes. The METRICS frequencies for the 022 mode achieve numerical uncertainties $\lesssim {10}^{-4}$ when $0\le a\le 0.5$ and $\lesssim {10}^{-3}$ for $0.5\le a\le 0.75$, without decoupling or simplifying the linearized field equations. We also derive optimal fitting polynomials to enable efficient and accurate evaluations of the leading-order frequency shifts in these modes. The METRICS frequencies and fitting expressions are a robust and indispensable step toward enabling gravitational-wave ringdown tests of dynamical Chern-Simons gravity.

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• Classical black holes
• Gravitational waves
• Astronomical black holes