Analysis of the clarity with which Spanish academic journals report their preprint acceptance policies in the instructions to authors. The aim is to determine to what extent these journals have adopted explicit policies on preprints and how these policies align with the transparency recommendations of the Committee on Publication Ethics (COPE). An analysis was made of the preprint acceptance policies of 221 Spanish academic journals classified in Q1 and Q2 quartiles of the Scimago Journal & Country Rank (SJ&CR) 2022. The instructions to authors and self-archiving policies on the journals' websites were examined, as well as the Open Policy Finder (OPF) and Dulcinea directories. The journals were classified into four categories: explicit acceptance, explicit rejection, unclear mention and no mention. Only 17.6% of the journals analysed clearly state their policy on preprints. 15.4% explicitly accept preprints, while 2.3% explicitly reject them. 40.3% make confusing statements and 42.1% make no mention of preprints. The study reveals that the majority of Spanish academic journals do not comply with the COPE recommendation for clarity regarding preprints, meaning there is significant room for improvement in the way journals present their policies on preprints. Health and experimental science journals are clearer and more inclined to accept preprints. In addition, inconsistencies are observed between the self-archiving policies declared in the self-archiving policy directories and the instructions on the journals' websites.