Catalyzes the hydrolysis of acyl-CoAs into free fatty acids and coenzyme A (CoASH), regulating their respective intracellular levels (PubMed:16951743). Preferentially hydrolyzes acetyl-CoA (PubMed:16951743). . This is the function of ACOT12 (acyl-CoA thioesterase 12, ENSG00000172497).