Studies and research concerning digital games and utilising them in mathematics education concentrates heavily on the learning effects of games. Yet, little attention is paid in analysing the games before they are applied for research - the games are often simply described on general level. Therefore, a qualitative content analysis tool was created by combining theories of game's two- layered structure and theories of educational digital game design in order to reveal the relationship of learning content and game structure. This article is reviewing the possibilities, pros and cons of the analysis tool created for the author's education master's thesis in 2013. The data for a study which used this analysis tool was collected by the researcher (author) as an analytical player from 48 different mathematical educational digital games of former Opit- service for a research for master's thesis in 2013. The relationship was described using qualitative content analysis tool created for the task. First, the framework separated the two- layer model of game -- the core (rules, mechanics, conflict and goals) and the shell (representation) after which the learning content's relationship to these different parts was revealed by using the analysis tool. As the game's core and shell were described in to their parts (rules, mechanics etc.) the analysis tool directed the questions to the different parts separately. The analysis tool's questions about the core were aimed to solve the learning content's relationship to the core, whether the learning content is in intrinsic relationship or if the relationship is extrinsic. The analysis of the shell aimed to see has the learning content anything to do with the actual representation. The results of using this analysis tool found out that in the most of the games, mathematical learning content were considered to be in intrinsic relationship with the core of a game. However, only minority of the games used the visual representation to link the learning content to a concrete context. The analysis tool is yet used only in one study by author. Analysis with the actual tool is straight forward and relies heavily on the description of the game's core and shell. However, this enables the researcher to " interview" or " observe" the targeted games or also analyse game descriptions made by third party (whether it is a colleague or a student). The tool has also a possibility to aid the educational game designers in order to affect the learning outcomes of their games. Even though the mathematical educational games were digital, the analysis tool itself is not limited to digital- only games and can also be used without modification for tabletop games and different subject than mathematics. Although the analysis tool is in need for further testing and development, it provides an organised and straight forward option to the field of educational game research.