Caprola5 is a chemogenetic Ca[2+] recorder that is built from the self-labeling HaloTag chemical reporter. In the presence of both Ca[2+] and a fluorescent HaloTag ligand, Caprola5 undergoes irreversible chemical tagging by the HaloTag ligand, resulting in the recording of intracellular Ca[2+] increases during a defined period for later analysis. Sequential use of different HaloTag ligands (with different fluorescent properties) enables the recording of multiple periods of Ca[2+] changes in the same sample or organism. Caprola5 consists of Hpep1 (residues 145 to 154 of HaloTag), a GS linker, a Ca[2+]-binding protein (calmodulin), a Pro30 linker, a calmodulin-binding M13 peptide (RVDSSRRKFNKTAHALRAIGRLSSLE), a GGS linker and cpHaloΔ (circularly permuted HaloTag with residues 142-155 truncated) (PMID:38386755). For detailed kinetic and spectral properties, see PMID:38386755.