A landlord who wants to raise the rent to the local level must give reasons. Section 558a of the Civil Code says the request must be made to the tenant in text form and must be justified. The law names the usual kinds of evidence. Among them are the local rent index, the Mietspiegel, a rent database, a reasoned opinion by a publicly appointed and sworn expert, and the rents of comparable flats. For the last, naming three flats is enough. A landlord who ends a lease because of his own legitimate interest must also state the reasons in the letter. Other reasons count only if they arose later.