Developers spend a significant amount of time trying to understand code bases. To aid developers' comprehension of code, researchers have developed software visualization tools. However, the uses of these tools in situ have rarely been investigated. To make matters worse, as studies have revealed, developers seldom use diagramming tools, making such investigations a challenge. To determine the possible uses of such tools in real practice, we conduct a diary study in which eleven developers in real-world developments use a novel visualization tool (a graphical code recommender) for one month. In the study, we ask what information and features the visualization and diagramming tools should provide to aid developers' work according to their situations. The study reveals the situations in which developers would use such visualization and diagramming tools and also the concrete requirements for such tools that would make them useful. (C) 2016 Elsevier Inc. All rights reserved