## 1 Introduction  
Requirements engineering in Agile software development deals with various challenges, including poorly specified requirements, which result in inaccurate scope estimation [1]. This is especially prevalent in early phase project scope estimation, which must be performed before the software development project starts. During this early phase, initial requirements must be obtained from the client. Based on them, the scope of the product must be estimated and agreed upon to proceed further with the project execution. Estimation must be performed from a limited amount of data, since stakeholders are willing to allocate a limited amount of time and personnel to preliminary elicitation of the product requirements. However, the scope estimation must be as precise as possible, because it is used to develop a contract with the client and serves as a basis for more detailed requirement elicitation if stakeholders commit to the project. In Agile software development projects, capturing domain knowledge can be challenging [2]. During requirement elicitation, stakeholder communication plays a crucial role. Although in Agile projects, requirements are commonly specified using User stories and Story maps, additional visualizations can be helpful in facilitating discussions, in understanding and communicating the requirements to the client and within the development team [2, 3, 4]. These visualizations in the form of various diagrams can significantly enrich the definition of the system under development and enhance the understanding of the project scope. If we choose not only to document user stories that reflect individual requirements, but to model domain knowledge including its behavioral aspects, we acquire a broader view of future product behavior and structure [2]. UML [5] diagrams are one of the popular choices for modeling software requirements. SysML [6] is also a popular notation for systems of systems modeling. Although Agile software development methodologies do not explicitly suggest the use of models to specify requirements, there are various approaches that discuss the benefits of introducing modeling into Agile development [4; 7; 8]. When introducing the usage of models in Agile requirement elicitation, it must be considered that these models can be prepared as sketches. They cover the details from different points of view, as they are prepared by different members of the team. Requirements can be overlapping, not aligned in the terms of the domain vocabulary, and even contradicting. Therefore, the alignment and reconciliation of these models must also be considered, ensuring that the information depicted in the models is useful in the project and can also serve as a basis for project scope estimation. Support for diverse sources of requirements and identifying overlapping requirements is crucial for resource and stakeholder management [9], risk identification and mitigation [10; 11], and ensuring that the final product meets its intended objectives. It contributes to better stakeholder involvement and higher-quality results, thus improving stakeholder satisfaction [12; 13]. The goal of this paper is to facilitate an early-phase Agile software development project scope estimation based on the elicitation and reconciliation of requirements presented in various forms. The objectives are to propose a methodology for early phase scope estimation, to develop a tool for facilitating the application of the methodology, and to apply it in a case study of a real-life software development project. We aim to demonstrate that the proposed methodology enables gathering a more detailed and reconciled requirements list, which then can be used for scope estimation in the early phase of Agile project.