<p>Studies worldwide document that climate adaptation is still insufficiently implemented in urban planning practice. Practice Guidelines are regarded as an important tool for municipal adaptation by providing measures for development planning. However, little is known about how this mainstreaming is accepted and implemented in practice. To address this, 24 heat adaptation measures were evaluated by two municipal planners over 7 h of semi-structured interviews. The case study was embedded in a research project accompanying an actual local land-use process in Germany. According to their assessment, the literature contained measures that are: (i) regularly used in the development plan (3 of 24), (ii) could be used reluctantly (5 of 24), (iii) only indirectly applicable or serve as overall objectives (6 of 24), (iv) unfamiliar or not trusted (2 of 24) and (v) not applicable in the context of development planning (8 of 24). This study provides firsthand insight into a planning department’s perspective on integrating climate adaptation into development plans. The findings reveal fundamental shortcomings in the decision-making flexibility of planners and their support by ministries and politicians, but also highlight the planners’ autonomy to ignore adaptation measures. Systemic and legal barriers currently prevent comprehensive municipal climate adaptation.</p>