Devices, systems and methods for digital video process are described. An exemplary method for video processing includes performing a conversion between a current video block of a video and a coded representation of the video, wherein the performing of the conversion includes determining, based on a width (W) and/or a height (H) of the current video block, an applicability of a secondary transform tool to the current video block, and wherein the secondary transform tool includes applying, during encoding, a forward secondary transform to an output of a forward primary transform applied to a residual of a video block prior to quantization, or applying, during decoding, an inverse secondary transform to an output of dequantization of the video block before applying an inverse primary transform.