Mathematical problem-solving keys work as a visual tool for getting familiar with heuristics for a variety of mathematical problems in Primary Schools. Keys are modified from problem-solving approaches outlined in Singaporean Mathematics Curriculum 2013 and visual tools by Herold-Blasius and Rott (2016) and Herold-Blasius (2021). Keys can be printed out, cut and laminated to create a personal set of keys for each student. Keys work as a visual reminder on a variety of techniques to solve different problems. They can be introduced as tools to "unlock" for example word problems or open-ended problems with multiple solution strategies. It is recommended that the teacher first guides students on what each key practically means: where to start and how to assess whether the approach or end-result makes sense.