Software engineering (SE) requires high analytical skills and creativity, which makes it an excellent context for experiencing flow. Although previous work in the SE context has identified how positive affect and development tools can support the flow experience, there is still much to uncover about the characteristics of software developers’ flow experiences. To address this gap in knowledge, we conducted a qualitative critical incident technique (CIT) questionnaire (n = 401) on the flow-facilitating factors and characteristics of flow in the SE context. The most important flow-facilitating factors in developers’ work included optimal challenge, high motivation, positive developer experience (DX), and no distractions or interruptions. The flow experiences were characterized by absorption, effortless control, intrinsic reward, and high performance. Our study identifies the features of flow commonly addressed in flow research; however, it also highlights how IT use, especially development tools that provide positive DX, as well as being able to work without excessive distractions and interruptions are important facilitators of developers’ flow.